INJECTIONS. 415 



solution. The efferent vessels may be tied to cause the smaller side branches 

 to be filled. After the injection has been finished, the tissues may be 

 hardened in alcohol or Miiller's fluid, and sectioned in the usual way; 

 thick sections are necessary in order to follow the course of the vessels. 



Solutions of Berlin blue or India ink are the simplest injection fluids. 

 Carmine may be prepared by dissolving i gr. in the required amount of 

 ammonia and adding 20 cc. of glycerine. The solution is completed by 

 adding i gr. of common salt dissolved in 30 cc. of glycerine (or 20 drops of 

 hydrochloric acid in 20 cc. of glycerine). The second solution is to neutral- 

 ize the first solution, since the ammoniacal fluid tends to spread through the 

 vessel walls. 



Gelatin injection masses are used while warm and fluid, and the tissues 

 which receive them must be kept warm in a water batk Clean sheets of 

 the best French gelatin are soaked in water for several hours, until soft 

 and swollen. Then they are melted over a water bath and an equal quan- 

 tity of an aqueous solution of Berlin blue, saturated or dilute as desired, is 

 stirred in. The mass is filtered through flannel wrung out in hot water, 

 and is injected while warm. 



A carmine mass may be prepared by dissolving from 2 to 4 grs. of the 

 best carmine in the required amount of ammonia. The solution is filtered 

 and stirred into filtered melted gelatin prepared as already described. 

 The amount of gelatin may be from 10 to 50 grs. Twenty-five per cent, 

 acetic acid is then added drop by drop, until the mass becomes bright red 

 and loses its ammoniacal odor. If too much acetic acid is added a pre- 

 cipitate forms and the mass is spoiled. During the process the mixture is 

 kept warm over a water bath and is constantly stirred. It is filtered through 

 warm flannel and may be used at once or allowed to cool and heated when 

 needed. 



Prepared injection masses are sold by Griibler. 



Many ingenious injection methods have been devised, such as the in- 

 jection of small living pig embryos by allowing ink to enter the umbilical 

 vein and be distributed through the body by the heart's action; or the 

 injection of vessels with milk and staining the frozen sections with 

 Scharlach R. 



THE MICROSCOPE. 



It is unfortunate that the price of a microscope is prohibitive to many 

 medical students, and that some who would otherwise purchase instru- 

 ments at the beginning of their work, wait until an official position entitles 

 them to a discount. The price of microscopes is not always quite as high 

 as is listed, and sometimes when several students buy microscopes at one 

 time they may secure lower rates by having one of their number act as agent. 



