

HISTOLOGICAL DEMONSTRATIONS. 73 



laid open, washed in distilled water, and silvered ( 328), the out- 

 lines of the cells are rendered dark and distinct. In the silver process 

 in this case, use -| per cent solution of silver nitrate, and agitate the in- 

 testine in the solution for a minute or so. 



97. The existence of mucin in the ordinary columnar cells may be 

 thus shown. Scrape the mucous membrane of the frog's small in- 

 testine. Diffuse the scraping with a needle in a drop of water. Cover, 

 and examine at once. From the striated ends of the cells very deli- 

 cate hyaline blebs rapidly grow and become detached, their place being 

 taken by others. These hyaline corpuscles apparently result from 

 endosmose into the mucin within the cells. 



The precise significance of chalice cells must still be 

 regarded as doubtful. Whether they are to be regarded as 

 unicellular glands (F. E. Schultze) for the special purpose 

 of secreting mucus, or whether they are merely old cells 

 undergoing mucin transformation and breaking down, is not 

 fully shown. The fact that cells resembling them may be 

 produced in large numbers by prolonged maceration of the 

 intestine in chromic acid favours the latter view. 



98. Transitional Epithelium (H.) Examine a pre- 

 paration made by scraping the mucous membrane of the 

 bladder of cat or rabbit prepared as directed in ( 8), and 

 preserved in Farrants' solution. In this variety of epithe- 

 lium the cells may be squamous, columnar, or quite indefi- 

 nite in shape. 



The various forms of secreting epithelium will be exa- 

 mined in the different glands, and other points regarding 

 epithelium will be conveniently studied with the various 

 organs. 



CONNECTIVE TISSUES. 



99. Elastic Tissue (H.) Cut the ligamentum nucha 

 of a calf or ox vertically, and strip off a few fibres from the 

 cut surface with forceps. Place the tissue on a slide, add 

 a drop of acetic acid, and tease it thoroughly with a pair of 

 needles ( 290, a). The acetic acid softens the white 

 fibrous tissue of the ligament, and so facilitates the separa- 

 tion of the elastic fibres, upon which it appears to have 

 no action. Cover, and examine. 



