THE RESPIRA TOR Y APPARA TUS. I 77 



ably taken up from the respired air and transported 

 through the cells or lymph-channels to the parts in 

 which it is found. 



TECHNIQUE. 



Trachea. A portion of the human trachea is placed for 

 ten days in one-sixth-per-cent. solution of chromic acid, 

 and the hardening completed with alcohol. A small bit is 

 imbedded in celloidin, care being taken not to rub off the 

 ciliated cells in the manipulation, and the longitudinal 

 and transverse sections are stained double and mounted 

 in balsam. 



Uninjected Lung. The lung from the human subject, 

 or any small animal, such as the dog, rabbit or cat, hav- 

 ing been carefully removed, a canula is tied into the 

 trachea (or one of the large bronchi, if one lung only is 

 to be prepared), and the organ is distended by pouring a 

 one-sixth-per-cent. solution of chromic acid into the 

 canula, which, for this purpose, may be connected by a 

 short rubber tube with a funnel. When the lung is filled 

 and its surface tense, the trachea or bronchus is tied, and 

 the entire organ immersed in the same fluid with which 

 its alveoli are filled. After a couple of days the organ 

 may be cut in pieces and put into a stronger solution of 

 the chromic acid, one-fifth to one-fourth-per-cent. In 

 three or four days they are washed and transferred at 

 first to dilute, and then to strong alcohol. Sections may 

 be stained double and mounted in glycerin. 



To demonstrate the elastic fibres in the walls of the air- 

 vesicles, thin sections of an unstained human lung are 



