Efficacy of Monensin Against Bovine Coccidiosis in Young Holstein-Friesian Calves*

Monensin, an anticoccidial antibiotic, was incorporated into pelleted feed and given to 10-week-old Holstein-Friesian calves at 0.25 mg/kg, 1.0 mg/kg, or 2.0 mg/kg of body weight. Inoculated calves were inoculated by drenching with 500,000 sporulated oocysts of Eimeria bovis. Other calves served as inoculated or uninoculated controls. Observations were recorded on oocyst discharge in the feces, clinical signs, weight gain, food consumption, hemoglobin, packed cell volume, total serum protein, sodium and potassium content of the serum, and differential white cell counts. Calves in the inoculated control group developed severe infections, discharged large numbers of oocysts, developed clinical signs and 1 of 5 died. Uninoculated, untreated control calves were essentially free of coccidia. A few calves in the groups which received monensin developed light infections but none of them had clinical signs of coccidiosis. Calves which received the highest and the lowest dosages of monensin gained weight less rapidly than did the uninoculated controls or the animals which received monensin at 1.0 mg/kg of body weight. Inoculated control calves with severe infections had reduced food intake and a significant reduction in weight which was not regained during the experimental period. The only other significant change in any of the parameters measured was a reduction in the total serum protein of inoculated, nonmedicated control calves. The level returned to normal 5 weeks after clinical signs first appeared.     

Plasmodium berghei NK65 in the Inbred A/J Mouse: Immunity in the A/J Mouse Naturally Recovered from NK65C and Challenged with NK65E*

SYNOPSIS. Female retired breeder A/J mice were infected with Plasmodium berghei NK65C deme. Those animals which recovered were allowed to recrudesce and were inoculated again with NK65C. Twenty-one weeks after the original challenge, the mice were divided into 2 equal groups. One group was challenged with NK65C and the other with NK65E. Both demes of P. berghei were mosquito derived from NK65. NK65C appeared to give less protection to mice challenged with NK65E deme than to those challenged with the homologous NK65C deme. One mouse which had recovered from infection with NK65C deme died from the NK65E challenge. No definitive conclusions could be drawn regarding antigenic variation and virulence between demes E and C.     

Cooling as Reinforcing Stimulus in Aplysia

An experiment was carried out to investigate the role of temperaturein the previously reported reinforcing effect of an increasein sea water level in Aplysia. In the present experiment, itwas found that the reinforcing effect of water level changeon rod-pressing behavior in Aplysia depends on a decrease intemperature associated with water level change. In order studymodification of rod pressing behavior produced by contingentincrease in water level and decrease in temperature, the rateand latency of rod-press responses in experimental animals wherecompared with those of yoked control animals exposed to non-contingentwater level and temperature change. Higher response rates andshorter response latencies were obtained from experimental overyoked control animals but only the shorter latencies of experimentalanimals were attributed to a behavioral change resulting fromcontingent water level and temperature reinforcement.     

Efficacy of Monensin or Amprolium in the Prevention of Hepatic Coccidiosis in Rabbits

SYNOPSIS. New Zealand White rabbits were fed monensin (Coban® Premix) or amprolium in pelleted feed as a prophylaxis against infection with Eimeria stiedai. Rabbits receiving monensin at 0.005, 0.01, or 0.02% concentrations in the feed did not become infected but ate only small amounts of pellets when the drug concentration was 0.02%. All rabbits given 0.02% amprolium in pelleted feed developed severe infections. Rabbits on "limited" (8 gm pellets per day) diets were susceptible to infection.     

Fine Structural Observations of the Erythrocytic Stages of Plasmodium chabaudi Landau, 1965*

SYNOPSIS. Electron microscopic examination of Plasmodium chabaudi in mouse erythrocytes revealed many characteristics resembling those observed in other mammalian malarial parasites. A double unit membrane surrounds the trophozoite cytoplasm which contains many ribonucleoprotein particles, a limited amount of endoplasmic reticulum and membraned organelles including sausage-shaped vacuoles and multilaminated membraned bodies. More or less circular double membraned vacuoles, possibly cross sections of the sausage-shaped vacuoles, are common. Typical protozoan mitochondria are lacking. The limiting membrane of the merozoites is triple-layered. Paired organelles and small dense bodies are found in the merozoites along with dense granular masses in the nuclei. Trophozoites have cytostomal structures as well as invaginations of the plasma membrane at sites where no cytostomes are evident. Digestion appears to occur in single membrane-bound vesicles which contain one to several pigment grains. P. chabaudi frequently contains multiple food vacuoles and has polymorphism manifested in part by the presence of cytoplasmic extensions and of nuclei with a variety of shapes. Several apparently free forms are noted, often accompanied by a thin rim of host cytoplasm. “Appliqué” forms are common among the trophozoites as are forms in which 2 or more trophozoites are joined together. Finally, alterations in the host cytoplasm resembling the socalled Maurer's clefts are frequent. Ferritin-containing vacuoles also appear in the host cell.     

Effects of Light, pH, Temperature, and Crowding on Megaspore Germination and Sporophyte Formation in Marsilea

Megaspore germination and sporophyte formation of Marsilea vestitaH. and G. was studied under different light, pH, temperature,and crowding conditions during a 6 d experimental period. Maximumgermination and sporophyte development occurs under relativelylow light intensity. Darkness and high light intensity inhibitsporophyte development. Selected wavelengths of light (red,far-red, green, blue) and darkness reduce both megaspore germinationand sporophyte development as compared to white light. Megasporesand sporophytes show maximum development at 25 ?C in light,whereas their development is reduced at all temperatures indarkness. The optimum pH range for megaspore germination ispH 7–8 and that for sporophyte development is pH 7. Sporocarpcontents alter the pH of unbuffered acidic and basic media towarda more optimal growth condition (pH 6–8) for megasporegermination. Megaspore germination and sporophyte developmentvary inversely with conditions of crowding. Root and leaf growthon developed sporophytes is very similar in most treatments.     

Ultrastructure of an Unusual Erythrocytic Form of Plasmodium berghei*

SYNOPSIS. Unusual dense forms were discovered in ultrathin sections of Plasmodium berghei-infected rat erythrocytes. These parasites frequently occurred with one or more typical trophozoites in a single blood cell. They appeared darker than both the neighboring trophozoites and the host erythrocyte. Ribosomes were visible in clusters in their compact cytoplasm. The endoplasmic reticulum, when present, had dilated cisternae often containing a material of low density. Large food vacuoles werecommonly seen along with the small vesicles harboring pigment granules. The single large nucleus had dense nucleoplasm. Multilaminated membraned bodies and sausage-shaped vacuoles were, seen in some of the parasites. The exact identity of this form of P. berghei is not known. Its possible significance is discussed with particular reference to the differentiation of gametocytes.