268 CRILE— THE KINETIC SYSTEM. [April 22, 



adolescence, and for die propagation of die species during the pro- 

 creative period. Unless other factors intervene this reduction in 

 speed is progressive until senescent death. The diminished size of 

 the thyroid of the aged bears testimony to the part the activating 

 organs bear in the general decline. 



We have now referred to variations in the rate of discharge of 

 energy in different species ; in individuals of the same species ; in 

 cycles in the same individual — such as the seasons of food supply ; 

 the periods of wakefulness and of sleep ; the procreative period — and 

 we have spoken of those variations caused artificially by thyroid 

 feeding. 



Thus far we have referred to the conversion for adaptive pur- 

 poses of latent into kinetic energy in muscular and in procreative 

 action. We shall now consider the conversion of latent into kinetic 

 energy in the production of heat/ and endeavor to answer the ques- 

 tions which arise at once: — Is there one mechanism for the conver- 

 sion of latent energy into heat and another mechanism for its con- 

 version into muscular action? What is the adaptive advantage of 

 fever in infection? 



The Purpose and the Mechanism of Heat Production in 



Infections. 

 Vaughn has shown that the presence in the body of any alien 

 protein causes an increased production of heat, and that there is no 

 difference between the production of fever by foreign protein and by 

 infections. Before the day of the hypodermic needle and of ex- 

 perimental medicine, the foreign proteins found in the body outside 

 the alimentary tract were brought in by invading microorganisms. 

 Such organisms interfered with and destroyed the host. The body, 

 therefore, was forced to evolve a means of protection against these 

 hostile organisms. The increased metabolism and fever in infection 

 might operate as a protection in two ways : the increased fever by 

 interfering with bacterial growth, and the increased metabolism by 

 breaking .up the bacteria. Bacteriologists have taught us that bac- 

 teria grow best at the normal temperature of the body, hence fever 



1 We use the terms heat and muscular action in the popular sense, 

 though physicists use them to designate one and the same kind of energy. 



