i 2 PRACTICAL HISTOLOGY. 



in a drop of salt-water, and invert it over a gas chamber so that the gill is directed towards 

 the chamber (p. xxix). 



EXAMINATION (L). Ascertain that the cilia are active, then raise the cover-glass, put a 

 small drop of chloroform into the chamber by means of a glass rod, and again apply the 

 cover-glass. The ciliary movement becomes slower and slower, and finally ceases. If, how- 

 ever, the gill is removed before the chloroform has acted too long, and is freely exposed to 

 air, the cilia may resume their movements (Lister). None of these specimens can be pre- 

 served. 



C. PERMANENT PREPARATIONS OF CILIATED EPITHELIUM. 



PREPARATION. Place a small piece of the trachea of a cat, rabbit, ox, or sheep in dilute 

 alcohol (i to 2 water) for forty-eight hours, when the inter-cellular substance of the epithelium 

 will be so softened that the cells can be easily isolated. Then wash the whole piece in water, 

 scrape the mucous membrane with a knife, place the scraping in a tube with a few drops of a 

 one per cent, solution of osmic acid. The isolated cells are thus ' fixed,' and can be examined 

 either with or without the addition of various staining reagents. 



EXAMINATION (H). Place some of the cells in picrocarmine for at least twenty-four 

 hours, transfer some to a drop of glycerine on a slide, cover and examine. Observe the 

 long, tapering character of the cells, with one end covered by a fringe of fine processes the 

 cilia which are planted on a clear disc which is not stained. The cell-protoplasm is described 

 as granular, but careful examination shows that it contains an intra-cellular plexus of fibrils 

 with the fibrils arranged chiefly in the long axis of the cell. It is maintained by some 

 observers that the cilia are actually prolonged through the clear band, so as to become 

 continuous with this plexus. The oval nucleus is placed far down in the cell, is bright red, 

 and shows a similar plexus, with a bright spot in its centre the so-called nucleolus. The 

 other end of the cell is often tapered or bifurcated (PI. II., Fig. 8). Instead of the picro- 

 carmine logwood may be used, with the advantage that a few minutes suffice for the staining 

 process. Either of these preparations may be sealed up and preserved permanently. The 

 ends of the cells may be directed towards the observer (PI. II., Fig. 9). 



4 . TRANSITIONAL EPITHELIUM. 



PREPARATION. Take the bladder of a sheep, cat, rabbit, or guinea-pig, and prepare and 

 preserve it in the same way as is directed for the preservation of ciliated epithelium. 



EXAMINATION (H). Observe the great variety in the shape of the cells, some of them 

 being more or less cubical, others resemble squames in character, while others again present a 

 number of sharp angular points (PI. II., Fig. u). 



5. SECRETORY OR GLANDULAR EPITHELIUM. 



PREPARATION. Make a cut into the liver of a dog just killed ; scrape the cut surface 

 with a knife, so as to detach some of the liver-cells. Place these in a few c.c. of a half per cent, 

 solution of osmic acid for an hour, then pour off the acid and substitute picrocarmine for 

 several hours. 



