4 1 4- On the Influence of the Brain 



may be allowed to say, that it does not appear to mc that 

 any of the theories hitherto proposed afford a vety satisfac- 

 tory explanation of the source of animal heat. 



Where so many and such various chemical processes are 

 going on, as in the living body, are we justified in selecting 

 anv one of these for the purpose of explaining the pro- 

 duction of heat ? 



To the origmal theory of Dr. Black there is this unan- 

 • vverable objection, that the temptrature of the lungs is n(it 

 greater than that of ifie re^t of the system. To this ob- 

 jection the ingenious and beautiful theory of Dr. Craw- 

 ibrd is not opm; but still it is founded on the same basis 

 with that of Dr. Black," the conversion of oxygen into 

 carbonic acid in the lungs ;" and hence it appears to be 

 difficult to reconcile either of them with the results of the 

 experiments which have been related. 



It may perhaps be urged, that as in these experiments 

 the secretions had nearly if not entirely ceased^ it is pro- 

 bable that the other changes which take place in the ca- 

 pillary vessels had ceased also ; and that, altliough the 

 action of the air on the blood mieht have been the same 

 as under ordinary circumstances, there might not have 

 been the same alteration in the specific heat of this fluid, 

 as it flowed from the arteries into the veins. But on this 

 supposition, if the theory of Dr. Crawford be admitted as 

 correct, there must have been a gradual but enormous ac- 

 cumulation of latent heat in the blood, which we cannot 

 suppose to have taken place without its nature having been 

 eniirely altered. If the blood undergoes the usual change 

 in the capillary system of the pulmonary, it is probabU 

 that it nnist undeigo the usual change in the capillary sy- 

 8ten) of the greater circ'.laiion also, since these changes are 

 obviously dependent on and connected with each other. 

 The blood in the aorta and pulmonary veins was not more 

 florid, and that in the vena cava and pulmonary artery was 

 not les3 dark-coloured, than under ordinary circiunstances. 

 V/e may moreov er remark, that the most copiou? secretions 

 in the whole body are those of the insensiblt- perspiration 

 from the skin, and of the watery vapour from the mouth and 

 iauces, and the efteet of these nujst be to iovver rather than 

 to raise the ammal temperature. Under other circum- 

 stances also the diminution of the secretions is not observed 

 to be attended with a dnrnnution of heat. On the con- 

 trary, in the hot fit of a fever, when the scanty dark-co- 

 loured urine, dry skin and parciied mouth indicate that 

 scarcely any secretions are taking place, ilij temperature of 



the 



