322 ORGANS OF RESPIRATION. 



TECHNIC. 



For the demonstration of the larynx and trachea, young and 

 healthy subjects should be selected. Pieces of the mucous membrane or 

 the whole organ should be immersed in a fresh condition. Sections 

 through the entire organ present only a general structural view ; but if 

 a close examination of accurately fixed mucous membrane be desired, the 

 latter should be removed with a razor before sectioning and treated 

 separately. 



Chromic-osmic acid mixtures are recommended as fixing agents, 

 and safranin as a stain. Besides the nuclear differentiation, the goblet cells 

 stain brown, and the elastic network of the stratum proprium and the 

 submucosa a reddish -brown. 



For examining the epithelium, isolation methods are employed, such 

 as the y$ alcohol of Ranvier. 



The examination of the respiratory epithelium is attended with 

 peculiar difficulty ; it is, perhaps, best accomplished by injecting a 

 0.5% solution of silver nitrate into the bronchus until the lumen is 

 completely filled, and then placing the whole in a 0.5% solution of the 

 same salt. After a few hours, wash with distilled water and transfer to 

 70% alcohol. Thick sections are now cut and portions of the respiratory 

 passages examined ; the silver lines represent the margins of the epithe- 

 lial cells. Such sections should not be fastened to the slide with albumen, 

 as the latter soon darkens and blurs the picture. These specimens may 

 also be stained. 



For the elastic fibers, especially those of the alveoli, fixation In 

 Miiller's fluid or in alcohol and staining with orcein is a good 

 method, as also Weigert's differential elastic tissue stain. Fresh pieces 

 of lung tissue treated with potassium hydrate show numerous isolated elastic 

 fibers. 



Pulmonary tissue may be treated by Golgi's method, which 

 brings out a reticular connective-tissue structure in the vessels and alveoli. 



The pulmonary vessels may be injected with comparative ease. 



The thyroid gland is best fixed in Flemming's solution ; it is 

 then stained with M. Heidenhain's hematoxylin solution or, better still, 

 with the Ehrlich-Biondi mixture which differentiates the chief from the 

 colloid cells ; the former do not stain at all, while the latter appear red 

 with a green nucleus (Langendorff). The colloid substance of the thy- 

 roid gland does not cloud in alcohol or chromic acid, nor does it coagu- 

 late in acetic acid, but swells in the latter; 33% potassium hydrate 

 hardly causes the colloid material to swell at all, though in weaker solu- 

 tions it dissolves after a long time. 



