BY DR. KLEIN. 133 



CHAPTER IX. 

 ORGANS OF RESPIRATION. 



THE structure of the larynx, trachea, and bronchi can be 

 completely studied in sections of organs hardened in chromic 

 acid. The epithelium has been already fully described else- 

 where. An animal having just been killed, the tubes are 

 opened, washed with very dilute solution of bichromate o 

 potash, and placed in the hardening liquid. In thin sections, 

 the relations of the mucosa submucosa with its glands, carti- 

 lages, perichondHum, muscular fibres, and ganglia, may be 

 completely made out. The bloodvessels may be injected in the 

 ordinary way, and the lymphatics by puncture of the submu- 

 cosa. The network of elastic fibres which surround the alveoli 

 are most readily studied in thin sections of fresh-frozen lungs 

 of small mammalia. The sections are steeped in acidulated 

 water till the air-bubbles have escaped, and then spread out 

 on an object-glass and covered in glycerin. The structure of 

 the fine bronchi ma.y be well studied as regards its epithelium, 

 minute glands, muscular coat, and innumerable large gangli- 

 onic masses, in sections of lungs of human foetuses of the 

 last months of pregnanc}', which have been hardened in one- 

 tenth or one-eighth per cent, solution of chromic acid. The 

 flat epithelial elements of the alveoH, as well as those which 

 line the finest bronchial tubes, can be best examined in lungs 

 of small mammalia, prepared by placing a canula in the 

 trachea, removing the sternum, and then injecting the bronchi 

 with one-tenth to one-eighth percent, solution of chromic acid, 

 until the organ is moderately distended. The trachea is then 

 tied, and the lungs are carefully removed from the thorax 

 along with the heart, after separating them first from the 

 spinal column, and then from the diaphragm; the whole is 

 then placed in liquid of the same strength. Another method, 

 which, however, does not answer so well, is that of injecting 

 half per cent, solution of silver into the pulmonary artery. 

 Good injected preparations of lungs can be obtained by filling 

 the air-passages with cacao butter, and the bloodvessels with 

 gelatin-mass, simultaneously. A rabbit is killed by opening 

 the crural artery. The trachea having been prepared, a canula 

 fitted to a nozzle is fixed in it. The sternum is then removed, 

 and a second canula inserted in the pulmonary artery close to 



