ANIMAL HEAT 505 



to the precise relation of the energy which appears as heat 

 and of that which is converted into work. The original 

 source of both is, of course, the oxidation of the food sub- 

 stances ; but it has been the subject of discussion whether 

 in a muscle, as in a heat-engine, the chemical energy is first 

 converted into heat, and part of the heat then transformed 

 into work, or whether the chemical energy is immediately 

 changed into work, or whether there is an intermediate form 

 of energy other than heat. Some have supposed that the 

 chemical energy is first converted into electrical energy. It 

 is most probable, however, that the transformation is a direct 

 one. It has been stated that under certain conditions a 

 muscle, instead of becoming warmer, may become colder 

 during contraction. If this were established, it would be 

 in favour of the view that heat is directly transformed into 

 muscular work. But it would not be an unequivocal proof; 

 for the cooling might be due merely to chemical or physical 

 reactions between the products formed in the active muscle 

 and other muscular constituents. 



It has been very generally admitted that the chief seat of 

 excessive metabolism in fever is the muscles ; but U. Mosso 

 has stated that cocaine fever the marked rise of tempera- 

 ture produced by injection of cocaine can be obtained in 

 animals paralyzed by curara. This, even if true, would not 

 support the conclusion that a ' nervous fever ' that is to 

 say, a fever due solely to increased metabolism in the nervous 

 system exists ; for in a curarized animal a large amount of 

 ' active ' tissue (glands, heart, smooth muscle) still remains 

 in physiological connection with the brain and cord. But, 

 as a matter of fact, in an animal under a dose of curara 

 sufficient to completely paralyze the skeletal muscles cocaine 

 causes no rise of rectal temperature ; and this is strongly 

 in favour of the view that the fever produced in the non- 

 curarized animal is connected with excessive muscular 

 metabolism. 



Thermotaxis. What, now, is the mechanism by which the 

 balance is maintained in the homoiothermal animal between 

 heat-production and heat-loss ? In answering this question 

 we have to recognise that both of these quantities are 



