THE TRACHEA AND LUNGS. 143 



LESSON XXVII. 



THE TRACHEA AND LUNGS. 



I. IN sections of the trachea, stained with hsematoxylin, and mounted in 

 Canada balsam, notice the ciliated epithelium, the basement-membrane (of 

 some thickness in the human trachea), the lymphoid tissue of the mucous 

 membrane, the elastic tissue external to this, and lastly the fibrous membrane 

 containing the cartilages. In the mucous membrane and submucous areolar 

 tissue look for sections of mucous glands, ducts of which may be seen opening 

 on the surface. At the back of the trachea notice the plain muscular fibres 

 transversely arranged ; there may be larger mucous glands external to these. 



2. In sections of lung similarly prepared, notice the sections of the alveoli 

 collected into groups (infundibula). Find sections of bronchial tubes, some 

 cut longitudinally and passing at their extremities into the infundibula, 

 others cut across ; the latter show the structure of the tubes best. In each 

 tube notice the ciliated epithelium internally. Next to this the mucous 

 membrane containing numerous elastic fibres and often thrown into folds ; 

 then the layer of circular muscular fibres, and, outside this, loose fibrous tissue 

 in which in larger bronchial tubes the pieces of cartilage may be seen em- 

 bedded. Small mucous glands may also be observed in the fibrous tissue 

 sending their ducts through the other layers to open on the inner surface. 

 Notice always accompanying a section of a bronchial tube the section of a 

 branch of the pulmonary artery. 



In the sections of the alveoli observe the capillary vessels passing from one 

 side to the other of the intervening septa ; and in places where the thin wall 

 of an alveolus is to be seen in the section, try and make out the network of 

 blood-capillaries upon it. Notice within the alveoli nucleated corpuscles 

 which very frequently contain dark particles in their protoplasm. They are 

 amoeboid cells which have migrated from the blood-vessels and lymphatics, 

 and have taken in inhaled particles of carbon. They seem to pass back into 

 the lung tissue, for similar cells may be seen in this. Make a sketch of part 

 of the wall of a bronchial tube and of one or two of the alveoli. 



3. In sections of lung the air-cells of which have been filled with a mixture 

 of gelatine and nitrate of silver solution the epithelium of the alveoli may be 

 studied. The sections can be made with the freezing microtome, and mounted 

 in glycerine. 



4. Mount in Canada balsam a section of lung in which the pulmonary 

 vessels have been injected. Study the general arrangement of the vessels 

 with a low power, and the network of capillaries of the alveoli with a high 

 power. Observe that the veins run apart from the arteries. Sketch the 

 capillary network of one or two adjoining alveoli. 





The trachea or windpipe is a fibrous and muscular tube, the wall of 

 which is rendered somewhat rigid by C-shaped hoops of cartilage 



