716 



SUMMAKY OF CURRENT KESEARCHES RELATING TO 



pulmonary sacs can then be distended at pleasure and the dis- 

 tension maintained by closing the tap. To prevent the air returning 



Fig. 141. 



through the lips of the glottis, that end of the tube (fig. 142) is 

 provided with a membranous bag m (formed of a piece of frog's 



Fig. 142. 



intestine tied round the end communicating with the tube c by three 

 holes t When the tube is filled with air this bag dilates and 



Fig. 144. 



closes the mouth of the glottis against any return of the air from the 

 lung. 



