XXVII.] 



THE RESPIRATORY ORGANS. 



29$ 



THE RESPIRATORY ORGANS. 



Methods. (i.) Place small portions of the trachea of a cut and the 

 human trachea in .2 per cent, chromic acid (10-14 days) or sub- 

 limate, and harden afterwards in gradually increasing strengths of 

 alcohol. 



(ii.) Fill the lungs of a cat with .2 per cent, chromic acid, and 

 after closing the trachea suspend them in a large quantity of the 

 same fluid. After two days cut them into small portions and keep 

 them (14-20 days) in fresh chromic acid solution and complete the 

 hardening in alcohol. 



(iii.) Harden small parts of the human lung as fresh as possible 

 in the same fluids. 



(iv.) Fix: the trachea in Flemming's fluid, harden in alcohol, and 

 stain with safranin. Admirable for epithelium. 



Trachea. Make transverse sections across the trachea of a cat, 

 and also longitudinal vertical sections, so as to include the cartilage 

 of two or three rings. This 

 is best done by staining in 

 bulk and cutting in paraffin. 

 If done by freezing, stain 

 T.S. and L.S. sections in 

 hsematoxylin, and mount in 

 balsam ; others in picro-car- 

 mine, and mount in Farrant's 

 solution. 



1. T.S. Trachea (fig. 283). 



(a.) (L) Observe internally 

 the mucous coat, outside it 

 the submucous coat, and 

 external to this an incom- 

 plete ring of hyaline cartilage 

 embedded in the outer or 

 fibrous coat. The fibrous coat becomes continuous with the sub- 

 mucous coat. 



(h.) (H) The fibrous coat of connective tissue, and embedded 

 in it an incomplete ring of hyaline cartilage. Notice the arrange- 

 ment of the cartilage cells in the latter. The ring is deficient 

 posteriorly, but bridging ovef the gap and extending between the 

 ends of the cartilage there is a transverse band of smooth muscle, 

 the frachealis muscle. Outside it are muscular fibres cut trans- 

 versely. The coats just inside the muscle are apt to be thrown 

 into folds in a trachea detached from all its surroundings. Sections 

 of nerves perhaps with ganglionic cells may be seen near the 

 muscle. 



83 __ TA ^^ ot KiUen> x 15 . 



