234 Medicine, 



first hints towards art explanation of the cause of 

 temperature in breathing animals. It was ob- 

 served, in a preceding chapter, that the discoveries 

 of this eminent chemist place him in a high rank, 

 and constitute much of the foundation of that che- 

 mical philosophy which is the boast of rr^oderri 

 times, and the source of numberless improvements 

 in the arts and sciences. He early perceived the 

 light which his doctrine of latent heat v/as calculat- 

 ed to shed on the temperature of animals, and with 

 great sagacity availed himself of the advantage. 



Dr. Black formed the following theory of ani- 

 mal heat. He supposed part of the latent heat of 

 the air received into the lungs to become sensible; 

 that the temperature of that organ and of the blood 

 passing through it is consequently raised; and 

 that the blood, thus heated, communicates its 

 temperature to the whole body. This opinion wa^ 

 plausible, but by no means free from objections;, 

 for admitting the truth of it, the heat of the body 

 ought to be highest in the lungs, and thence gra- 

 dually to abate in proceeding to the extremities; 

 which is not the fact. The author's attempts to 

 support this theory were so feeble as to induce the 

 belief that he himself considered it as untenable. 



Lavoisier first announced, in 1777, that animal 

 heat was owing to the caloric disengaged from 

 oxygen gas, during its decomposition and conden- 

 sation in the lungs. Dr. Crawford, in 1779, 

 adopted this opinion,, and supported it by experi- 

 ments. They both believed that all the changes 

 produced by respiration are performed in the lungs;, 

 and their theory differs but little in reality from 

 that of Dr. Black, They supposed the oxygen 

 gas of the atmosphere to combine in the lungs 

 with the hydrogen and carbon emitted by the 

 blood; that, during this combination, the oxygen 

 gas sets free a great quantity of caloric; and that 



