TEMPERATURE AND LIFE. 421 



a remarkable fact which neither physiologists nor chemists are able to 

 explain. 



In short, there exists among organisms a certain number of species, 

 vegetable or animal, able to withstand extremes of temperature, and 

 to live normally therein, while the majority can live only in more uni- 

 form and moderate temperatures. We will now see by what means the 

 different organisms withstand or succumb to temperatures, other than 

 those to which they naturally accomodate themselves, and to what 

 influences they are subjected. 



Let us consider first hetero thermic organisms, or cold-blooded animals, 

 which follow the oscillations of the surrounding atmosphere, and the 

 temperature of which rises and falls proportionately on account of the 

 absence of the regulating apparatus by which they could control their 

 own jjroductiou and loss of heat. These organisms possess a sensibility 

 which is regardless of variations in their temperature. They can un- 

 dergo with impunity oscillations in the atmosphere about them which 

 would endanger the life of warm-blooded animals, possibly destroying 

 it entirely. The latter, man included, can not live a moment if their in- 

 ternal temperature exceeds about 45° (113° F.) Thecoldblooded animals 

 can vary their temperature within very considerable limits. The enu- 

 meration of the latter would not be particularly interesting; it is sufiB- 

 cient to say that the temperature of cold-blooded animals of our coun- 

 tries varies according to circumstances from 0° to 35° and 40°. That 

 which arrests our attention is the summing up of the influence of ditfer- 

 ent temperatures on the functions of these animals. As a matter of 

 course, temperatures exist which are not deadly, which are consistent 

 with the life of these creatures. We shall see later in what way the ex- 

 tremes of temperature act. 



It is a well-substantiated fact, by means of experiments which, though 

 not numerous, are very exact, that there is for every living creature a 

 degree of heat which is absolutely indispensable in order that its devel- 

 opment be as complete as possible. On this point we have had for 

 several years, thanks to the valuable labors of Boussingault, most inter- 

 esting data. Being given a certain vegetable we can estimate that the 

 time which elapses between the appearance of its vegetation and its 

 complete maturity is short in proportion to the height of the tempera- 

 ture at which it vegetates, and long in proportion to its degree of low- 

 hess, exception being made, let it be understood, of thermic conditions 

 which are dangerous or fatal. Otherwise stated : Being given a plant 

 which lives between 15° and 30°, of which the thermic optiinum is 25°, 

 its development will be slower in a constant temperature of 15° than in 

 one of 20° to 25°, and the retardation is proportionate to the thermic 

 difference. It seems that in whatever latitude or climate it thrives, 

 there exists there for the plant just the quantity of heat necessary for 

 its development. It is easy to prove that this hypothesis is exact and 

 conforms to the facts of the case. The following is an example : From 



