162 PRACTICAL HISTOLOGY. 



especially if a slip of glass is fitted into the small 

 piece of cork, so as to support the tongue and pre- 

 vent the thin membrane from bulging downwards. 



METHOD OF INJECTING THE BLOODVESSELS. 



Before leaving the subject of the bloodvessels the 

 best mode of filling them with transparent material 

 may be described, especially as in the study of the 

 several organs it is necessary, in order that the course 

 and arrangement of the vessels may be properly made 

 out, that sections of injected as well as of uninjected 

 preparations should be looked at. It will be conve- 

 nient in this place to describe the injection of a small 

 animal entire from the aorta, reserving any special 

 directions concerning organs which are not thereby 

 properly injected, such, for instance, as the lungs and 

 liver, until they are severally dealt with. 



Preparation of the injection mass. This is 

 almost always a solution of gelatine colored, either 

 red with finely precipitated carmine, or blue with 

 soluble Prussian blue. Sometimes, but rarely, when 

 it is wished to inject two sets of vessels of different 

 colors, both of these are used, but as a rule all the 

 bloodvessels arteries, capillaries, and veins should 

 be filled with the same injecting fluid; preparations 

 in which the arteries are filled with one color and 

 the veins with another are pretty to look at, but are 

 difficult to prepare, and present no practical advan- 

 tage. The gelatine solution is made as follows: 

 Ten grammes of clear gelatine are cut into small 

 pieces, and placed in a beaker of cold distilled water 

 to soak. In about an hour the gelatine will have 

 swollen to several times its original volume. The 

 excess of water is now poured off, a glass cover put 

 over the beaker, and it is placed in a water-bath and 

 heated until the gelatine is rendered fluid. 



For the red injection four grammes of carmine are 

 rubbed up in a mortar with eight cubic centimetres 

 of liquor ammonise, and then fifty cubic centimetres 



