on the Generation of Animal Heat. 413 



The facts now, as wtll as those formerly adduced, go far 

 towardb provintr, thai the temperature of wartn-blooded 

 animals is coii>iderahIy under the influence of the nervous 

 system : but what is the iiatuie of the connection between 

 them ? whelher is the i)rain directlv or indirectly necessary 

 to the production of heat ? tiiese are questions to which 

 no answers can be given, except such as are purely hvpo- 

 thetical. At present ue must be content wiih (he know- 

 ledge of the insulated fact: future observations mav, per- 

 hap-:, enable us to refer it to some n)ore general principle. 



We have evidence, that when the brain ceases to exer- 

 cise its functions, although those of the heart and knurs 

 continue to be performed, the animal loses the power of 

 generating heat. , it would, however, be absurd to arous 

 from this fact, that the chemical changes of the bloofTin 

 the lungs are in no way necessary to the prnduction of 

 heat, since we know of no instance in which it continues 

 to take place alter respiration has ceased. 



It must be owned, that this part of pliysiology still pre- 

 sents an ample field for investieation. 



Of opinions sanctioned by the names of Bluck, Laplace, 

 Lavoisier, and Cravvtord, it is proper to speak with eauiion 

 and respect i but without trespassing on these ftelini'S, f 



vh.1t manner the apparently opposite facts, observed by M. Dupuytren and 

 myself, are to be reconciled wiih each o'.her. 



It nas observed by this physiolojrist, ihat in an animal, in which both the 

 nerves of the par vaguni are iiivid(d, ihe blood letiirned from the lunp-s has 

 a darker colour than uatuial, ai.d ihat the anii-.i.Js. on whoin this operation 

 is performed, die sooner or later vr^iih syniptouis of asphvxia, notwiih- 

 stauding the air continues to enter the lungs ; and hence he coiiciudes, that 

 the changes which an- produced on the biijod in respii-ation are iiot the re- 

 sult of a mere chemical pri.cess, but are dependent on the nervous influence, 

 and cease to take place when the communicaiion between ihe lungs and 

 the brain is destroyed. 



M. I'rovengal, in prosecuting this inquiry, ascertained that the animals 

 •ul>jectcd to this experiment give out less carb(inic acid than before 



M. Blainville observed ihat the frequencv of the inspiraiions i~ much 

 diminished; and M. Dun. as restored the scarlet colour ol ilie arteri.il Mood 

 by artificially inflating the lungs, and from these and oilier circumstances 

 be has arrived at conclusions very (ailll'renl from those of M. Dupuvcren. 



My own observations exactly correspond witli those of MM.Duuia* and 

 Blainviile. After the ner\ej of the par vagum are divided, a less quantity 

 of carbonic acid is evolv<d, the inspirations are much oiminished in fre- 

 quencv, and the blood in the arteries of the general syMeiu assumes a darker 

 liue; but its natural colour may be restored bv artilicially inflating the 

 lungs, so as to furnish a greater supply of air' to the blood circufating 

 through iheni. 



We may ^uppose tliat, on the division of these nerves, the sensibility of 

 the liingi. is either extremely impaired, or altogether destroyed, ,so that the 

 animal dixs not leel the same desire to draw in fresh air: in coni,e(|ueiice 

 hia inspiiations become less Ireiiutnt than natural, and iience arise the phx- 

 Bomena produced by tliii operation. 



niay 



