RESPIRATION. 631 



Fourth series of experiments. 



Poodle dog. Thorax, . . 101. 93 



Muscle of thigh, . 100.8o Brain, . . 101 -93 



Becquerel found that when the muscles were made to contract, 

 their temperature was increased about 0.9. If while the wire 

 is in the biceps muscle of the arm, the individual experimented 

 on saws a piece of wood for about five minutes with that arm, 

 the temperature increases about 1.8. Agitation, motion, and in 

 general every thing which occasions an afflux of blood has a 

 tendency to raise the temperature of a muscle. When an ar- 

 tery going to a muscle is compressed so as to diminish the flow 

 of blood to it, the temperature of the muscle sinks. 



12. Ever since the publication of Mayow's tracts, or at least 

 ever since the speculations of Dr Black on heat, became known 

 to chemists, it has been the general opinion of physiologists that 

 animal heat is generated by respiration. And in the year 1777, the 

 theory of Dr Black, respecting latent and specific heat, was ap- 

 plied to the explanation of respiration by Dr Adair Crawford. 

 The experiments on the specific heat of the gases, upon which 

 Dr Crawford's Theory of Animal Heat is founded, were repeat- 

 ed by him again in London, with greater care and with a better 

 apparatus, and the errors into which he had fallen, (which, how- 

 ever, did not affect his theory,) were corrected in the second edi- 

 tion of his work, published in 1788. 



Dr Crawford's theory of animal heat was generally adopted 

 by physiologists till the publication in 1812 of Sir Benjamin 

 Brodie's very curious and important experiments on the influ- 

 ence of the brain in the production of animal heat.* These ex- 

 periments show that the action of the brain or the nervous energy 

 has considerable influence on the production of animal heat. He 

 considered it as proved, that the volume of air was not altered 

 by respiration, and that no other change took place in it except 

 the substitution of carbonic acid gas for an equal volume of oxy- 

 gen gas which had disappeared. His experiments were made upon 

 rabbits. 



(1.) A rabbit whose volume was 50 cubic inches in thirty mi- 

 nutes converted 25'3 cubic inches of oxygen gas into carbonic 

 acid. 



(2.) A rabbit of the volume 48 cubic inches in thirty minutes 

 converted 28 -22 cubic inches of oxygen into carbonic acid. 



* Phil, Trans. 1812, p. 378. 



