EPITHELIAL TISSUES. 95 



In order to examine isolated epithelial cells of organs, it 

 is necessary to treat the epithelial shreds or whole epithelial layers with 

 the so-called isolating or maceration fluids. These are: (i) Iodized 

 serum; (2) very dilute osmic acid (0.1% to 0.5%); (3) very weak 

 chromic acid solution (about 1:5000 of water) ; (4) 0.5% or i% solution 

 of ammonium or potassium bichromate ; and, above all, the one-third 

 alcohol recommended by Ranvier (28 vols. absolute alcohol, 72 vols. 

 distilled water). The mixture recommended by Soulier (91), consist- 

 ing of sulphocyanid of potassium or ammonium, and the mixture of 

 Ripart and Petit serve the same purpose. All these solutions are used by 

 allowing a quantity of the isolation fluid to act upon a small fresh piece 

 of epithelium for from twelve to twenty-four hours, according to the tem- 

 perature of the medium and quality of the tissue. As soon as the isola- 

 tion fluid has done its work, it is easy to complete the isolation of the 

 cells by shaking the specimen or teasing it with needles. Separation of 

 the elements may be accomplished either in the isolation solution itself or 

 in a so-called indifferent fluid, or in gum -glycerin. The macerated pre- 

 paration may be stained in a hematoxylin or carmin solution before teas- 

 ing and mounting in gum-glycerin. 



The movement of the cilia can be observed in mammalian tissues 

 by scraping the epithelium from the trachea with a scalpel and examining it 

 in an indifferent fluid. As the ciliated epithelium of mammals is very 

 delicate and sensitive, specimens with a longer duration of ciliary move- 

 ment are more desirable. They can be obtained by using the mucous 

 membrane from the palate of a frog (examine in normal salt solution). 

 Particularly large epithelial cells, as well as very long cilia, are found on 

 the gill-plates of mussels or oysters. 



In order to study the relations of mesothelial and endothe- 

 lial cells, the silver method is the most satisfactory. The outlines of the 

 mesothelial cells may be clearly brought out by placing pieces of the peri- 

 cardium, central tendon of the diaphragm, or the mesentery in a o. 75 % to 

 i /c solution of silver nitrate. Before placing in this solution, they should 

 be rinsed in distilled water in order to remove any adherent foreign bodies, 

 such as blood-corpuscles, etc. In this solution they remain until opaque, 

 which occurs in from ten to fifteen minutes. They are then again rinsed 

 with distilled water, in which they are exposed to sunlight until they 

 begin to assume a brownish -red color. Once again they are washed with 

 distilled water, and either placed in glycerin, in which they may be 

 mounted, or dehydrated and mounted in Canada balsam, according to the 

 usual methods. The margins of the cells subjected to this treatment will 

 appear black. 



Endothelial cells may be demonstrated after the following method : 

 A small mammal (rat, Guinea-pig, rabbit, or cat) is narcotized. Before 

 the heart's action is completely arrested, the thorax is opened and the 

 heart incised. As soon as the blood stops flowing, a cannula is inserted 

 and tied in the thoracic aorta a short distance above the diaphragm, and 

 50 to 80 c.c. of a i^ aqueous solution of silver nitrate injected through 

 the cannula. About fifteen minutes after the injection of the silver nitrate 

 solution, there is injected through the same cannula 100 to 150 c.c. of a 

 4 c /c solution of formalin (formalin 10 parts, distilled water 90 parts). 

 The abdominal cavity is then opened, loops of the intestine with the 

 attached mesentery removed and placed in a 4% solution of formalin, in 

 which the tissue is exposed to the sunlight. As soon as the reduction of 



