94 HOMOIOTHERMISM 



Chemical force is a function of free energy. Rise in 

 temperature greatly diminishes chemical resistance. 

 Temperature, therefore, is a very important factor in 

 determining the velocity of reactions going on in a living 

 organism. The homoiotherms manifest a rapidity of 

 adjustment to external conditions which is far above that 

 shown by the poikilotherms. In addition to the effects 

 of a higher temperature on chemical reactions there is 

 also an advantage on physical processes as in the dimi- 

 nution of the internal friction of liquids such as the 

 blood, the hastening of diffusion, and the increasing of 

 the velocity of conduction of nerve impulses. The influ- 

 ence of temperature on general metabolism has already 

 been discussed. (2) A constant temperature level, which 

 assures the organism that its physiological processes 

 shall continue in a state of equilibrium, which is opti- 

 mum for the processes involved, is the second advantage. 

 A constant internal temperature thus protects the organ- 

 ism against environmental irregularity. 



It is common knowledge that in homoiotherms physi- 

 ological processes take place most readily at body tem- 

 perature. The value of a constant temperature level is 

 readily seen in the case of enzymotic activity. The en- 

 zymes are effective only through a very well defined 

 range of temperatures. Moreover, their maximum rate 

 of reaction takes place at optimum temperatures , which 

 are very near those of the bodies of homoiotherms. 

 While many chemical reactions show acceleration with 

 increased temperature, enzymes do not absolutely follow 

 this rule. They increase their activity from deg. C. to 

 about 40 deg. C, but beyond that show a gradual decrease. 

 At 60 deg. C. enzymes are destroyed. The enzymes of the 

 poikilotherms have optima like those of homoiotherms. 

 Early workers regarded the optimum as a mystery and 



