Citologia della Cellula Epatica nel Corso della Iperglicemia Sperimentale

Riassunto L'A. ha studiato le successive modificazioni citologiche delle cellule epatiche in seguito alla introduzione in circolo di glucosio in dosi varie, ma sempre elevate. Con il metodo di Hagedorn-Jensen sono state determinate le curve glicemiche durante tutto il periodo degli esperimenti (48–60 ore). Come animale da esperimento è stato usato il coniglio e gli esperimenti sono stati condotti in 4 modi diversi: 1° Iniezione di 20 gr. di glucosio in una sola volta. 2° Iniezione endovena di 15 gr. di glucosio frazionatamente in 3 volte. 3° Iniezioni giornaliere di 5–10 gr. di glucosio; gli esperimenti sono durati 72–80 ore. 4° Perfusione del fegato con una soluzione di glucosio a concentrazione variabile dal 2% al 4%; la perfusione veniva fatta attraverso una vena mesenterica che veniva poi legata.Prima di iniettare la soluzione di glucosio si apriva l'addome dell'animale con tutte le precauzioni della asepsi e si prelevava un pezzetto di fegato che veniva utilizzato come controllo dell'esperimento; a intervalli di tempo stabiliti si prelevavano altri pezzetti di fegato riaprendo la ferita addominale; contemporaneamente da una vena periferica si prelevava la quantità di sangue necessaria per la determinazione della glicemia.Il citoplasma anisto delle cellule epatiche presenta le seguenti caratteristiche: nel controllo (48 h. di digiuno) il citoplasma è colorabile diffusamente in modo abbastanza intenso; dopo 3 h. dalla iniezione si nota la comparsa di grandi spazi chiari che occupano la maggior parte del eitoplasma; dopo 6–8 h. dalla iniezione il citoplasma comincia a ridivenire più colorabile ed omogeneo; permangono zone non occupate da condriosomi, ma da una sostanza che con la ematossilina di Heidenhain si tinge in un grigio leggermente diverso da quello del citoplasma anisto circostante. La comparsa dei grandi spazi chiari corrisponde ai valori massimi della curva glicemica; quando il tasso di glucosio tende ad awicinarsi a valori normali il citoplasma si presenta sempre nettamente omogeneo.Il contenuto in glicogene sale gradatamente e raggiunge il suo massimo 18–24 ore dopo la iniezione; da questo momento fino al termine degli esperimenti non subisce variazioni o subisce solo una lieve dimunizione. L'A. non condivide la ipotesi espressa da altri ricercatori che gli spazi chiari siano pieni di glicogene; pensa piuttosto che in questi spazi si trovi del glucosio che sarebbe cosi in un primo tempo come accantonato nella cellula; in un secondo tempo questo materiale diffonderebbe nel citoplasma anisto circostante per subire il processo di polimerizzazione.Il condrioma ha forma di bastoncini molto lunghi e sottili nei preparati di controllo; quando nel citoplasma anisto compaiono le grandi aree chiare i condriosomi si addensano nelle travate di citoplasma non modificato. In alcuni casi si nota un lieve accorciamento dei condrioconti e la comparsa di qualche granulo. L'A. ritiene la prima modificazion dovuta ad un fattore meccanico, la seconda dovuta alle variazioni fisico-chimiche che si verificano nella cellula epatica durante la deposizione di glicogene.Quando la glicemia oscilla su valori di 1,40–2 si nota una dilatazione assai forte di tutti i capillari biliari e l'orletto di citoplasma che circonda i capillari biliari è assolutamente libero di condrioma.I valori delle superfici cellulari salgono gradatamente e dopo 18 h. raggiungono il loro massimo; quasi subito si inizia una graduale discesa e dopo 24 h. i valori delle superfici cellulari sono simili a quelli del controllo. Il volume dei nuclei subisce variazioni regolarissime. Alla iniezione di glucosio segue una graduale ascesa, che alla 16^a–17^a ora raggiunge il suo vertice, per poi diminuire gradatamente e tornare alla norma dopo 40–48 ore. Dal confronto fra la curva dei valori nucleari e contenuto in glicogene della cellula epatica nei vari periodi degli esperimenti, l'A. rileva che le variazioni dei volumi nucleari sono in rapporto più che con il contenuto in glicogene della cellula epatica, con la attività glicogenetica della cellula stessa.È stato osservato un considerevole aumento del numero delle cellule binucleate, che al termine degli esperimenti sono assai più numerose che nei preparati di controllo.

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Zusammenfassung Der Verfasser hat die aufeinanderfolgenden zytologischen Veränderungen der Leberläppchenzellen nach Einführung von verschiedenen, aber immer erhöhten Glukosedosen in den Blutkreislauf verfolgt.Mit der Methode von Hagedorn und Jensen wurden die glykämischen Kurven während der ganzen Dauer der Versuche (36–48 Stunden) bestimmt. Als Versuchstier wurde das Kaninchen benutzt, und die Versuche wurden auf 4 verschiedene Arten durchgeführt: 1. Endovenöse Injektion von 20 g Glukose auf einmal. 2. Endovenöse Injektion von 15 g Glukose verteilt auf dreimal. 3. Tägliche Einspritzungen von 5 bis 10 g Glukose; die Versuchsdauer betrug 72–80 Stunden. 4. Einschwemmung der Leber mit einer 2–4%igen Glukoselösung; die Einschwemmung wurde durch eine Vena mesenterica gemacht, die dann abgebunden wurde.Vor Einspritzung der Glukoselösung wurde das Abdomen des Tieres unter strenger Asepsis geöffnet und ein Stück Leber entnommen, das zur Versuchskontrolle diente: in bestimmten Zeitabschnitten wurden andere Leberstücke entnommen, indem ich die Abdominalwunde wieder öffnete; zugleich wurde aus einer peripheren Vene die für die Glukosebestimmung notwendige Blutmenge entnommen.Das Zytoplasma der Leberzellen weist folgende Merkmale bei der Kontrolle (48 Stunden Fasten) auf: Das Zytoplasma ist homogen und ist ziemlich stark gleichmäßig färbbar; 3 Stunden nach der Einspritzung erscheinen große, helle Räume, die den größten Teil des Zytoplasmas einnehmen; 6–8 Stunden nach der Einspritzung beginnt das Zytoplasma wieder färbbarer und homogener zu werden: es bleiben Zonen, die nicht von Chondriosomen eingenommen sind, sondern von einer Substanz, die sich mit Heidenhainschem Hämatoxylin in einem Grau färbt, das etwas verschieden von dem des untenstehenden strukturlosen Zytoplasmas ist. Das Erscheinen der großen hellen Räume entspricht den Höchstwerten der glykämischen Kurve, die allmähliche Rückkehr zur Gleichförmigkeit fällt mit dem allmählichen Absinken der glykämischen Kurve zusammen: wenn der Glukosegehalt sich den Normalwerten nähert, stellt sich das Zytoplasma immer ganz homogen dar. Das Chondriom hat in den Kontrollpräparaten die Form sehr langer und dünner Stäbchen: wenn im strukturlosen Zytoplasma die großen hellen Räume erscheinen, verdichten sich die Chondriosomen in den nicht veränderten Zytoplasmabalken: in einigen Fällen bemerkt man eine leichte Verkürzung des Chondrioconten und das Erscheinen von einigen Körnchen; der Verfasser hält die ersterwähnten Veränderungen für durch einen mechanischen Faktor verursacht, die zweiten durch physikalisch-chemische Variationen, die sich in der Leberzelle während der Glykogenablagerung einstellen.Wenn die Glykämie sich in Werten zwischen 1,40–2 bewegt, bemerkt man eine sehr starke Erweiterung aller Gallenkapillaren, und daß der Zytoplasmarand, welcher die Gallenkapillaren umgibt, ganz ohne Chondriom ist.Die Werte der Zelloberflächen weisen sehr deutliche Veränderungen auf; nach der Einspritzung steigen die Werte allmählich und erreichen nach 18 Stunden ihren Höchststand; fast augenblicklich beginnt ein schrittweises Sinken der Zelloberflächen, und nach 24 Stunden sind die Werte ähnlich denen der Kontrolle. Auch die Werte der Kernvolumina verhalten sich sehr regelmäßig: nach der Einspritzung steigen sie schnell und allmählich erreichen sie nach 18 Stunden ihren Höchststand; von diesem Moment ab beginnt eine allmähliche Verminderung; 40 bis 48 Stunden nach der Einspritzung sind die Werte ungefähr normal. Aus dem Vergleich der Kurve der Kernvolumina mit dem Glykogengehalt der Leberzellen in verschiedenen Perioden der Versuche ergibt sich, daß die Veränderungen der Kernvolumina mehr mit der glykogenetischen Tätigkeit der Leberzelle als mit dem Glykogengehalt derselben in Beziehung stehen.Es ist eine beachtliche Zunahme der Zweikernzellen zu bemerken.

     

Adelchi Negri and Schools of General Pathology in Italy between the end of the nineteenth and beginning of the twentieth century

The long lasting scientific collaboration of Adelchi Negri with Camillo Golgi in the Laboratory of General Pathology and Histology of Pavia began in 1898–99, when he was still a medical student, and at about the time basic knowledge about human malaria transmission cycle (to which Golgi himself had given important contributions) was completed. On the occasion of the 100^th anniversary of the discovery of Negri bodies, this article provides a short overview of the scientific and cultural context in whichNeurocytes hydrophobiae hypothesis matured. To the same intent and purposes, this article also delineates some of the important scientific achievements in the field of General Pathology by Negri’s contemporaries, reflecting both the influence of the two great pioneers in the field (Bizzozero and Golgi), and the close contact with European science in the 1890’s to the end of the first World War, when biological science in Italy entered a new crisis.

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Adelchi Negri e le Scuole di Patologia generale nel passaggio dall’Ottocento al Novecento

Riassunto  La lunga collaborazione scientifica di Adelchi Negri con Camillo Golgi, nel Laboratorio di Patologia generale ed Istologia di Pavia, ebbe inizio nel 1898–99, quando questi era ancora studente di Medicina, e la conoscenza di base sul ciclo di trasmissione della malaria nell’uomo (alla quale lo stesso Golgi aveva dato importanti contributi in studi pionieristici) era completata. In occasione del Centenario della scoperta dei Corpi del Negri, questo articolo offre una rassegna sintetica del contesto scientifico-culturale in cui maturò l’ipotesi delNeurocytes hydrophobiae come agente causale della rabbia. Con questo intento e per lo stesso scopo, questo articolo traccia anche alcuni degli importanti raggiungimenti scientifici nel campo della Patologia generale da parte dei contemporanei di Negri, nei quali è rinvenibile, sia l’influenza dei grandi pionieri della disciplina (Bizzozero e Golgi), sia lo stretto contatto con la scienza europea, tra il 1890 circa e la fine della prima guerra mondiale, allorché la scienza biologica italiana entrò in una nuova crisi.

     

I fenomeni neurosecretori nella femmina del tritone crestato in condizioni sperimentali

Riassunto L'A. ha studiato il sistema ipotalamo-ipofisario della femmina del Tritone crestato normale e nelle seguenti condizioni sperimentali: lesioni ipotalamiche, ipofisectomia, carico osmotico, allevamento in ambiente secco, trattamento con acetato di rame. Negli animali ipotalamo-lesi in estate o allevati a temperatura artificiale di tipo estivo in inverno, l'A. ha osservato in un primo tempo un aumento dell'attività secretoria nelle cellule del n. m. p., che poi declina per esaurirsi completamente 50 giorni circa dopo Fintervento operatorio, senza che ne segua atrofia cellulare. Il neurosecreto si accumula nel moncone prossimale del f. preottico-ipofisario, le cui fibre lentamente degenerano in direzione pètale. Nella neuroipofisi l'atrofia tissulare e la rarefazione di sostanza neurosecretoria, già apprezzabile dopo 9 giorni, appaiono estremamente spinte dopo 50 giorni circa. L'atrofia della neuroipofisi, la deplezione in essa del neurosecreto, e il calo dell'attività secretoria nelle cellule del n. m. p. sono meno accentuate negli animali allevati, d'inverno, a temperatura naturale.Negli animali ipofisectomizzati l'A. ha osservato che durante la prima settimana l'attività secretoria nelle cellule del n. m. p. tende ad aumentare. Dal 12° giorno in poi lentamente declina, ma non si esaurisce del tutto neppure dopo 36 giorni, ed entro questo termine le cellule secernenti non degenerano. La quantità di neurosecreto entro le fibre del f. preottico-ipofisario è scarsa nei primi tre giorni, aumenta e si mantiene rilevante dal 5° al 12° giorno, e progressivamente poi diminuisce, senza mai scomparire del tutto. In corrispondenza del tuber le fibre del f. preottico-ipofisario degenerano, e in esse si accumula sostanza neurosecretoria. La degenerazione progredisce lentamente in direzione petale.Il carico osmotico (allevamento in soluzione all'1% di cloruro di sodio) tanto in animali integri che in animali ipotalamo-lesi ha portato, nel corso di 10 giorni, alla degenerazione delle cellule neurosecernenti del n. m. p., ad una forte diminuzione del neurosecreto entro gli assoni del f. preottico-ipofisario e ad una netta deplezione della colloide neuroipofisaria, non accompagnata da mitosi nei piuiciti.Del pari l'allevamento in ambiente secco ha determinato solo in un primo tempo un'esaltazione dei fenomeni neurosecretori nelle cellule del n. m. p. e un incremento dei fenomeni di trasporto lungo la via neurosecretoria; in un secondo tempo però subentrano fatti degenerativi a carico delle cellule secernenti e una più o meno marcata deplezione della colloide nella neuroipofisi.Infine gli effetti ottenuti con iniezioni di acetato di rame sono troppo poco netti per autorizzare qualsiasi deduzione.     

Ricerche ultrastrutturali sulla distribuzione del glicogeno nelle cellule dell'embrione di pollo in rapporto alla presenza delle inclusioni vitelline

Riassunto L'autore ha condotto uno studio al microscopio elettronico sulla distribuzione e sulla genesi del glicogeno nelle cellule dell'embrione di pollo nei primi stadi dello sviluppo.L'autore riscontra che nelle prime ore di incubazione il glicogeno è presente in pressochè tutte le cellule del blastoderma, dove coesiste con inclusioni vitelline. Al 2° giorno di incubazione il glicogeno scompare in tutte le cellule che hanno interamente digerito le inclusioni vitelline, rimanendo invece solo in quelle che sono ancora rieche di vitello. Fanno eccezione le cellule del miotoma che, pur essendo sprovviste di vitello, nella terza giornata di incubazione accumulano glicogeno in notevole quantità, in coincidenza con la comparsa in esse délie miofibrille.L'autore ritiene ehe il glicogeno che si trova inizialmente nelle cellule embrionali si formi in gran parte per attività neoglicogenetica, a partire dal vitello contenuto nelle cellule medesime, Egli conclude che tale attività neoglicogenetica dapprima sia propria di tutte le cellule embrionali, fino a quando hanno inclusioni vitelline, e che poi essa rimane localizzata al solo epitelio del sacco vitellino che sempre contiene vitello.

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Ultrastructural investigations on the distribution of glycogen in the cells of chick embryo in relation to the presence of yolk inclusions

Summary The distribution and genesis of glycogen in the embryonic cells of chickens in the first stages of development has been investigated electronmicroscopically.In the first hours of incubation the glycogen is present in almost all the cells of the blastoderm where it coexists with yolk inclusions. On the second day of incubation the glycogen disappears in all the cells that have completely digested the yolk inclusions and remains only in those that are still rich in yolk. The only exceptions are the myotome cells that, being that they do not have yolk in the third day of incubation, accumulate glycogen in notable quantities coincidental to the appearance of myofibrils.The author holds that the glycogen that is found initially in the embryonic cells has its origin, for the most part, from neoglycogenetic activity, starting from the yolk contained in the cells themselves. It is concluded that this neoglycogenetic activity initially is present in all the embryonic cells, while they still have inclusions, and then remains localized only in the epithelium of the yolk sac that always contains yolk.

     

Le allergopatie respiratorie in abitanti nell'isola di Capri: Correlazione con i fattori meteorologici

Riassunto Sia le piante spontanee, in particolare la Parietaria e le Graminacee, sia le piante coltivate, i cui pollini hanno in vario grado importanza allergologica, sono abbondantemente rappresentate e diffuse sull'isola di Capri. Gli estratti di acari Dermatophagoides, però, risultano di gran lunga gli allergeni più frequenti nel determinismo delle allergie respiratorie. Gli AA. hanno studiato la composizione bioatmosferica che gravita sul piccolo territorio caprese al fine di stabilire eventuale relazione tra fattori meteoclimatici e positività diagnostica allergica. I fattori meteorologici presi in esame sono stati i seguenti: precipitazioni piovose, umidità relativa, temperatura dell'aria, velocità e direzione dei venti. L'elevata umidità relativa (valori fino a 76% UR), le precipitazioni (valori fino a 108 mm), la velocità del vento (4–7 m/sec), ostacolano l'immissione e la dispersione aerea del polline delle piante anemofile diffuse sull'isola. L'elevata umidità relativa con le variazioni della temperatura (valori fino a 28,5°C) determinano, invece, il microclima caldo-umido delle abitazioni capresi, habitat ideale per lo sviluppo e la crescita degli acari Dermatophagoides. Gli AA. concludono sottolineando l'importanza di tali condizioni meteoclimatiche nel determinismo delle allergopatie respiratorie da allergeni inalanti e, particolarmente, il prevalere delle sensibilizzazioni da acari Dermatophagoides. Evidenziano inoltre come la profilassi ambientale possa rappresentare un momento fondamentale nella prevenzione dalla sensibilizzazione da acari Dermatophagoides per gli abitanti in Capri.

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Summary Spontaneous plants, particularly Parietaria and Grasses, and coltived plants, are aboundantly diffused on the Isle of Capri. Dermatophagoides mites are however the most frequent allergens that cause respiratory allergy. The AA. studied the bioatmospheric composition of the little Isle of Capri to find the possible connexion among meteoclimatic factors and allergy. The meteorological factors precipitations, relative humidity, temperature of air, speed and direction of winds, were studied. The high relative humidity (≥76%), the precipitations (≥108 mm), the speed of wind (4–7 m/sec), obstruct the dispersion of pollens of anemophilous plants. The high relative humidity and the variations of temperature (≥25°C), cause in the houses on Capri, a hot microclimate, an ideal habitat for the growth of Dermatophagoides. The AA. conclude emphasizing the importance of meteoclimatic conditions to determine the respiratory allergy caused by inhalant allergens and, particularly, the prevalence of Dermatophagoides sensitization. The AA. emphasize, moreover, that ambiental prophilaxis essential to prevent Dermatophagoides sensitization in Capri.

     

CHROOCOCCOID CYANOBACTERIA IN LAKE ONTARIO: VERTICAL AND SEASONAL DISTRIBUTIONS DURING 19821

Chroococcoid cyanobacteria (0.7–1.3 μm in diameter) were discovered to be a significant component of the Lake Ontario plankton. Using epifluorescence microscopy, the densities of these microorganisms were found to vary by four orders of magnitude with a single large peak in abundance (6.5 × 10⁵ cells mL^?1) corresponding to the time of maximum water temperature. The morphology and abundance of these cyanobacteria were similar to those previously found in oceanic systems. They constituted 10% of the bacterial numbers in the epilimnion during this period, approximately 40% of the biomass of prokaryotes less than 2.0 μm, and 30% of the biomass of all microorganisms less than 20 μm in size. Size fractionation studies indicated that they were responsible for approximately 38% of the total primary production during times of peak abundance, and were important in phosphorus uptake. Cyanobacteria observed in the food vacuoles of heterotrophic microflagellates and in the guts of rotifers suggest that the latter organisms may be important consumers of this prokaryote population.     

Downstream variations of phytoplankton in the St.Lawrence River (Québec, Canada)

Longitudinal variations of phytoplankton biomass and composition were assessed in a 250 km-long section of the St.Lawrence River, which alternately runs through narrow (< 2 km) river cross sections and wide (up to 10 km) fluvial lakes. In the main river stem, concentrations of suspended matter and total phosphorus increased with distance downstream, whereas light penetration decreased. Seasonal changes in plankton composition and biomass were more important than those resulting from differences in water mass (tributary) of origin. Sampling at three cross river sections and in two fluvial lakes showed a progressive downstream decrease in phytoplankton biomass and changes in size structure and taxonomic composition. River plankton was primarily composed of small (< 10 µm equivalent spherical diameter), truly planktonic cells belonging to Cryptophyceae and diatoms, with Chlorophyceae in summer. Plankton sampled in summer among rooted macrophytes in fluvial lakes exhibited a higher biomass of resuspended periphytic algae than in the main river stem, which contributed slightly to downstream phytoplankton biomass.Successive river cross sections always shared about 50% of their taxa, indicating a rapid downstream transport of algae within the main water mass. However, the proportion of species common to all cross sections was highest during the spring freshet, and lowest during summer low discharge, likely resulting from the development of a distinct flora in fluvial lakes during summer. Conversely, about 30% of the identified taxa were exclusive to a cross section and were replaced by others occurring downstream. Overall, phytoplankton composition along the St.Lawrence River is primarily controlled by advective forces, which result in a homogeneous flora in the main river stem, with a local contribution of resuspended periphyton from fluvial lakes.     

Seasonal variations in food quality for pelagic and benthic invertebrates in Lake Erken – the role of fatty acids

1. Plankton net samples and sedimenting matter in traps from mesotrophic Lake Erken, Sweden, were analysed for carbon (C), nitrogen (N), phosphorus (P), total lipids and fatty acid (FA) content to determine what differences and seasonal changes might exist in the quality of food available to pelagic zooplankters and benthic invertebrates. 2. Matter collected in a plankton net was assumed to correspond to food available to pelagic grazers, while matter collected in sedimentation traps provided a measure of food available to benthic invertebrates. Furthermore, food quality was assumed to be related to polyunsaturated fatty acid (PUFA) content. 3. The results suggest that suspended particulate matter, collected with a plankton net, is a much higher-quality food resource than sedimenting matter. Our data also show that only during the spring and autumn do the benthic fauna have access to high-quality food, because of the dominance of diatoms during these periods. During summer, pelagic grazer production was probably limited by food quantity, whereas benthic invertebrate production was probably limited by food quality. 4. Plankton net samples showed consistently higher values than trap samples (% of dry weight, DW, or mg g^–1 DW) for nearly all variables analysed: C, N, P, saturated FA (SAFA), monounsaturated FA (MUFA), PUFA, ω3 FA and ω6 FA. If N and P were expressed per C, the differences decreased and both data sets indicated moderate to no N or P limitation. N/P also showed well-balanced ratios throughout most of the season, on average 10 and 7 (by weight), respectively. The largest differences between the two food resources occurred in the PUFA content, including the important FA of the ω3 type. The only FA with higher levels in the trap samples were some unidentified FA of relatively short chain lengths. Seasonal variation for most variables was also very large in both net and trap samples. 5. PUFA and ω3 FA showed good relationships with the P content of net samples, but not with that of trap samples. Eicosapentaenoic acid alone did not give a good relationship with P. Thus, P seems to be a good predictor of food quality in living phytoplankton but not in dead matter or detritus.     

Research on the substances with antidotal action produced by mycetes (activity of Aspergillus fumigatus)

Riassunto La proprietà antidotica di 68 ceppi diversi di miceti é stata studiata usando come test l'inattivazione della tossina stafilococcica. Viene descritto un rapido metodo di titolazione e viene definita una unità antidotica. Sono stati trovati attivi 7 ceppi di Penicilli, 6 di aspergilli, 4 di lieviti e un ceppo diB. subtilis. La massima attività é stata trovata in un ceppo diAspergillus fumigatus. Per ottenere una maggiore produzione della sostanza attiva prodotta da questo ceppo diAspergillus fumigatus, é stata studiata l'influenza di alcuni terreni culturali e del loro pH sulla curva di produzione. Migliore terreno fu trovato il terreno di Abraham con aggiunta di idrolisato di caseina al 0,5–1%; migliore pH iniziale del terreno 4–5. Massimo di produzione si ebbe in settima giornata con pH di circa 7. La sostanza antidotica prodotta dall'Aspergillus fumigatus é distrutta dal riscaldamento per mezz'ora a 60°, ha una scarsa resistenza agli acidi e una forte resistenza agli alcali, con optimum di stabilità a pH 7, dializza solo in parte. Non é tossica, per la cavia, contrariamente a quanto é già noto non ha attività antibiotica verso lo stafilococco. L'azione sulla tossina difterica é stata pure studiata. Dopo 20 ore di contatto la sostanza diminuisce la tossicità della tossina difterica da 813 DML a 200 DML e il potere flocculante da 36 UF a 28 UF. Dopo 3 giorni di contatto la tossicità era diminuita da 400 DML a 74,5 DML e il potere flocculante diretto era scomparso. Ulteriori ricerche richiedono una purificazione del principio antidotico.

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Summary The antidotal property of 68 different strains of mycetes has been studied using as a test the inactivation of the staphilococcus toxin. A rapid method of titration is described and an antidotal unit is defined. 7 strains of Penicilli, 6 strains of Aspergilli, 4 strains of yeasts, 1 ofB. subtilis have been found to be active. The greatest activity was found for a strain ofAspergillus fumigatus. In order to get a larger production of the active substance produced by this strain ofAspergillus fumigatus, the influence of many cultural media and their pH on the production curve were investigated. The best medium was found to be Abraham's medium to which 0,5–1% of hydrolysed casein had been added, the best initial pH of medium 4–5. Maximum production was observed on the 7th day, with pH of about 7. The antidotal substance produced byAspergillus fumigatus is destroyed by heating at 60° for 1/2 hour, has a weak resistance against acids and a strong one against alkali, with optimum of stability at pH 7, dialyzes only partially. It is not toxic for guinea pigs; differently from what is already known, it has no antibiotic activity against staphilococci. The action on the diphteria toxin has been studied. After 20 hours of contact the substance diminishes the toxicity of the diphteria toxin from 813 DML to 200 DML, and the flocculation power from 36 U.F. to 28 U.F. After 3 days of contact the toxicity was decreased from 400 DML to 74,5 DML and the direct flocculation power had vanished. Further analysis demands, however, a purification of the antidotal principle.

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Ringrazio il Dott. Cavalli e l'Istituto Sieroterapico Milanese per l'aiuto ed i mezzi fornitimi durante lo svolgimento delle ricerche.     

Warming accelerates termination of a phytoplankton spring bloom by fungal parasites

Climate change is expected to favour infectious diseases across ecosystems worldwide. In freshwater and marine environments, parasites play a crucial role in controlling plankton population dynamics. Infection of phytoplankton populations will cause a transfer of carbon and nutrients into parasites, which may change the type of food available for higher trophic levels. Some phytoplankton species are inedible to zooplankton, and the termination of their population by parasites may liberate otherwise unavailable carbon and nutrients. Phytoplankton spring blooms often consist of large diatoms inedible for zooplankton, but the zoospores of their fungal parasites may serve as a food source for this higher trophic level. Here, we investigated the impact of warming on the fungal infection of a natural phytoplankton spring bloom and followed the response of a zooplankton community. Experiments were performed in ca. 1000 L indoor mesocosms exposed to a controlled seasonal temperature cycle and a warm (+4 °C) treatment in the period from March to June 2014. The spring bloom was dominated by the diatom Synedra. At the peak of infection over 40% of the Synedra population was infected by a fungal parasite (i.e. a chytrid) in both treatments. Warming did not affect the onset of the Synedra bloom, but accelerated its termination. Peak population density of Synedra tended to be lower in the warm treatments. Furthermore, Synedra carbon: phosphorus stoichiometry increased during the bloom, particularly in the control treatments. This indicates enhanced phosphorus limitation in the control treatments, which may have constrained chytrid development. Timing of the rotifer Keratella advanced in the warm treatments and closely followed chytrid infections. The chytrids' zoospores may thus have served as an alternative food source to Keratella. Our study thus emphasizes the importance of incorporating not only nutrient limitation and grazing, but also parasitism in understanding the response of plankton communities towards global warming.     

Does microbial biomass affect pelagic ecosystem efficiency? An experimental study

Bacteria and other microorganisms in the pelagic zone participate in the recycling of organic matter and nutrients within the water column. The microbial loop is thought to enhance ecosystem efficiency through rapid recycling and reduced sinking rates, thus reducing the loss of nutrients contained in organisms remaining within the photic zone. We conducted experiments with lake communities in 5400-liter mesocosms, and measured the flux of materials and nutrients out of the water column. A factorial design manipulated 8 nutrient treatments: 4 phosphorus levels × 2 nitrogen levels. Total sedimentation rates were greatest in high-N mesocosms; within N-surplus communities, 1 µM P resulted in 50% increase in total particulate losses. P additions without added N had small effects on nutrient losses from the photic zone; +2 µM P tanks received 334 mg P per tank, yet after 14 days lost only 69 mg more particulate-P than did control communities. Nutrient treatments resulted in marked differences in phytoplankton biomass (twofold N effect, fivefold P effect in +N mesocosms only), bacterioplankton densities (twofold N-effect, twofold P effects in -N and +N mesocosms), and the relative importance of autotrophic picoplankton (maximum in high NY mesocosms). Multiple regression analysis found that of 8 plankton and water chemistry variables, the ratio of autotrophic picoplankton to total phytoplankton (measured as chlorophyll ) explained the largest portion of the total variation in sedimentation loss rates (65% of P-flux, 57% of N-flux, 26% of total flux). In each case, systems with greater relative importance of autotrophic picoplankton had significantly reduced loss rates. In contrast, greater numbers of planktonic bacteria were associated with increased sedimentation rates and lower system efficiency. We suggest that different microbial components may have contrasting effects on the presumed enhanced efficiency provided by the microbial loop.Correspondence to: J. D. Wehr.     

How important is the crustacean plankton for the maintenance of water clarity in shallow lakes with abundant submerged vegetation?

• 1 We measured the abundance and biomass of filter‐feeding microcrustacean zooplankton and calculated their grazing impact on phytoplankton biomass during summer in five shallow, mesotrophic to eutrophic lakes. For three of the lakes data exist both from years with dense submerged vegetation and low turbidity (the clearwater state), as well as from years characterised by sparse vegetation and high turbidity (the turbid state). In the other two lakes data are available only for clearwater conditions.
• 2 In all lakes conditions of dense vegetation and clear water coincided with a low abundance of crustacean plankton during summer. In the three lakes that shifted, the calculated biovolume ingested by crustacean plankton (filtering rate) was 3–11 times lower during clearwater conditions compared with turbid conditions. Because phytoplankton biomass was lower during clearwater conditions, however, daily grazing pressure from microcrustacea (expressed as percentage of phytoplankton biomass) did not differ between states. In three of the five lakes, grazers were estimated to take less than 10% of the phytoplankton biomass per day, indicating filtration by zooplankton was not the most important mechanism to maintain clearwater conditions.
• 3 High densities of Cladocera were found in three of the lakes within dense stands of Charophyta. However, these samples were dominated by plant‐associated taxa that even during the night were rarely found outside the vegetation. This indicates that plant‐associated zooplankton has no major influence on the maintenance of water clarity outside the vegetation.
• 4 Spring peak abundance of Cladocera was observed in three of the lakes. In two of these, where seasonal development was studied in both the clearwater and the turbid state, spring peaks were lower during the clearwater state.
• 5 Predation, low food availability or a combination of both may explain the low zooplankton densities. Phytoplankton may be limited by low phosphorus availability in the lakes dominated by Charophyta. Our results indicate that the importance of zooplankton grazing may have minor importance for the maintenance of the clearwater state in lakes with dense, well‐established submerged vegetation.

     

Cellular growth of host and symbiont in a cnidarian-zooxanthellar symbiosis

The hydroid Myrionema ambionense, a fast-growing cnidarian (doubling time = 8 days) found in shallow water on tropical back-reefs, lives in symbiosis with symbiotic dinoflagellates of the genus Symbiodinium (hereafter also referred to as zooxanthellae). The symbionts live in vacuoles near the base of host digestive cells, whereas unhealthy looking zooxanthellae are generally located closer to the apical end of the host cell. Cytokinesis of zooxanthellae occurred at night, with a peak in number of symbionts with division furrows (mitotic index, MI = 12%-20%) observed at dawn. The MI of zooxanthellae decreased to near zero by the middle of the afternoon and remained there until the middle of the next night. Densities of live zooxanthellae living inside of host digestive cells peaked following cytokinesis, whereas densities of unhealthy looking symbionts were highest just before the division peak. Mitosis of host digestive cells was highest in the evening, also preceding the peak in zooxanthellar MI. This is the first study relating phased host cell division to diel zooxanthellar division in marine cnidarians. Food vacuoles were prevalent inside of digestive cells of field-collected hydroids within a few hours after sunset and throughout the night, coinciding with digestion of captured demersal plankton. Laboratory experiments showed that food vacuoles appeared in digestive cell cytoplasm within 2 h of feeding with nauplii of Artemia. The number and size of food vacuoles per digestive cell and the percentage of digestive cells with food vacuoles all decreased 5-7 h following feeding in laboratory experiments, and by mid-day in field-collected hydroids. Light and external food supply were important in maintaining phased division of the symbionts, with a lag in response time to both parameters of 11-36 h. Altering light and feeding during the night did not influence the level of the peak MI the next morning, though in one experiment the absence of light slowed final separation of daughter cells at the end of cytokinesis. In another experiment, hydroids starved for 3-7 d and "pulse-fed" Artemia nauplii for 1 h at the beginning of the dark period showed continued low symbiont division (< 5%) after 11 h, whether maintained in constant light or darkness, implying that most algal division is set more than 24 h prior to actual cytokinesis. Transferred to a 14:10 h light:dark cycle for another 24 h (36 h after feeding), the same hydroids exhibited a "normal" peak MI (ca. 15%) at dawn, but zooxanthellae from hydroids kept in constant darkness still showed a low MI. These results show that mitosis of symbiotic dinoflagellates requires three factors: external food; a minimum period of time following feeding (11-36 h), presumably for digestion; and a period of light following feeding, presumably to provide carbon skeletons necessary for completing cytokinesis.     

Impacts of mussel (<Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis>) farming on oxygen consumption and nutrient recycling in a eutrophic coastal lagoon

Fluxes of oxygen, nitrogen and phosphorus were determined in two areas of the Sacca di Goro lagoon, at a site influenced by the farming of the mussel Mytilus galloprovincialis and a control site. Mussel farming induced intense biodeposition of organic matter to the underlying sediments, which stimulated sediment oxygen demand, and inorganic nitrogen and phosphorus regeneration rates compared to the nearby control station. Overall benthic fluxes (–11.4 ± 6.5 mmol O₂ m⁻² h⁻¹; 1.59 ± 0.47 mmol NH₄⁺ m⁻² h⁻¹ and 94 ± 42 μmol PO₄³⁻ m⁻² h⁻¹) at the mussel farm are amongst the highest ever recorded for an aquaculture impacted area and question the belief that farming of filter-feeding bivalves has inherently lower impacts than finfish farming. In situ incubations of intact mussel ropes demonstrated that the mussel rope community was an enormous sink for oxygen and particulate organic matter, and an equally large source of dissolved inorganic nitrogen and phosphate to the water column. Overall, a one meter square area of␣mussel farm (mussel ropes and underlying sediment) was estimated to have an oxygen demand of 46.8 mmol m² h⁻¹ and to regenerate inorganic nitrogen and phosphorus at rates of 8.5 and 0.3 mmol m² h⁻¹, with the mussel ropes accounting for between 70 and more than 90% of the overall oxygen and nutrient fluxes. Even taking into account that within the farmed area of the Sacca di Goro lagoon, there are 15–20 m⁻² of open water for each one covered with mussel ropes, the mussel ropes would account for a large and often dominant part of overall oxygen and nutrient fluxes. These results demonstrate that it is essential to take into account the activity of the cultivated organisms and their epiphytic community when assessing the impacts of shellfish farming. Overall, whilst grazing by the mussel rope community could act as a top-down control on the phytoplankton, most of the ingested organic matter is rapidly recycled to the water column as inorganic nutrients, which would be expected to stimulate phytoplankton growth. Consequently, the net effect of the mussel farming on phytoplankton dynamics, may be to increase phytoplankton turnover and overall production, rather than to limit phytoplankton biomass.     

The dynamics and role of limnetic zooplankton in Loosdrecht lakes (The Netherlands)

The paper summarizes the results of a ten-year (1981–1991) zooplankton research on the Lake Loosdrecht, a highly eutrophic lake. The main cause of the lake's eutrophication and deteriorating water quality was supply up to mid 1984 of water from the River Vecht. This supply was replaced by dephosphorized water from the Amsterdam-Rhine Canal in 1984. The effects of this and other restoration measures on the lake's ecosystem were studied. Despite a reduction in the external P-load from ca. 1.0 g P m^–2 y^–1 to ca. 0.35 g m^–2 y^–1 now, the filamentous prokaryotes, including cyanobacteria and Prochlorothrix, continue to dominate the phytoplankton.Among the crustacean plankton Bosmina spp, Chydorus sp. and three species of cyclopoid copepods and their nauplii are quite common. Though there was no major change in the composition of abundant species, Daphnia cucullata, which is the only daphnid in these lakes, became virtually extinct since 1989. Among about 20 genera and 40 species of rotifers the important ones are: Anuraeopsis fissa, Keratella cochlearis, Filinia longiseta and Polyarthra. The rotifers usually peak in mid-summer following the crustacean peak in spring. The mean annual densities of crustaceans decreased during 1988–1991. Whereas seston (< 150 µm) mean mass in the lake increased since 1983 by 20–60%, zooplankton (> 150 µm) mass decreased by 15–35%.The grazing by crustacean community, which was attributable mainly to Bosmina, had mean rates between 10 and 25% d^–1. Between 42 and 47% of the food ingested was assimilated. In spring and early summer when both rotifers and crustaceans have their maximal densities the clearance rates of the rotifers were much higher. Based on C/P ratios, the zooplankton (> 150 µm) mass contained 2.5 times more phosphorus than seston (< 150 µm) mass so that the zooplankton comprised 12.5 % of the total-P in total particulate matter in the open water, compared with only 4.5% of the total particulate C. The mean excretion rates of P by zooplankton varied narrowly between 1.5 and 1.8 µg P 1^– d^–1, which equalled between 14 and 28% d^–1 of the P needed for phytoplankton production.The lack of response to restoration measures cannot be ascribed to one single factor. Apparently, the external P-loading is still not low enough and internal P-loading, though low, may be still high enough to sustain high seston levels. Intensive predation by bream is perhaps more important than food quality (high concentrations of filamentous cyanobacteria) in depressing the development of large-bodied zooplankton grazers, e.g. Daphnia. This may also contribute to resistance of the lake's ecosystem to respond to rehabilitation measures.     

Carbon dynamics in an ultra-oligotrophic epishelf lake (Beaver Lake, Antarctica) in summer

1. Microbial plankton dynamics in an ultra‐oligotrophic epishelf lake (Beaver Lake, Antarctica) were investigated over an austral summer (December 2002 to January 2003). The aim was to characterise carbon cycling in an environmentally extreme lake. 2. The lake had an unusual temperature profile with peak temperatures of 1.3–1.9 °C between 20 and 25 m. Photosynthetically active radiation penetrated to the lake bottom (110 m) on occasions. The ice cover underwent marked thinning and melting during the study period. 3. Chlorophyll a concentrations were consistently low, usually below 1 μg L^?1, with highest concentrations close to the lake bottom, where the photosynthetic elements showed strong autofluorescence. Mean photosynthetic nanoflagellates ranged between 34.9 × 10⁴ L^?1 ± 33.5 (23rd December) and 130.9 × 10⁴ L^?1 ± 112.3 (4th December). Highest photosynthetic activity was usually recorded below 25 m. Rates of carbon fixation varied between 0.089 μg C L^?1 h^?1 ± 0.002 and 0.579 μg C L^?1 h^?1 ± 0.156. Primary production was limited by low temperature and orthophosphate availability. 4. Mean bacterial concentration throughout the water column ranged between 9.3 × 10⁷ L^?1 ± 1.2 (23rd December) and 14.0 × 10⁷ L^?1 ± 1.8 (28th January). Bacterial production was low, less than 10% of primary production and ranged between 2.1 ng C L^?1 h^?1 ± 0.8 and 12 ng C L^?1 h^?1 ± 0.9. Highest rates coincided with times of highest primary production. On occasion dissolved organic carbon (DOC) concentrations dropped to 20 μg L^?1, probably below accurate limits of detection, suggesting that carbon substratum and phosphorus may have limited bacterial growth. 5. Heterotrophic nanoflagellates varied significantly over the summer from a mean of 26.6 × 10⁴ L^?1 ± 14.2 (23rd December) to 133.8 × 10⁴ L^?1 ± 33.5 (14th December). They imposed a significant grazing impact on the bacterioplankton, removing in excess of 100% of bacterial production in December. 6. The total organic carbon pool [DOC and particulate organic carbon (POC)] was below 600 μg L^?1. The ratio of DOC : POC ranged between 0.44 : 1 and 2.8 : 1 in the upper 40 m of the water column, and 1.8 : 1 and 3.7 : 1 in the lower waters. The microbial plankton contributed 1–29% of POC, thus detrital POC made up the largest fraction of the POC pool. 7. Beaver Lake is an extreme lacustrine ecosystem where heterotrophic processes occasionally appear to be carbon limited. Significant summer ice‐melt, not seen in a previous opportunistic sampling, may be having an impact on the carbon cycle.