on the Agenct/ of Galvanism. 75 



yuiri/ it appears, that the vessels possess no powers but the mus- 

 cular and elastic ; and that the former, as well as the latter, is 

 independent of the nervous system * ; nor is it possible to conceive 

 any modification of these powers, by which they could become 

 chemical agents, and thus be enabled to separate and recombine 

 the elementary parts of the blood. The first of the above posi- 

 tions may, therefore, be regarded as set aside ; and the necessary 

 inference seems to be, that in the function of secretion, the vessels 

 only convey the fluids to be operated upon by the nervous 

 influence. 



That the evolution of caloric is effected by the state of the 

 nervous influence, appears from many experiments. Mr. Brodie 

 has shewn that in proportion as the action of the brain is debili- 

 tated, the evolution of caloric is lessened f ; and it appears from 

 experiments which I have laid before the public, that lessening 

 the extent of the nervous system, by destroying portions of the 

 spinal marrow, has the same effect J. But it also appears from a 

 great variety of facts, that its evolution depends equally on the 

 state of the blood. It is needless to enumerate the various phe- 

 nomena of the living animal which support this position, with 

 which every Physiologist is familiar ; but it may be proper to ob- 

 serve, that I have found by many experiments §, that if the circu- 

 lation be supported by artificial respiration in the newly dead 

 animal, an evolution of caloric continues to take place, which is 

 not found to be the case when the circulation is allowed to cease. 

 Thus we see that the evolution of caloric in the animal economy 

 depends equally on the state of the nervous influence, and that of 

 the blood, and, consequently, like the formation of the secreted 

 fluids, arises from their joint operation. On this account I have 

 said, " If caloric be admitted to be a substance, its evolution 

 from the blood being effected by the same means by which the 

 secreted fluids are formed, it must be regarded as a secretion;" 



• Exper. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 31, 32, and the obser- 

 vatious iiiider Cxpcr. 32. 



■Y Croonian Lecture for lalO, and Philosnphicul Traiisacliuiis for 1813. 

 J The above Jru/uii-i/, Exper. 54, 5.T,'5t). 

 ^ The aboM- Jii'/utri/, Exper. (>4, Go, 6'(),Afc. 



