640 FUNCTIONS OF ANIMALS. 



it follows from them that there is nothing fixed or certain either 

 in the ratio between the oxygen consumed and the carbonic acid 

 formed, or in the diminution of volume of the air by breathing ; 

 or of the heat evolved. In general the more oxygen gas con- 

 sumed the greater is the quantity of heat evolved ; though this 

 does not hold rigidly in every experiment. 



That the reader may see at a glance the variations in these 

 experiments, the following table has been calculated, showing the 

 volume of oxygen consumed, and of carbonic acid formed, the di- 

 minution of the volume of air breathed, and the heat evolved, 

 supposing each animal to have breathed ten minutes : 



Oxygen con- Carbonic acid Diminutions 



sumed in cu- formed in cu- of bulk of , f d , * 



bic inches. bic inches. air. 



Man, ;'.; . ' , 119' 119* uncertain, uncertain. 



Rabbit, .- . . 25-7 19-5 ^ 7.36 



Six small rabbits, . . 20-4 14-4 fa 6 .44 



Three male guinea pigs, 17'6 13-8 T ^ F f 5.18 



A dog, five years old, 37'4 25-2 T r 12.17 



A dog, eight months old, 24-9 16-6 fa 8 .70 



Two dogs, six weeks old, 37-3 24-0 ^ 13 .33 



A male cat, . 18-9 13-2 T ^ 6.15 



Three adult male pigeons, 21 -1 16-2 ^ T 7.05 



An adult Virginian duck, 18'8 11 '5 T r 6.52 



It follows from these experiments, that the whole animal heat 

 developed in the living animal is not the consequence of the com- 

 bination of the oxygen of the atmosphere with carbon and hy- 

 drogen. If we reckon the animal heat evolved in these experi- 

 ments 100, then the portion of it due to the combination of the 

 oxygen of the atmosphere with carbon and hydrogen during the 

 circulation of the blood through the body will be 82.J Conse- 

 quently, 18, or almost one-fifth of the whole, must be owing to 

 other processes not yet sufficiently appreciated. What renders these 

 conclusions somewhat uncertain, is the great diversity in the ratios 

 of the heat evolved, and the oxygen consumed in the different ex- 



* This column indicates the number of degrees that the temperature of one 

 pound of water would be heated by the heat given out during ten minutes breathing. 



f In this case the bulk of the air was increased by breathing instead of being 

 diminished. 



\ Dr Winn has ascertained that when the elastic coat of an artery is stretch- 

 ed, heat is evolved (Phil. Mag. (3d series) xiv. 174), and he conceives that this 

 evolution will supply the surplus heat of the animal above that furnished by res- 

 piration. Not considering that when the coat contracts it must again absorb 

 all the heat evolved by the stretching, as was long ago proved to be the case 

 with caoutchouc by Mr Gough. 



