TRACHEA. 55 



transverse section, with this difference, that the mucous glands are seen to be most numerous 

 between the cartilages, and the longitudinally disposed elastic fibres under the epithelium 

 can now be detected. Study these various parts under a high power. 



HUMAN TRACHEA. 



Transverse section of a Human Trachea, stained with picrocarmine and mounted in Farrant's 

 solution. 



EXAMINATION (L). Observe the same general arrangement of cartilage, glands, tracheal 

 muscle, and mucous coat as described in the cat's trachea. Notice, however, that the ciliated 

 epithelium is usually absent at some parts, from the difficulty of getting perfectly fresh tis- 

 sue to preserve. An important point is the existence of a well-marked layer of tissue 

 stained of a deep red a ' basement membrane ' so called. It lies immediately under the 

 epithelium inside the longitudinally disposed layer of elastic tissue. It is a marked feature in 

 the human trachea, and plays an important part in pathological changes, especially in those 

 resulting from chronic bronchitis. Observe the mucous glands and their ducts ; the acini of 

 many of them -lie outside the trachealis muscles, so that their ducts have to perforate it to 

 reach the surface of the trachea. The largest glands lie posteriorly, and they present the 

 same characters as previously described, their appearance varying with their state of physio- 

 logical activity. 



(H). Where the superficial epithelium has been detached, good examples of developing 

 epithelial cells may be studied. Study each of the other structures in detail. 



The so-called 'basement membrane,' it seems to me, resembles very closely a similar struc- 

 ture which exists in the mucous coat of the cat's stomach, though there its relation to the gland- 

 structures is different. I am unable to discover any corresponding structure in the trachea of 

 the rabbit, cat, or dog. Its structure, relations, and homologies require further investigation. 

 It is certainly quite different from the basement-membrane made up of epithelial cells, and 

 described by Debove as occurring under the epithelium of an intestinal villus, the bladder, 

 trachea, &c. 



Double-stain a section of human trachea with picrocarmine and iodine green. 



TRANSVERSE SECTION OF A BRONCHUS AT THE ROOT OF THE LUNG. 



Place a section in a quarter per cent, solution of osmic acid for twenty-four hours, and 

 mount it in Farrant's solution, and another ought to be stained with picrocarmine and simi- 

 larly mounted. 



EXAMINATION (L). Observe the bronchus, and note on each side of it a large blood- 

 vessel, the one a branch of the pulmonary artery, and the other, on the opposite side, a branch 

 of the pulmonary vein. These three structures lie in channels, and are imbedded in connec- 

 tive tissue, and are thus accurately mapped off from the adjacent vesicular lung-tissue. 



Observe the bronchus. Note that several pieces of hyaline cartilage are inserted in the 

 bronchial wall. Outside them is connective tissue often containing a few fat-cells which are 

 blackened in the osmic acid preparation. Besides this, note transverse sections of small 

 blood-vessels the bronchial arteries, and, lying near them, transverse sections of nerves, with 

 perhaps a ganglion in their course. Observe the mucous coat thrown into folds, and under it 

 the cut ends of longitudinally disposed elastic fibres. Outside this a continuous ring of non- 

 striped muscular fibre the bronchial muscle. It is perforated here and there by the ducts of 



