TEMPERATURE AND LIFE. 415 



cation. Chemistry shows us by exact analyses that different bodies, in 

 oxidation, evolve varyiug degrees of heat. Let us imagine a given 

 quantity of oxygen introduced into the blood to assist the oxidations 

 which are the principal though not exclusive source of animal heat. 

 The amount of heat which will be produced by the combustion of this 

 volume of oxygen with the material existing in the tissues will vary ac- 

 cording to the nature of the material. Combining with certain sub- 

 stances the same quantity of oxygen will generate ten times more heat 

 than will result from certain other combinations. That which is true 

 of oxidations is also true of other chemical phenomena incident to ca- 

 lorification — that is to say, hydrations, de-hydrations, decompositions, 

 combinations, etc. The production of heat varies considerabl}' accord- 

 ing to the chemical nature of the substances which are influenced by 

 these modifications. It is enough to say that certain foods are more 

 ])roductive of heat than others. Observation has long since shown the 

 effects, in a cold climate, of a diet rich in fats and in sugar, and expe- 

 rience establishes the fact that these substances develop a greater de- 

 gree of heat than albuminoids. On the other hand, we all know that 

 inhabitants of warm climates need less food and are more abstemious 

 than those of a cold region. The need for being heated is less pro- 

 nounced in their case on account of the temperature in which they live, 

 and in which the external cooling is little or nothing in extent. 



The relations which exist between the processes of calorification and 

 respiration are no less evident. Anything that obstructs respiration 

 obstructs also the generation of heat. This is more pronounced in the 

 case of creatures with whom oxidation plays a very important part in 

 the generation of heat. The deprivation or diminution of pure air very 

 quickly results in serious disturbance, due to the irregularity occa- 

 sioned in the vital functions by an insutiicient exchange between the 

 blood and the atmosphere. Supposing that life were possible during 

 a temporary but somewhat prolonged cessation of respiration, the 

 temperature of the body would quickly diminish. The higher class 

 of beings may not furnish proof of this fact, being so exceedingly sensi- 

 tive to the deprivation of pure air, but by the lower organisms it is 

 clearly proven. We have seen it in depriving of its share of oxygen 

 a flower of arum or of colocasia by dipping it cither in oil or in azote, 

 when the phenomenon of thermogenesis is considerably diminished. 



In fine, the relations of calorification to the activity of the organism 

 are quite as clear as those of which we have just spoken. These are 

 manifest among vegetables as among animals. With the first the 

 generation of heat is greatest during movement, or in reference to the 

 more active i)ortions, from the point of view of vitality and growth, 

 and during the organization of the tissues; in germs, in which the 

 chemical changes are rapid, numerous, intense, and in flowers during 

 the operation of fecundation. 



With animals all activity is accompanied by an elevation of the tem- 



