626 FUNCTIONS OF ANIMALS. 



is owing to some change which takes place in the blood itself, in- 

 dependent of any external agent. 



The arterial blood becomes much more rapidly and deeply 

 dark coloured when it is left in contact with hydrogen gas placed 

 above it.* We must suppose, therefore, that the presence of this 

 gas accelerates and increases the change, which would have taken 

 place upon the blood without any external agent. 



9th. If arterial blood be left in contact with oxygen gas, it 

 gradually assumes the same dark colour which it would have ac- 

 quired in vacuo, or in contact with hydrogen ; and after this 

 change oxygen can no longer restore its scarlet colour.f There- 

 fore it is only upon a part of the blood that the oxygen acts ; 

 and after this part has undergone the change which occasions 

 the dark colour, the blood loses the power of being affected by 

 oxygen. 



1 Oth. Mr Hassenfratz poured into venous blood a quantity of 

 chlorine ; the blood was instantly decomposed, and assumed a 

 deep and almost black colour. When he poured common mu- 

 riatic acid into blood, the colour was not altered.^ 



11 tli. But one of the great purposes which respiration serves is 

 the evolution of heat. The temperature of all animals depends 

 upon it. It has been long known that those animals which do 

 not breathe have a temperature but very little superior to the me- 

 dium in which they live. This is the case with fishes and many 

 insects. Man, on the contrary, and quadrupeds, which breathe, 

 have a temperature considerably higher than the atmosphere : 

 that of man is 98. Birds, which breathe in proportion a still 

 greater quantity of air than man, have a temperature equal to 

 103 or 104. 



Before attempting to give a theory of animal heat, it may be 

 worth while to state the most important facts that have been as- 

 certained respecting the temperature of man and the inferior 

 animals. 



The internal temperature of an adult man in a temperate cli- 

 mate is about 98. When he passes from a cold to a hot cli- 

 mate his temperature rises to 98^ or even to 101. In general 

 the heat under the tongue is 98, and that in the arm-pit 97 or 

 96^. But Deluc assures us that, if a thermometer be kept an 

 hour in the arm-pit, it rises to 98. There seems no difference 

 in the mean temperature of the different races of men. 



* Fourcroy, Ibid. vii. p. 149. f Ibid. ix. p. 268. \ Ibid. 



