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CHAPTER XI

THE INFLUENCE OF ENVIRONMENT

I. The term environment in relation to an organism may easily assume a mystic rôle if we assume that it can modify the organisms so that they become adapted to its peculiarities. Such ideas are difficult to comprehend from a physicochemical viewpoint, according to which environment cannot affect the living organism and non-living matter in essentially different ways. Of course we know that proteins will as a rule coagulate at temperatures far below the boiling point of water and that no life is conceivable for any length of time at temperatures above 100° C., but heat coagulation of proteins occurs as well in the test-tube as in the living organism. If we substitute for the indefinite term environment the individual physical and chemical forces which constitute environment it is possible to show that the influence of each of these forces upon the organism finds its expression in simple physicochemical laws and that there is no need to introduce any other considerations.

We select for our discussion first the most influential of external conditions, namely temperature. The reader knows that there is a lower as well as an upper temperature limit for life. Setchell has ascertained that in hot springs whose temperature is 43° C., or above, no animals or green algae are found. In hot springs whose temperature is above 43° he found only the Cyanophycea, whose structure is more closely related to that of the bacteria than to that of the algæ, inasmuch as they have neither definitely differentiated nuclei nor chromophores. The highest temperature at which Cyanophycea occurred was 63° C. Not all the Cyanophycea were able to stand temperatures above 43° C., but only a few species. The other Cyanophycea were found at a temperature below 40° C., and were no more able to stand higher temperatures than the real algæ or animals. The Cyanophyceae of the hot springs were as a rule killed by a temperature of 73°: From this we must conclude that they contain proteins whose coagulation temperature lies above that of animals. and green plants, and may be as high as 73°. Among the fungi many forms can resist a temperature above 43° or 45°; the spores can generally stand a higher temperature than the vegetative organs. Duclaux found that certain bacilli (Tyrothrix) found in cheese are killed in one minute at a temperature of from 80°

Setchell, W. A., Science, 1903, xxvii., 934.

to 90°; while for the spores of the same bacillus a temperature of from 105° to 120° was required.'

Duclaux has called attention to a fact which is of importance for the investigation of the upper temperature limit for the life of organisms. According to this author it is erroneous to speak of a definite temperature as a fatal one; instead we must speak of a deadly temperature zone. This is due to the fact that the length of time which an organism is exposed to a higher temperature is of importance. Duclaux quotes as an example a series of experiments by Christen on the spores of soil and hay bacilli. The spores were exposed to a stream of steam and the time determined which was required at the various temperatures to kill the spores.

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In warm-blooded animals 45° is generally considered a temperature at which death occurs in a few minutes; but a temperature of 44°, 43°, or 42° is also to be considered fatal with this difference only, that it takes

Duclaux, E., Traité de microbiol., 1898, i., 280.

a longer time to bring about death. This fact is to be considered in the treatment of fever.

It is generally held that death in these cases is due to an irreversible heat coagulation of proteins. According to Duclaux, it can be directly observed in micro-organisms that in the fatal temperature zone the normally homogeneous, or finely granulated, protoplasm is filled with thick, irregularly arranged bodies, and this is the optical expression of coagulation. The fact that the upper temperature limit differs so widely in different forms is explained by Duclaux through differences in the coagulation temperature of the various proteins. It is, e. g. known that the coagulation temperature varies with the amount of water of the colloid. According to Cramer, the mycelium of Penicillium contains 87.6 water to 12.4 dry matter, while the spores have 38.9 water and 61.1 dry substance. This may explain why the mycelium is killed at a lower temperature than the spores. According to Chevreul, with an increase in the amount of water, the coagulation temperature of albuminoids decreases. The reaction of the protoplasm influences the temperature of coagulation, inasmuch as it is lower when the reaction is acid, higher when the reaction is alkaline. The experiments of Pauli show also a marked influence of salts upon the temperature of coagulation of colloids.

The process of heat coagulation of colloids is also a function of time. If the exposure to high temperature

is not sufficiently long, only part of the colloid coagulates; in this case an organism may again recover.

Inside of these upper and lower temperature limits we find that life phenomena are influenced by temperature in such a way that their rate is about doubled for an increase of the temperature of 10° C., and that this temperature coefficient for 10°, Q10, very often steadily diminishes from the lower to the higher temperature; so that near the lower temperature limit it becomes often considerably greater than 2 and near the higher temperature limit it becomes very often less than 2.* This influence of temperature is so general that we are bound to associate it with an equally general feature of life phenomena; and such a feature would be most likely the chemical reactions. It is known through the work of Berthelot, van't Hoff, and Arrhenius that the temperature coefficient for the velocity of chemical reactions is also generally of about the same order of magnitude; namely 2 for a difference of 10°. In chemical reactions there is also a tendency for Q1. to become larger for lower temperature, and coefficients of Q1. about 5 or 6 have repeatedly been found for purely chemical reactions between o° and 10°, e. g., for the inversion of cane sugar by the hydrogen ion. The temperature coefficient for the reaction velocity of ferments shows the same diminution of Q.. with

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A full discussion of the literature on temperature coefficients is given in A. Kanitz's book on Temperatur und Lebensvorgänge, Berlin, 1915.

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