1 10 DYNAMICS OF LIVING MATTER 



hearts is practically the same, and that a rise, of 10 C. increases the 

 rate to a little more than twice the original figures. It was found that 

 temperatures above 25 C. injure the heart rather soon, and for this 

 reason the rate of contraction was regular at a temperature of 30 C. 

 for the first fifteen or twenty minutes only. 



These experiments show that the heartbeat is caused by chemical 

 processes which go on constantly. O. Hertwig * has made experi- 

 ments on the influence of temperature upon the time required for the 

 development of the eggs of the frog. He compared the time required 

 to reach three successive stages in the development at the tempera- 

 tures of 6, 10, 15, 20, and 24. The temperatures were not kept 

 perfectly constant. From Hertwig's results E. Cohen calculated f that 

 the influence of temperature followed the law of van't Hoff and 

 Arrhenius. 



When the temperature of the protoplasm becomes sufficiently low, 

 e.g. approximately o C., the velocity of the chemical reactions becomes 

 so small that the manifestations of life cease. Cold-blooded animals 

 can at any time be revived from this condition of latent life by raising 

 their temperature. The lack of water acts similarly to a low tempera- 

 ture. This is the reason why seeds can be kept alive so long. Lack 

 of water may reduce the reaction velocity of the hydrolytic processes 

 in seeds at ordinary temperature so considerably that it may become 

 practically zero. 



The question may be raised whether lowering of the temperature 

 can ever kill an organism, or whether there exists a low temperature 

 limit for life phenomena. From our viewpoint the criterion for death 

 is the nonreversibility of the changes brought about by the agency 

 in question. We must therefore ask, Does lowering of temperature 

 bring about irreversible changes in the protoplasm, as does a raising of 

 the temperature ? The answer seems to be that for many cold-blooded 

 animals there is no lower temperature limit in the sense of our defini- 

 tion, and if death occurs at a low temperature, it is due to secondary 

 and entirely accidental effects connected with the freezing of the water 

 in the cells. It is known that the formation of ice crystals in the cells 

 may mechanically injure and kill them. This seems to be the case in 

 the freezing of plants. Another accidental irreversible change is con- 

 nected with the thawing of animals that have been frozen. It seems 

 to be certain that a frog after being frozen cannot be brought back to 

 life again if the temperature is raised suddenly, while it may live if 

 allowed to thaw slowly. Barring these two secondary and mechani- 



* O. Hertwig, Archiv fiir Mikroskop. Anatomie Tind Entwickelungsgeschichte, Vol. 51, 

 p. 319, 1898. f E. Cohen, loc. cit. 



