510 HISTOLOGY 



2. Carmirfe Injection Mass. Dissolve i gm. of carmine in i c.c. of 

 strong ammonia plus a little water; dilute with 20 c.c. of glycerin. Add i 

 gm. of common salt dissolved in 30 c.c. of glycerin. To the whole solu- 

 tion add an equal quantity of water. 



WARM INJECTION MASSES. 



1. Berlin Blue. Allow clear sheets of best French gelatin to swell 

 up for i or 2 hours in double the quantity of water. Dissolve by warming 

 gently over a water-bath and add, stirring constantly, an equal volume 

 of a warm solution of Berlin blue prepared as directed above. Filter 

 through flannel wrung out in hot water. 



2. Carmine. This is the best injection mass to use, but it is very 

 difficult to prepare. Dissolve 2 to 4 gm. of the best carmine in the re- 

 quired amount of ammonia. Filter and stir into 10 to 50 gm. of a filtered 

 warm solution of gelatin, prepared over the water-bath as described 

 above. Then add 25 per cent, acetic acid, drop by drop, stirring con- 

 stantly, until the mass becomes bright red and loses its ammoniacal odor. 

 If too much acetic acid is added a precipitate forms and the mass is spoiled. 

 Filter through warm flannel. 



Organs injected with a cold mass are put into 80 alcohol. After a 

 few hours they may be cut into pieces. After injection with a warm 

 mass, the specimen is put into cold water to hasten the solidification of 

 the gelatin, and then transferred to 80 per cent, alcohol. Imbed in cel- 

 loidin. Thick sections are necessary in order to follow the course of the 

 vessels. 



Prepared injection masses for use, cold or warm, are sold by dealers 

 in microscopical supplies. 



Many ingenious injection methods have been devised, such as the 

 injection of small living embryos by allowing ink to enter the veins and 

 be distributed through the body by the action of the heart; and vessels 

 have been injected with milk, after which frozen sections were stained 

 with Scharlach R. 



SPECIAL METHODS. 



The following special methods are included because of their funda- 

 mental importance. For the many other special methods which are oc- 

 casionally of service, reference should be made to the works on technique 

 mentioned at the beginning of this section. 



Weigert's Method for Staining Myelin Sheaths. This is a method for 

 the differential staining of the myelin sheath of nerve fibers and is much 

 used in the study of the normal and pathological histology of the central 



