1894.] MICROSCOPICAL JOURNAL. 269 



removing a portion of the thoracic aorta from a recently 

 killed rat, slitting it open, placing it in a saucer of silver 

 nitrate solution (1 to 300), and exposing to direct sun 

 light. It is necessary to keep the tissue in motion dur- 

 ing the entire exposure. Wash, mount in balsam, the in- 

 ternal face of the artery upward. 



The smaller arteries may be studied in a transparent 

 membrane. Fix the mesentery or the omentum in 2 

 per cent bichromate, wash, spread on a slide, stain with 

 haematoxylin, mount in balsam. The internal elastic 

 membrane will be* visible in a great many organs when 

 the vessels have been sectioned transversely. . . . 



VEINS. 



On account of the differences in the structure of veins, 

 many preparations must be made from different vessels. 

 Employ the same processes as for the arteries. 



CAPILLARIES. 



The structure and arrangement of the capillary net 

 work can be well studied only by injections. We will 

 examine the instruments used to make an injection, the 

 injection masses and methods 



Instrumeiits. — A good syringe is the simplest and most 

 useful. Among the numerous models choose one hold- 

 ing about 250 grammes. The canulas should be fastened 

 in place by friction ; those that screw on are detestable. 

 It is well to have a supply of cylindrical canulas with a 

 neck at the free end for fastening the ligature. . . . 



Injection material. — From the great number of these 

 we select the two which are most frequently used, the 

 Prussian blue gelatine and the carmine ; we advise be- 

 ginners to use the former. 



Soluble Prussian blue inass. — Soluble Prussian blue 

 may be purchased of the dealers, or prepared as follows: 

 Make these two solutions (1) — Distilled water, 1000 

 grms. ; sulphate of iron, 50 grms. (2) — Distilled water, 



