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At least 91 records · Page 5Linked to original sources
PubMed1954

Reversible inactivation of typhus Rickettsiae. I. Inactivation by freezing.

Rickettsiae that have been frozen and thawed in isotonic salt solutions show greatly decreased toxicity for mice, hemolytic activity, respiration, and infectivity for eggs. All these properties can be partially restored by incubation of the rickettsiae in the presence of DPN and coenzyme A for 2 hours at 34 degrees C. The extent of both inactivation and of subsequent reactivation is markedly affected by the presence of low concentrations of sucrose during the process of freezing and thawing. It has been shown that DPN is present in rickettsial suspensions and that in preparations that have not been frozen, the DPN sediments with the rickettsiae. After freezing in isotonic salt solution the DPN becomes non-sedimentable.

Animals↗
PubMed1956

Studies on the effects of subzero temperatures on the viability of spores of Aspergillus flavus. I. The effect of rate of warming.

1. The survival of spores of Aspergillus flavus suspended in distilled water and cooled rapidly to -70 to -75 degrees C. was found to depend primarily on the rate of subsequent warming of the frozen suspension. Only 7 per cent of the spores germinated following slow warming at 0.9 degrees C. per minute, whereas about 75 per cent germinated following rapid warming at 700 degrees C. per minute. 2. Viability was dependent on the rate at which the suspensions warmed from -70 to 0 degrees C. (subzero warming), but was not dependent on the rate of thawing of the frozen water in which the spores were suspended. 3. The logarithm of the percentage of germination appeared to be a linear function of the logarithm of the rate of subzero warming when spores were warmed at rates ranging from 0.12 to 1000 degrees C. per minute. 4. The lethal effects of slow warming from -70 to 0 degrees C. were more pronounced between about -20 and 0 degrees C. than between -70 and -20 degrees C. In the former range of temperatures, the percentage of germination decreased sharply as slow warming progressed towards 0 degrees C. 5. Slow warming from -70 to 0 degrees C. was more harmful to the spores than was a 1 or 2 hour exposure to constant temperatures between -70 and 0 degrees C. 6. Slow warming was found to be more harmful than rapid warming when spores were suspended in horse serum, 0.16 molal sodium chloride, or 0.29 molal sucrose as well as in distilled water.

Aspergillus↗
PubMed1956

The freezing point depression of mammalian tissues in relation to the question of osmotic activity of cell fluid.

The freezing point depression of freshly excised frozen tissues, pulverized in a hydraulic press or in a mortar, is greater than that of plasma. Even at 0 degrees C. the freezing point depression of such homogenates increases significantly with time. Dilution data indicate that such freezing point data are valid. The presence of intact cells has been shown in smears of tissues pulverized in a mortar, but not in smears of those crushed in a hydraulic press. The osmolarity of various diluent solutions affects the calculated osmotic activity of tissue homogenates presumably because of delayed diffusion between the diluent and cell fluid. With a hypertonic NaCl diluent, spuriously low values of tissue osmotic activity are found from calculations assuming instantaneous mixing between homogenates and diluents. The limitations of data from cryoscopic experiments and from tissue-swelling experiments are discussed in relation to the basic question of whether or not cell fluid is isotonic to extracellular fluid.

Animals↗
PubMed1958

The effect of ions upon the response of smooth muscle to cooling.

The slow tonic responses of the anterior byssus retractor of Mytilus edulis to rapid cooling were investigated by simultaneously recording tension and resting potential changes after soaking the muscle in banthine, a powerful neuromuscular blocking agent. The quantitative relations between the amount of cooling and the amount of associated depolarization necessary for contraction at various concentrations of potentiating potassium can be expressed in a family of curves. The plateaus of the curves for sea water and for potassium-free sea water were beneath the depolarization value necessary for contraction, so that it is clear that no amount of cooling with sea water alone or with potassium-free sea water would ever be effective. When the muscle is treated with subthreshold amounts of potassium and rapidly cooled in various concentrations of sodium ion and calcium ion, respectively, the sodium and calcium do not affect the amount of depolarization. Acetylcholine, in subthreshold amounts, has a potentiating effect, but, unlike potassium and cooling, acts through the nervous apparatus. Mytilus muscle will respond to cooling with tonic contraction whenever a critical threshold amount of depolarization is achieved. Cooling alone cannot trigger the contraction since it cannot bring about sufficient depolarization. Cooling can result in contraction, however, if used in conjunction with some other subthreshold depolarizing agent. Cooling affects the contractile mechanism by first causing membrane breakdown and depolarization.

Acetylcholine↗