102 CHANGES EFFECTED IN THE BLOOD 'i 



cells. The external air, with which they freely con* 

 municate, accordingly rushes in through the mouth and 

 nostrils, and fills the vacuum as fast as it is made. 



Emily. But I had always supposed that the chest 

 arid lungs expanded, in consequence of the admission 

 of the air. 



Dr. J3. To be convinced that you are wrong, you 

 have only to open your mouth and nostrils as wide as 

 you please, and see if the air ever rushes in, till by a 

 voluntary effort, you begin to expand the chest. A per- 

 son would breathe equally as well, if the mouth' and 

 nostrils were closed, and an opening made in the wind- 

 pipe. When the chest contracts, the air is consequent- 

 ly expelled, and thus are produced, in constant succes- 

 sion, the two acts of inspiration and expiration. 



Emily. According to this then, these acts are alto- 

 gether involuntary, and yet you know we can delay ei- 

 ther of them a few moments, and I have heard of peo- 

 ple, whose business is to dive for pearls, who could re- 

 main underwater a half hour at a time. These facts 

 prove at least, that the function is in some measure un- 

 der the will. 



Dr. 13. These cases are, in all probability, great 

 exaggerations, though people can, no doubt, by educa- 

 tion extend the influence of the will over this function 

 to a certain extent, in the same manner as we can ac- 

 custom our constitution to a less quantity of food or ex- 

 ercise. Still the action is strictly involuntary try as 

 hard as you may, to suspend the act of inspiration, the 

 muscles will invariably contract and expand the chest, 

 in spite of your exertions. 



Emily. Supposing now the air to have penetrated 

 into the cells of the lungs I cannot imagine how it is 

 to affect the blood. In the first place, however, I should 

 more properly ask, what changes in the blood it does 

 produce. 



J> r . B. The blood conveyed to the lungs, is from 

 fi modena red converted into a bright scarlet color : itt- 



