OF THE BRAIN, ETC. 31 



only remark, that the influence of the nervous 

 system does not appear to be necessary to the 

 production of the chemical changes which the 

 blood undergoes in consequence of exposure to 

 the air in the lungs. * 



The facts now, as well as those formerly ad- 



* This conclusion is directly contrary to that deduced by 

 M. Dupuytren, from a series of experiments, made with 

 a view to ascertain the effects which follow the division 

 of the nerves of the par vagum, and it is an object of some 

 importance in the present investigation, to ascertain in what 

 manner the apparently opposite facts, observed by M. Du- 

 puytren and myself, are to be reconciled with each other. 



It was observed by this physiologist, that in an animal, in 

 which both the nerves of the par vagum are divided, the 

 blood returned from the lungs has a darker colour than na- 

 tural,, and that the animals, on whom this operation is per- 

 formed, die sooner or later with symptoms of asphyxia, not- 

 withstanding that the air continues to enter the lungs ; and 

 hence he concludes, that the changes which are produced 

 on the blood in respiration, are not the result of a mere 

 chemical process, but are dependent on the nervous influ- 

 ence, so that they cease to take place when the communi- 

 cation between the lungs and the brain is destroyed. 



M. Proven9al, in prosecuting this inquiry, ascertained that 

 the animals subjected to this experiment, give out less car- 

 bonic acid than under ordinary circumstances. 



M. Blainville observed, that the frequency of the inspira- 

 tions is much diminished ; and M. Dumas restored the scarlet 

 colour of the arterial blood by artificially inflating the lungs ; 

 and from these and other circumstances, he has arrived at 

 conclusions very different from those of M. Dupuytren. 



My own observations exactly correspond with those of 

 MM. Dumas and Blainville. After the nerves of the par 

 vagum are divided, a less quantity of carbonic acid is evolved, 

 the inspirations are much diminished in frequency, and the 

 blood in the arteries of the general system assumes a darker 



