BY DR. KLEIN. 119 



large size, they are prepared as follows : A portion of the 

 vessel taken from the freshly killed animal is washed with di- 

 luted serum and then dipped for a few minutes in half per 

 cent, solution of silver. Its internal surface is then exposed 

 to light until it acquires a brownish-yellow color. If the mus- 

 cular wall is thick, the intima must be separated by the meth- 

 od previously described (Chapter III. p. 48) and covered in 

 glycerin, with its endothelial surface upwards. If the vessel 

 is thin-walled, e. g., the vena cava of a small animal, it can be 

 covered without any preparation. For the endothelium of 

 capillaries in the kidney or bladder, or in the serous mem- 

 branes, the best results are obtained by injection of the solu- 

 tion of nitrate of silver. In the serous membranes, however, 

 e. g., in the mesentery, good preparations can be obtained by 

 first pencilling one or both surfaces with fresh serum in situ 

 (fche animal having been bled to death) and then cutting out 

 the pencilled part and coloring in silver in the usual way 



The endothelium of the large arteries consists of long nar- 

 row spindle-shaped \ lates. The nucleus is oblong', and usual- 

 ly in the middle of each plate. The interstitial lines are very 

 slightly sinuous. The endothelial elements of the veins are 

 relatively broader. If the staining is intense, the cell is filled 

 with brown precipitate, the nucleus remaining clear. The ca- 

 pillary vessels appear, when colored with silver, to consist 

 merely of oblong plates, the interstitial lines of which are com- 

 monly more or less sinuous. The oblong regular nuclei of the 

 walls of the capillaries seen in profile are those of the endo- 

 thelium elements. It is easy to color the nuclei by carmine, 

 in which case an acid solution must be used, i. e., an ammoni- 

 acal solution to which a sufficient quantity of acetic acid has 

 been added to render it distinctly acid. Larger vessels must 

 be immersed in the solution, but for capillaries it is enough to 

 immerse the membrane in which they are contained. Ten 

 minutes' immersion is sufficient for the purpose: the prepara- 

 tion must then be washed in water and prepared in glycerin. 

 In preparations of mesentery of the frog or of a small mamma- 

 lian animal in bichromate of potash, the nuclei may be readily 

 recognized, not only i.i profile, but on the surface of the small 

 vessels. 



The Intima. The anatomical relations of the intima, i. e., 

 of the internal longitudinal fibres, and the elastic membrane, 

 may be studied either in sections or in the fresh state. In 

 large arteries, the best method is to immerse the vessel in one 

 per cent, solution of bichromate for several days. The intima 

 is then peeled off in thin strips, which are teased in the same 

 liquid and covered with glycerin. This is the only way of 

 showing the elastic network or the fenestrated membrane 

 which exists in certain arteries. In vessels of inacroscopical 



