THE PREPARATION OF ANIMAL TISSUES. 61 



The Injection of Blood Vessels. 



Blood and lymphatic vessels are more satisfac- 

 torily demonstrated when filled. The former are 

 better injected with a fluid which becomes solid in 

 ordinary temperatures. The vessels must be fully 

 distended at the time and this distention must 

 remain. Gelatine forms the foundation of injection 

 masses for the above purposes, because it can be 

 liquefied at blood heat and it solidifies in a little 

 lower temperature; then, again, it is capable of 

 being easily cut, and does not become brittle, but 

 remains tough and resistant, though sufficiently 

 soft. Injections of different colours are employed 

 in order that the arteries may be distinguished 

 from the veins, and these again from other 

 channels, such as bile ducts, lymphatic vessels, 

 capillaries, &c. 



The distribution of the capillary vessels, indeed, 

 in many cases cannot be satisfactorily studied or 

 demonstrated without injection or other special 

 modes of preparation. Injections of single organs, 

 or parts carefully dissected from the body of an 

 animal, all the larger arteries and vessels being 

 carefully tied, can be made ; whilst the entire 

 blood system of mammalian animals, including 

 man, of birds and reptiles, can be injected from an 

 arterial trunk, so that the finest capillary vessels 

 shall be perfectly filled. 



Red Mass. 



This is made of gelatine coloured with carmine. 

 In making it the greatest care must be exercised in 



