HISTOLOGICAL METHODS. 



181 



the remaining -J oz. of gelatine solution, and drop this into 

 the heated carmine mixture with constant stirring. The 

 acid is added in order to precipitate the carmine and 

 prevent its diffusion through the walls of the capillaries. 

 The presence of the gelatine prevents the precipitated 

 particles from assuming a coarse granular form. For sec- 

 tion, the tissues are hardened first, in equal parts of 

 rectified spirit and water, with the addition of i per cent 

 hydrochloric acid; then in rectified spirit; and, lastly, in 

 absolute alcohol. Sections are then made, and mounted in 

 dammar. 



338. Prussian Blue and Gelatine Mass, 



( Gelatine, 33 grammes. Distilled water, 2ooCC. Dis- 

 " \ solve with the aid of a gentle heat (using a water-bath). 



( Soluble Prussian blue, 4 grammes. Distilled water, 

 B ( 3ooCC. Dissolve. 



Add B to A gradually. The tissues are hardened for 

 section and preserved, as stated in 337. 



339. Injection of Blood-vessels. Syringe. A brass 

 syringe S (Fig. 60), capable of holding from four to six 



M 



FIG. 60. Injection syringe (S)>ith mercurial manometer (M). 



ounces of fluid, is very often used "for injection. It is 

 usually provided with brass nozzles () of various sizes, for 

 vessels of different calibre, and a stopcock (s) which may 

 be separated from the nozzle and from the syringe. The 

 nozzle is tied in an artery ; the stopcock-piece is pushed 

 into it ; both are filled with injection-mass by means of a 

 pipette; and the stopcock turned. The syringe is then 

 filled care being taken to expel all air by holding the 



