GALEN". 59 



mouth, and that it is in this way that infants extract the 

 milk from the mother's breast. 



Again, Erasistratus supposed that the vapour of char- 

 coal and of certain pits and wells was fatal to life because 

 lighter than common air, but Galen maintained it to be 

 heavier. 



He describes two kinds of respiration, one by the 

 mouths of the arteries of the lungs, and one by the 

 mouths of the arteries of the skin. In each case, he 

 says, the surrounding air is drawn into the vessels during 

 their diastole, for the purpose of cooling the blood, and 

 during their systole the fuliginous particles derived from 

 the blood and other fluids of the body are forced out. 



He considers the diaphragm to be the principal muscle 

 of respiration, but he makes a clear distinction between 

 ordinary respiration, which he calls a natural and involun- 

 tary effort, and that deliberate and forced respiration 

 which is obedient to the will ; and he says that there are 

 different muscles for the two purposes. Elsewhere he 

 particularly points out the two sets of intercostal muscles 

 and their mode of action, of which, before his time, he 

 asserts that anatomists were ignorant. 



He describes various effects produced on respiration 

 and on the voice by the division of those nerves which 

 are connected with the thorax; and shows particularly 

 the effect of dividing the recurrent branch of his sixth 

 pair of cerebral nerves (the pneumogastric of modern 



