The Organism as a Whole, from a Physicochemical Viewpoint

by Jacques Loeb

It took at 100°	over sixteen hours
" "  " 105–110°	two to four hours
" "  " 115°	thirty to sixty minutes
" "  " 125–130°	five minutes or more
" "  " 135°	one to five minutes
" "  " 140°	one minute

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 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.[249] 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 Q₁₀ to become larger for lower temperature, and coefficients of Q₁₀ about 5 or 6 have repeatedly been found for purely chemical reac­tions between 0° 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 Q₁₀ with rising temperature which is also noticed in most life phenomena. Thus Van Slyke and Cullen[250] found that the reac­tion rate of the enzyme urease “is nearly doubled by every 10° rise in temperature between 10° and 50°. Within this range the temperature coefficient is nearly constant and averages 1.91. From O° to 10° it is 2.80, from 50° to 60° it is only 1.09. The optimum is at about 55°.” The rapid fall of the temperature coefficient for enzyme action at the upper temperature limit has been ascribed by Tammann to a progressive destruc­tion of the active mass of enzyme by the higher temperature (by hydrolysis). This will, however, not account for the high value of the coefficient near the lower limit. But is it not imaginable that at low temperature an aggrega­tion of the enzyme particles exists which is also equivalent to a diminu­tion of the active mass of the enzyme and that this aggrega­tion is gradually dispersed by the rising temperature? This would account for the fact that at a temperature near 0°C life phenomena stop because the enzymes are all in a state of aggrega­tion or gela­tion; that then more and more are dissolved and the rate of chemical reac­tion increases since the mass of enzyme particles increases until all the enzyme molecules are dissolved or rendered active. Under this assump­tion three processes are superposed in the varia­tion of the value of Q₁₀ with temperature: (1) the supposed increase in the number of available ferment molecules with increasing temperature near the lower temperature limit; (2) the temperature coefficient of the reac­tion velocity which is nearly = 2 for 10°C.; (3) the diminu­tion of the number of available ferment molecules by hydrolysis or some other action of the increasing temperature. This latter is noticeable near the upper temperature limit. The reason that 1 and 3 interfere more strongly in life phenomena than in the chemical reac­tions of crystalloid substances may possibly be accounted for by the fact that the enzymes and most of the constituents of living matter are colloidal, i. e., consist of particles of a considerably greater order of magnitude than the molecules of crystalloids.[251]

We will now show the rôle of the temperature coefficient upon phenomena of development. F. R. Lillie and Knowlton[252] first determined the influence of temperature upon the development of the egg of the frog and showed that it was of the same nature as that of a chemical reac­tion. These experi­ments were repeated a year later by O. Hertwig.[253]

The time required for the eggs to reach definite stages was measured for different temperatures and it was found that the temperature coefficient Q₁₀ between 2.5° and 6° was equal to 10 or more; between 6° and 15° it was between 2.6 and 4.5; between 10° and 20° it was 2.9 to 3.3, and between 20° and 24° it was between 1.4 and 2.0. To anybody who has worked on this problem it is obvious that no exact figures can be obtained in this way, since the point when a certain stage of development is reached is not so sharply defined as to exclude a certain latitude of arbitrariness. The writer found that very exact figures can be obtained on the influence of temperature upon development of the sea-urchin egg by measuring the time from insemina­tion to the first cell division. Such experi­ments were carried out in a cold-water form Strongylo­centrotus purpuratus and a form living in warmer water, Arbacia.[254] The figures on Arbacia have been verified by different observers in different years.

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