50 APPLIED PHYSIOLOGY 



highly prejudicial to a person who is intoxicated. Seeing 

 that life always manifests itself by developing heat, we 

 need not be surprised to be told that there is really no 

 such thing as a ' cold-blooded ' animal in the literal 

 sense, and that the creatures commonly so described 

 usually have a body temperature appreciably above that 

 of their surroundings. The real distinction, in fact, is 

 not between warm- and cold-blooded animals, but between 

 those whose temperature is constant and those in whom 

 it is not. 



Now, the question naturally presents itself, What are 

 the advantages of having a constant temperature, or, in 

 other words, of being what is commonly called ' warm- 

 blooded ' ? The reply to this is, that constancy of 

 temperature makes an animal more independent of its 

 surroundings. Extremes of heat and cold both tend to 

 paralyze living cells, and if the temperature of a man's 

 body fell with that of his surroundings, all his vital 

 processes would become sluggish in cold weather. On 

 the other hand, when exposed to heat, it would be 

 necessary for him to adopt a voluntary sluggishness, as 

 otherwise his temperature might rise to a point at which 

 the vitality of his cells would become impaired. In the 

 process of evolution, therefore, when animals ceased to 

 be aquatic, and came to live in a medium of varying 

 temperature, it became necessary to develop a mechanism 

 for maintaining the temperature of the body at a con- 

 stant level, and the animals which succeeded in doing 

 this in greatest perfection survived. Even yet we can 

 see in the Monotremata an example of creatures in which 

 the development of a heat-regulating mechanism has 



