166 Modern Microscopy 



the acid to the remaining half of gelatine, and drop it little 

 by little into the carmine mixture, stirring well all the time 

 ■with a stick or glass rod. Filter through flannel, and add 

 a few drops of carbolic acid to make the mass keep. The 

 principle to be remembered in making this mass is this: 

 the carmine, if alkaline, would diffuse through the vessels 

 and stain the tissues around them ; if acid, the carmine 

 would be deposited in fine granules, which would block up 

 the capillaries ; hence the necessity for a neutral fluid. 

 The best guides are the colour and smell of the fluid. It 

 should be a bright red, and all trace of smell of ammonia 

 must be removed. The gelatine solution is made by putting 

 1 ounce of gelatine into 6 ounces of water ; it must then be 

 left until the gelatine becomes quite soft ; then dissolve over 

 a water-bath. 



Prussian or Berlin Blue and Gelatine Mass. — Take 

 IJ ounces of gelatine, place it in a vessel and cover it with 

 water ; allow it to stand until all the water is absorbed and 

 the gelatine is quite soft. Then dissolve in a hot-water 

 bath. Dissolve 1 dram of Prussian or Berlin blue and 

 1 dram of oxalic acid in 6 ounces of water, and gradually 

 mix it with the gelatine solution, stirring well all the time ; 

 then filter through flannel. 



Watery Solution of Berlin Blue. — Dissolve 1^ drams 

 of the blue in 18 ounces of distilled water and filter. This 

 fluid is useful for injecting lymphatics. 



Injecting Apparatus Required. — An injecting syringe 

 fitted with a stop-cock, and several cannulse of various 

 sizes. 



Directions for Injecting. — The animal to be injected 

 should be killed by chloroform, so that the vessels may be 

 dilated, and injected while warm ; if possible it should be 

 placed in a bath of water at a temperature of 40° C. 

 Expose the artery of the parts to be injected, clear a small 

 portion of it from the surrounding tissues, and place a 

 ligature of thin twine or silk round it. With sharp scissors 

 make an oblique slit in the wall of the vessel, insert the 



