Water relations of Picea abies. II. Determination of the apoplastic water content and other water relations parameters of needles by means of capillary microcryoscopy and the pressure-volume

Using the pressure volume analysis (PV analysis) on the shoots of Norway spruce (Picea abies [L.] Karst.) and the here presented capillary microcryoscopy of the needle press sap of the same shoots, it was possible to determine the amount of apoplastic water in the needles (W_an) as well as in the defoliated shoots (W_as). Additionally, the bulk osmotic pressure at full water saturation in the symplast of the needles and defoliated shoots (π_on and π_os) was determined. The dependence of the bulk-averaged turgor pressure (P_t) on the water content and the relationship between the bulk modulus of elasticity of the needles (?_n) and the bulk-averaged needle turgor pressure (P_tn) was shown with help of the PV analysis on the whole shoots and defoliated shoots. The study was conducted at the end of the vegetation period in 1987 and during winter 1988. The proportion of W_an in the total needle water content (W_tn) was 14% in September 1987 and 12.5% in March 1988. The respective percentage of W_as in W_ts were 27% and 25%. The amount of apoplastic water depended on the ratio of the dry weight of defoliated shoots to the dry weight of the whole shoots. A standard mean value for the amount of W_an in the total water content of the shoots (W_t) was therefore not possible. The bulk osmotic pressure at full water saturation in the needle symplasts was –1.9 MPa in September 1987 and –2.2 MPa in winter 1988. The respective values of the bulk osmotic pressures in the symplast of the defoliated shoots (π_os) were –1.5 MPa and –1.7 MPa. Thus π_on was 0.1 MPa lower and π_os 0.3–0.4 MPa higher than the average osmotic pressure during full water saturation in the symplast of the whole shoots (π_o). The relation between bulk-averaged turgor pressure and water content showed that during water loss P_tn dropped more rapidly than the turgor pressure of defoliated shoots (P_ts). Consequently the needles were less elastic than the defoliated shoots. The turgor values of whole shoots followed an intemediate course between P_tn and P_ts. The flat course of P_ts seems to be the main reason for the often observed “plateau” of ψ-isotherms of whole shoots near full turgor.     

Noninvasive assessment of cardiac contractility by using (dP/dt)/P of carotid artery pulses during exercise

In earlier studies we have shown that both the pressure (P) of the carotid artery pulse (CAP) and its first derivative (CAP dP/dt) could be recorded during moderate exercise. To establish that the CAP (dP/dt)/P is a noninvasive substitute for the left ventricular (LV) value, LV (dP/dt)/P, an index of cardiac contractility, we studied CAP (dP/dt)/P under various states of activity in the autonomic nervous system in 12 healthy male subjects. Increased sympathetic nerve activities yielded by passive tilting, emotional load, or cold stress increased CAP (dP/dt)/P significantly (P< 0.05). Increased parasympathetic nerve activity by ocular compression, however, did not significantly affect the value. Moderate exercise at a heart rate of approximately 150 beats·min^–1 increased it significantly from 16.7 to 25.2·s^–1 in a supine position (P<0.001) and from 16.6 to 24.8·s^–1 in an upright position (P<0.001). It increased monotonically as heart rate increased, but the slope was steeper when the heart rate was greater than approximately 100 beats·min^–1 than it was when the rate was less than 100 beats·min^–1. In conclusion, the present study indicated that CAP (dP/dt)/P can be used as a noninvasive index of cardiac contractility even in moderate exercise.     

Experimental study of 60Co behaviour in Tejo River sediments

The objective of this study was to obtain information on the transfer of radiocobalt in freshwater environments that can be used to predict its environmental distribution. The sediment-water behaviour of ⁶⁰Co in freshwater systems was studied through adsorption and desorption experiments undertaken using sediments and water from Fratel Reservoir in the Tejo River. The suspended sediment concentrations (C_s: 500–2000 mg 1^–1) and Co distribution coefficient (K_d) were inversely related: K_d = 2211–2001 ln [C_s]; K_d ranged from 4000 to 8000 ml g^–1. With a suspended sediment concentration of 1000 mg 1^–1, the ⁶⁰Co concentration remaining in solution (C_t) was given by: C_t = 49.4 e^–0.584t + 46.3 e^–0.014t; where t is the time in days and the half-life periods are 1.2 and 50 days. In a closed system, desorption of ⁶⁰Co could be described by a one-component relation with a half-life of 104 days, and a two component relation (half-life 5 hours and 45 days) in an open system. In river water the ⁶⁰Co was found to be almost 100% in cationic forms, however, in the presence of sediment there was a decrease in the proportion of cationic forms (to 50%), with some anionic forms appearing.     

Minimum evolution using ordinary least-squares is less robust than neighbor-joining

The method of minimum evolution reconstructs a phylogenetic tree T for n taxa given dissimilarity data d. In principle, for every tree W with these n leaves an estimate for the total length of W is made, and T is selected as the W that yields the minimum total length. Suppose that the ordinary least-squares formula S _W (d) is used to estimate the total length of W. A theorem of Rzhetsky and Nei shows that when d is positively additive on a completely resolved tree T, then for all W ≠ T it will be true that S _W (d) > S _T (d). The same will be true if d is merely sufficiently close to an additive dissimilarity function. This paper proves that as n grows large, even if the shortest branch length in the true tree T remains constant and d is additive on T, then the difference S _W (d)-S _T (d) can go to zero. It is also proved that, as n grows large, there is a tree T with n leaves, an additive distance function d _T on T with shortest edge ε, a distance function d, and a tree W with the same n leaves such that d differs from d _T by only approximately ε/4, yet minimum evolution incorrectly selects the tree W over the tree T. This result contrasts with the method of neighbor-joining, for which Atteson showed that incorrect selection of W required a deviation at least ε/2. It follows that, for large n, minimum evolution with ordinary least-squares can be only half as robust as neighbor-joining.     

Adsorption Characteristics and the Effect of Dissolved Organic Matter on Mercury(II) Adsorption of Various Soils in China

To evaluate the adsorption characteristics and effects of dissolved organic matter (DOM) from wheat straw (DOM_W) and swine manure (DOM_S) on mercury [Hg(II)] adsorption by soils, a series of experiments was conducted on 26 soils with different soil properties.Results showed that the values of K_d (a solid–liquid partition coefficient) of soils varied within a range of 0.768–14.386 L g^?1. K_d values were mainly controlled by soil organic matter (SOM), cation exchange capacity (CEC), soil nitrogen (N), and soil sulfur (S). When DOM_W and DOM_S were added to the soil samples, the amount of Hg(II) adsorbed by the soils decreased significantly. Furthermore, based on the decreased percentage of adsorption of Hg(II) by soil upon adding DOM_W (P_DOMW) or DOM_S (P_DOMS), about 73.08% soils, the values of P_DOMS were smaller than those of P_DOMW. The P_DOMW values were related to SOM, pH, free Fe oxide content, and CEC, whereas P_DOMS values were related to soil free Fe/Al oxide contents. Therefore, we should pay more attention about mercury risk caused by the addition of exogenous organic matter in soils, especially for the soils with low or high pH, less SOM, low CEC, and less free Fe/Al oxide.     

Acute modulation of myocardial function by angiotensin 1–7

Angiotensin 1–7 is a bioactive heptapeptide of the renin–angiotensin system. Its cardiovascular actions have recently acquired growing relevance, mainly due to its counter-regulatory actions in the angiotensin cascade. The aim of the present study was to evaluate the actions of angiotensin 1–7 on myocardial function. Increasing concentrations of angiotensin 1–7 (10⁻⁹ to 10⁻⁵ M) were added to rabbit right papillary muscles: (1) in baseline conditions with intact endocardial endothelium (EE); (2) after selective removal of the EE with Triton X-100 (1 s, 0.01%); (3) with intact EE in the presence of the Mas receptor antagonist A-779, the AT₁ receptor antagonist ZD-7155, the AT₂ receptor antagonist PD-123,319 or the nitric oxide synthesis inhibitor NG-nitro-l-arginine (l-NA). Concerning the effects on contractility, we observed a significant decrease on active tension, dT/dt_max, peak shortening and dL/dt_max of −10.5 ± 3.6%, −8.0 ± 3.0%, −5.3 ± 2.6% and −5.7 ± 2.3%, respectively. There was no change on relaxation parameters, namely dT/dt_min or dL/dt_min. Time to half relaxation was significantly decreased. The presence of ZD-7155 or PD-123,319 did not change these effects. However, angiotensin 1–7 effects on myocardial properties were abolished after selective EE removal and in the presence of A-779 or l-NA. In conclusion, in this animal species, angiotensin 1–7 through its binding to Mas receptor induces a negative inotropic effect modulated by the EE and nitric oxide and independent of AT₁ or AT₂ receptors activation. As the effects described in the present work were influenced by the endocardial endothelium, they may be disrupted in situations associated to endothelial dysfunction, as in heart failure or myocardial ischemia.     

Genetic analysis of neonatal death with growth retardation in F1 male Dh/+ mice

Nearly all F₁ male mice with Dh/+ genotype between DDD female and DH–Dh/+ male die within a few days after birth; however, this is not observed in the reciprocal cross. The F₁ Dh/+ males usually exhibit growth retardation prior to death. To identify the putative genetic locus or loci in DDD genome that cause the abnormalities in the presence of the Dh, a linkage analysis was carried out in backcross progeny of a cross of (DDD female × DH–+/+ male) F₁ female × DH–Dh/+ male. Appearance of growth retardation was examined from the day of birth, and both growth-retarded and normally weaned Dh/+ males were genotyped for microsatellite marker loci spanning autosomes and the X Chromosome (Chr). Significant evidence for linkage was identified on the distal edge of the X Chr, near the microsatellite marker of DXMit135. Furthermore, among mice from DDD female × reciprocal F₁ Dh/+ male produced between DH–Dh/+ and progenitor strains (C57BL/6J, C3H/HeJ and BALB/cA), only the progeny from ♀DDD ×♂(♀DH–Dh/+×♂C3H/HeJ) F₁ Dh/+ male did not show any lethality and/or growth retardation. Thus, the lethality in F₁ Dh/+ males accompanied by growth retardation is caused by the interactions between the Dh gene, X Chr, and Y Chr. Based on the CAG repeat sequence length polymorphism among Mus musculus musculus Sry gene, C3H/HeJ was different from C57BL/6J, BALB/cA, and DH. These data suggest that there are at least two functional types of Y Chr in Mus musculus musculus. Received: 22 January 1999 / Accepted: 5 April 1999     

Minimal oxygen consumption and optimal contractility of the heart: Theoretical approach to principle of physiological control of contractility

Oxygen consumption of the left ventricle (MVO ₂) was evaluated theoretically under the condition that the ventricle pumps a constant stroke volume against a constant arterial pressure, hence producing a constant external mechanical stroke work, with a widely varied contractility.MVO ₂ was calculated by an empirical equation which had been inferred previously. Theoretical results indicated that the ventricle has a contractility at whichMVO ₂ is minimal in spite of constant external work and therefore the mechanical efficiency as a pump is maximal. Such a contractility can be considered to be optimal from a standpoint of metabolic economy. The optimal contractility fell within the physiological range of contractility which had been observed experimentally. The result suggests a possibility that the contractility of a normal heart might be physiologically adapted to such an optimal level.     

Modeling population dynamics of yeast-like symbionts (Ascomycota: Pyrenomycetes: Clavicipitaceae) of the planthopper <Emphasis Type="Italic">Delphacodes kuscheli</Emphasis> (Hemiptera: Delphacidae)

Delphacodes kuscheli establish mutualistic relationship with yeast-like symbionts (YLS) that live in the fat body and are necessary for host survival and reproduction. We estimated for a host of age t, its body weight, W_(t), and the number of YLS per host, YLS_(t). The host body weight was calculated as: W_(t)?=?Lm/[1+ e ^(d–kt)], (Lm?=?the maximum observed weight, and d and k are constants), and the fat body was considered a fixed proportion of W_(t). We calculated the number of YLS per unit host body mass: α_(t)?=?YLS_(t)/W_(t). We also calculated the number of YLS per host, cYLS_(t), and analyzed the pattern of variation in both sexes adapting the expression of the logistic model: cYLS_(t)?=?KN_oe^rt/K+(e^rt -1)N_o, (N_o?=?initial number of YLS, r?=?intrinsic per capita rate of natural increase, and K?=?variable carrying capacity). In females the carrying capacity varied according to a constant proportion of the host’s weight: K_(t)?=?αW_(t). In males α_(t) was considered a decreasing function of the host age: K_(t)?=?α_(t)W_(t). The coefficients No, α, and r were subjected to parameterization. We found that the patterns of W_(t) and YLS_(t) of D. kuscheli were similar to other planthoppers. In females YLS increased up to the adult stage and then remained almost constant, varying similarly to individual weight. In males YLS increased up to the 5th instar nymph as the individual weight did, but the number of YLS decreased in the adult stage and the correlation was not so good. The calculated number of YLS per host matches reasonably well with the number estimated experimentally both in females and males. This is the first study that quantified and modeled the dynamics of YLS endosymbionts in a Neotropical planthopper pest. The models will be used in future studies for better understand the experimental reduction of YLS in young nymphal stages.     

Effects of training for two ball games on the saliva response of adrenocortical hormones to exercise in elite sportswomen

In a group of 20 elite female handball or volleyball players, an evaluation was made of the response to a 4-month training period of cortisol, androstenedione and dehydroepiandrosterone in the saliva. At the beginning of the training programme (W₁) and at the 7th (W₇) and 16th weeks (W₁₆), hormone concentrations were measured on awakening (8 a.m.; resting samples), and also before (t ₀) and at the end (t ₁₂₀) of a 2-h exercise session (simulated match) which took place at 6 p.m. The training programme increased the concentrations of adrenal androgens in the saliva at rest (P<0.05) for both groups of subjects, with no change being noted in cortisol concentrations. In contrast, amongst the volleyball players, stressful stimuli produced by an increase in the amount of training did not affect adrenocortical metabolism during exercise. Indeed, a simulated volleyball match resulted in a decrease in salivary cortisol (P<0.05) and androgen concentrations (P<0.05) without regard for the week chosen for the test investigations. In contrast, a simulated handball match caused an increase in cortisol concentrations at W₁ only (P<0.05), with no change in the adrenal androgens concentration in any week of the training programme. The regulators of these hormones during a period of exercise and during the course of a training programme would seem to be different. Accepted: 30 October 1997     

Life history traits of Aphanius ginaonis Holly, 1929 (Cyprinodontidae) and potential risks of extinction in the Geno hot spring (Iran) population

This study presents some traits of the Aphanius ginaonis life history in the Geno hot spring and explains the potential risks of its extinction. Sampling was from March 2009 to February 2010. A total of 61 males and 71 females were measured (total length) and weighed, with data on reproductive biometry also taken. Growth parameters were determined in addition to weight–length relationships: W (t) = 0.012TL^3.42, R² = 0.96 for females and W (t) = 0.0101TL^3.38, R² = 0.94 for males. A. ginaonis females showed an asymptotic total length (TL_∞) of 53.03 mm; the growth coefficient, K (year^?1) 0.15, t₀ (year) 1.01; and natural mortality coefficient M (year^?1) 0.62. In males the value for TL_∞ was 48.83 mm; for K (year^?1) 0.2, t₀ (year) 0.44; and M (year^?1) 0.49. The relationship between absolute fecundity and fish size (total length, body weight or age) showed a strong correlation to body weight. The A. ginaonis population is threatened with extinction – and a co‐management in cooperation with the local population for strong protection measures is urgently needed.     

Relationship between Number of Eggs,Brood Weight,and Female Body Weight in Crustacea

Relationships between number of eggs (N_g), brood weight (W_g), and body length (L) and weight (W) of females were studied for 16 orders and suborders of Crustacea. The study was based on the authors' observations in the inland waters of the European USSR, in the coastal regions of the fareastern and northern seas and data from V. V. KUZNETSOV (preserved in archives). An extensive literature was also used. The equations describing the relationships (N_g=f(L) and W_g=f(W) are calculated for some species and high taxons. On the average for the superclass (excluding the order Notostraca) the W_g/W ratio appeared to be 0.16. This ratio is markedly different for species of Notostraca. It is supposed that this difference is due to the high metabolic rate of Notostraca.     

Study of the impact of intramyocardial implantation of stem cells on myocardial perfusion and contractility in patients with coronary heart disease concurrent with postinfarct cardiosclerosis and chronic heart failure

OBJECTIVE: to study of intramyocardial implantation of cultured bone marrow stem cells on myocardial perfusion and contractility in the surgical treatment of patients with coronary heart disease (CHD) and chronic heart failure (CHF), by synchronized single-photon emission computed tomography (SSPECT) of the myocardium. SUBJECTS AND METHODS: The study included 11 patients. Intramyocardial injection of cell injections into the myocardial periscarring areas was made at coronary bypass surgery. All the patients underwent 99mTc myocardial SSPECT MIBI before and 3, 6, 12 months after surgery. RESULTS AND CONCLUSIONS: Implantation of bone marrow stem cells into the left ventricular myocardium favorably affects left ventricular remodeling and contributes to the improvement of myocardial perfusion and contractility, as evidenced by 99mTc.     

Resource dynamic plays a key role in regional fluctuations of the spruce bark beetles Ips typographus

Abstract 1 We analysed time series of spruce bark beetles (N_t) caught in pheromone traps from 1979 to 2000 in approximately 100 localities throughout south‐east Norway. 2 The analysis was performed at two spatial scales (whole area and 12 subregions), and included additional analyses of the time‐series sequences before and after a large windfelling (1987) that appeared to induce a shift in the dynamics. 3 Regression of R_t (logarithmic per‐capita growth rate) on N_{t ? d} indicated that the endogenous dynamics were dominated by lag 1 density dependence. This was particularly so in the sequence after the large windfelling (R² = 0.79), probably due to intraspecific competition for breeding substrate. 4 The sequence before the windfelling (1979–1987) was declining without significant density dependence. We suggest this to be a transition period, reflecting a drop in carrying capacity due to depletion of susceptible trees during the preceding outbreak period (1970s) and a drop in beetle number to below the density required to kill trees. 5 Windfelling (W_{t ? 1}) appears to be an important predictor of the dynamics; however, it was difficult to evaluate the statistical significance of this factor due to only one large windfall event. 6 The weak influence of drought stress (D_{t ? 1}) could be due to the absence of severe drought periods within the time series.     

Intrinsic water‐use efficiency of temperate seminatural grassland has increased since 1857: an analysis of carbon isotope discrimination of herbage from the Park Grass Experiment

A 150‐year‐long record of intrinsic water‐use efficiency (W_i) was derived from community‐level carbon isotope discrimination (¹³Δ) in the herbage of the unfertilized, unlimed control treatment (plot 3) of the Park Grass Experiment at Rothamsted (England) between 1857 and 2007. ¹³Δ during spring growth (first cut harvested in June) averaged 21.0‰ (±0.5‰ SD) and has not shown a long‐term trend (P=0.5) since 1857. ¹³Δ of summer/autumn growth (second cut harvested between September and November) increased from 21.3‰ to 22.0‰ (P < 0.001) between 1875 and 2007. W_i during spring growth has therefore increased by 33% since the beginning of the experiment, and W_i of summer/autumn growth has increased by 18%. The variation in ¹³Δ was mainly related to weather conditions. Plant available soil water explained 51% and 40% of the variation in spring growth ¹³Δ and summer/autumn growth ¹³Δ, respectively. In the 1857–2007 period yields have not increased, suggesting that community‐level photosynthesis has not increased either. Therefore, the increased W_i probably resulted from a decreased stomatal conductance. Vapour pressure deficit (VPD) during spring growth (March–June) has not changed since 1915, meaning that instantaneous water‐use efficiency (W_t) in spring time has increased and transpiration has probably decreased, provided that leaf temperature followed air temperature. Conversely, VPD in the months between the first and second cut has increased by 0.07 kPa since 1915, offsetting the effect of increased W_i on W_t during summer and early autumn. Our results suggest that vegetation has adjusted physiologically to elevated CO₂ by decreasing stomatal conductance in this nutrient‐limited grassland.     

Attenuation of Post-ischemia Reperfusion Injury by Thaliporphine and Morphine in Rat Hearts

Summary Pretreatment with thaliporphine before ischemia affords cardioprotective effects against reperfusion injury via antioxidant activity. This study evaluated whether thaliporphine administered at a certain period after myocardial ischemia conferred the same cardioprotection and assessed its possible new mechanism. The left main coronary artery of anaesthetized rats was occluded for 1 h and then reperfused for 2 h. Thaliporphine was administered at 10 min before reperfusion. Controls received saline only. Morphine, a nonselective opioid receptor agonist, was used as reference compound at 0.3 mg/kg. Thaliporphine at 0.05 and 0.5 mg/kg were found to reduce the infarct size. Recovery of cardiac function was higher in thaliporphine (0.5 mg/kg) group, as assessed by a significant improvement in the rates of pressure development (+dp/dt _max). This compound also reduced plasma creatine kinase and cardiac MPO activity. These protective effects afforded by thaliporphine were diminished by the opioid receptor antagonists (naloxone or naltrexone) and by the mitochondrial K_ATP blocker 5HD. In comparison, morphine reduced infarct size and MPO activity in the myocardium but produced slightly improvement in cardiac function after ischemia-reperfusion. These results demonstrate that reperfusion therapy with thaliporphine protect cardiac injury through further mechanism via activation of opioid receptor and opening of mitochondrial K_ATP channels as morphine but with stronger activity.     

Mesenchymal stem cells conditioned with glucose depletion augments their ability to repair-infarcted myocardium

Mesenchymal stem cells (MSCs) are an attractive candidate for autologous cell therapy, but their ability to repair damaged myocardium is severely compromised with advanced age. Development of viable autologous cell therapy for treatment of heart failure in the elderly requires the need to address MSC ageing. In this study, MSCs from young (2 months) and aged (24 months) C57BL/6 mice were characterized for gene expression of IGF‐1, FGF‐2, VEGF, SIRT‐1, AKT, p16^INK4a, p21 and p53 along with measurements of population doubling (PD), superoxide dismutase (SOD) activity and apoptosis. Aged MSCs displayed senescent features compared with cells isolated from young animals and therefore were pre‐conditioned with glucose depletion to enhance age affected function. Pre‐conditioning of aged MSCs led to an increase in expression of IGF‐1, AKT and SIRT‐1 concomitant with enhanced viability, proliferation and delayed senescence. To determine the myocardial repair capability of pre‐conditioned aged MSCs, myocardial infarction (MI) was induced in 24 months old C57BL/6 wild type mice and GFP expressing untreated and pre‐conditioned aged MSCs were transplanted. Hearts transplanted with pre‐conditioned aged MSCs showed increased expression of paracrine factors, such as IGF‐1, FGF‐2, VEGF and SDF‐1α. This was associated with significantly improved cardiac performance as measured by dp/dt_max, dp/dt_min, LVEDP and LVDP, declined left ventricle (LV) fibrosis and apoptosis as measured by Masson's Trichrome and TUNEL assays, respectively, after 30 days of transplantation. In conclusion, pre‐conditioning of aged MSCs with glucose depletion can enhance proliferation, delay senescence and restore the ability of aged cells to repair senescent infarcted myocardium.     

Theory of transport in linear biological systems: I. Fundamental integral equation

The conditions under which the output,γ _b (t), of a biological system is related to the input,γ _a (t), by an integral equation of the typeγ _b (t) = ∫ ₀ ^t γ _a (ω)w(t−ω)dω, where ω(t) is a transport functioncharacteristic of the system, are analyzed in detail. Methods of solving this type of integral equation are briefly discussed. The theory is then applied to problems in tracer kinetics in which input and output are sums of exponentials, and explicit formulae, which are applicable whether or not the pool is uniformly mixed, are derived for “turnover time” and “pool” size.     

Asymptotic theory for analyzing dose-response survival data with application to the low-dose extrapolation problem

A model of the form P(t, d)=1−;exp{-(t)σ^K_i=0q_idⁱ}, q_i 0, is proposed for analyzing dose-response survival data with right censoring. The q_i's in the dose polynomial are estimated by maximizing the Cox partial likelihood, and given these estimates. Λ(t) is estimated nonparametrically by an estimator proposed by Breslow. Large-sample properties of these estimators are established. Estimates and related large-sample properties are provided for the “virtually safe dose” and other parameters for assessing low-dose carcinogenic risk as a function of age, using data from animal carcinogenesis experiments.     

Flow properties of high-molecular-weight DNA solutions: viscosity, recoil, and longest retardation time

Viscosity η, recoil Γ, and longest retardation time τ_1R were measured for buffered aqueous solution of T2 DNA (M = 1.3 × 10⁸) and cell lysattes of Bacillus subtiles W23 (DNA M = 2 × 10⁹) as a function of concetration, shear stress σ, and time of shear t, using a cartesian-diver-suspended couette flow system. For the T2 solution, η decreased with increasing σ, Γ(t) going through a maximum with t. For the B. subtiles lysates, the preponderant rheological component of which is chromatin DNA, above a critical σ, the η, Γ(t), and τ_1R increased t over 15 to 45 minutes duration to values up to several times larger, indicating the formation of intermolecular aggregates. The onset of such effects and their significance in th e measurement of molecular properties by hydrodynamic means is disscussed.