LUNGS. 57 



fibres, and carefully distinguish the plexus of capillaries, sometimes containing a few blood-cor- 

 puscles. (Indicate the epithelium and elastic fibres in PI. XL, Fig 3.) In the capillary wall 

 observe the nuclei, which are not to be confounded with those of the squames lining the 

 air-vesicle. In the cat's lung, fusiform nuclei, indicating the existence of non-striped muscle 

 between the vesicles, are to be detected. The amount of non-striped muscle between the air- 

 vesicles is sometimes greatly increased in amount in certain diseases. It is easy to see this 

 in the lungs of a cat suffering from the presence of the ova of a worm (Ollulanus triaispis) in 

 the lungs (Stirling). Select a very small bronchus cut longitudinally. Both cartilage and 

 glands have disappeared from its walls, and the epithelium lining it is not so tall as in larger 

 bronchi. Trace it into an alveolar duct, which passes into the infundibulum, into which the 

 terminal alveoli open on all sides. In the alveolar duct and infundibulum the epithelium con- 

 sists of low polyhedral cells without cilia. The walls of the alveolar ducts and infundibula 

 contain many non-striped muscular fibres, disposed circularly, which are in direct continuity 

 with the bronchial muscle. 



Picrocarmine Preparation. Stain a similar section with picrocarmine, and mount it in 

 Farrant's solution. After several days it shows the above details, even better than the dammar 

 preparation. 



Osmic Acid Preparation. Place a section of lung, hardened, as above, in chromic acid and 

 spirit mixture, in a quarter per cent, solution of osmic acid for twenty-four hours, and, after 

 washing, mount it in Farrant's solution. It shows the above details most beautifully ; the 

 elastic fibres stand out very prominently, and their arrangement is easily made out. 



Vertical Section of Human Pleura and Lung. Prepared as above, and similarly mounted. 

 Note the more conspicuous interlobular septa, often pigmented from the deposition of charcoal 

 particles in the lymphatics. Compare other parts of the section, and note especially the 

 branching character of the elastic tissue, for the physician is sometimes called on to recognise 

 these fibres in the sputum of a person suffering from gangrene of the lur^f^- 



UKIVEKSITY^ 



HUMAN FCETAL LUNG. 



Prepare the lung of a foetus preferably one that has not respired in the" same way", with 

 chromic acid and spirit mixture, as directed for adult lung. In ten days it will be ready 

 for cutting. Or, use picric acid solution as the injecting and hardening medium, which will 

 harden it in two days. Make sections across a lung, and, after staining with picrocarmine, 

 mount in Farrant's solution. 



EXAMINATION (L). Observe the distinct lung-lobules, each covered on its free broad end 

 by a relatively thick pleura, and separated from its neighbouring lobule by thick interlobular 

 septa, whose continuity with the adventitia or connective tissue of the intra-pulmonary bronchus 

 can easily be made out. In each interlobular septum note the large open spaces, which are 

 sections of the interlobular lymphatics. Study the small non-distended air-vesicles, and note 

 (H) that they are lined by low cubical cells, not yet converted into squames by the distension 

 of the lung as the result of the act of inspiration. (Indicate the pleura and interlobular septa 

 in PI. XI., Fig. 6.) 



SQUAMOUS EPITHELIUM OF THE AIR-VESICLES. 



PREPARATION. Remove the lungs of a cat or kitten from the thorax, and distend them 

 with a quarter per cent, solution of nitrate of silver, and keep them distended by tying a 

 stri ng round the trachea. Place them, with a weight attached, in alcohol until required. When 



I 



