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 

 .^ 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 

 1J 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 2J 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 cannulae 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 



