44 EPITHELIUM AND ENDOTHELIUM. 



that of coloring by means of a solution of nitrate of silver. 

 This method consists in bathing the fresh membrane, which, 

 of course, has not been allowed to come into contact with 

 blood or any injurious fluid, in a quarter or half per cent, so- 

 lution of nitrate of silver. After immersion in this for a few 

 minutes, it is washed out in ordinary water, which must be 

 renewed as often as it becomes turbid, and is then exposed to 

 tha light until it assumes a brownish color. The portion of 

 membrane thus treated is spread out upon a glass, slide and 

 covered, a small drop of glycerine having been previously 

 placed on the under surface of the cover-glass. On superficial 

 examination a system of dnrlf linnn.Ia secu, -wlirdfbcnmrt clear 

 spaces of various forms and sizes corresponding to the indi- 

 vidual endothelial cells. Before mounting such a portion of 

 membrane in glycerine, after having colored it with silver, we 

 may place it for a short time in very dilute ammoniacal car- 

 mine solution (to which, however, two small drops of acetic 

 acid have been previously added), and then wash it in slightly 

 acidulated water. We shall then find, on mounting the speci- 

 men, that nuclei .appear in the spaces above mentioned: these 

 are sometimes central, but more often to one side, and are ob- 

 long in form. According to the duration of the action of the 

 carmine solution, and to its strength, they are more or less 

 intensely colored. Ity a modification of the silver method we 

 may demonstrate, not only the nuclei and dark lines, but also 

 the cell substance of the endothelin. This method always 

 succeeds with the endothelium which lines the lymph sacs of 

 the frog, and with that of the abdominal side of the diaphragm: 

 sometimes also with the endothelium of other serous mem- 

 branes. If we allow the membranes mentioned to lie for a 

 longer time (ten to fifteen minutes) in a half per cent, nitrate 

 of silver solution, and then simply wash them in water, and 

 mount them in glycerine after they have acquired a brown 

 color, we shall be able to recognize, after an interval of from 

 twelve to twenty-four hours, or often even earlier, the sub- 

 stance of the endothelial cells as a yellow or dark brown pre- 

 cipitation surrounding the clear oval nucleus. In preparing 

 specimens with silver it is in general much to be recommended 

 to mount the objects in glycerine, as soon as they have assumed 

 a brownish tint, and not to leave them exposed to the light for 

 an unnecessarily long time, otherwise they are apt to lose their 

 beauty and clearness, from the occurrence of dark precipitates. 

 In many parts of silver-colored serous membranes a peculiar 

 arrangement of the endothelium is observed, which consists in 

 the existence of dark or clear spaces of various forms, around 

 which the cells are set in a radiating manner. Each of these 

 small apertures occurs at the point of junction of three or 

 more endothelial cells, the interstitial lines of which radiate 



