ON INJECTION xix 



The colouring matter used must not be soluble in any of 

 the fluids in which the specimen is afterwards to be dissected, 

 hardened, or preserved. The most convenient are French 

 blue, Prussian blue, vermilion, and carmine. 



In the case of the larger animals, freshly prepared plaster 

 of Paris forms, if coloured, a convenient substance for injec- 

 tion : it solidifies in the vessels, and so does not escape if a 

 vessel is accidentally cut during the dissection. 



For smaller animals, thick gum-water or white of egg 

 may be injected cold, or a jelly made of gelatine and water 

 injected warm : the animal should afterwards be put into 

 alcohol to harden the injection. If the animal is not to be 

 dissected after injection, water coloured with any of the above' 

 pigments may be used with advantage, and this method is 

 particularly useful for the alimentary and excretory systems 

 of the Hver-fluke. 



For injecting small animals, a suitable syringe consists of 

 a glass tube with an india-rubber cap fitted on one end, the 

 other end being drawn out to a point sufficiently fine to 

 enter the vessel to be injected. After the tube is drawn out 

 in the flame and cut off, its sharp edges must be shghtly 

 roimded off by holding for a moment in the flame. Several 

 such cannulse of various sizes should be kept ready. 



For injecting larger animals, such as a rabbit, with plaster 

 of Paris, the blood must first be washed out of the vessels 

 by injecting warm salt-solution. The following apparatus is 

 necessary, and must all be placed on the table ready for use 

 before the animal is killed ; for the blood coagulates after 

 death so rapidly as to allow no time to look for instruments. 



1. CannulsB : glass ones are the most convenient ; they 

 should be of various sizes, to fit the various vessels which it is 

 proposed to inject, and each should have a shght constriction 

 near the tip, so that it may be firmly secured in the vessel by 

 a ligature. The largest cannula that will enter the vessel 

 should be used. 



2. A glass syringe, capable of holding about an ounce of 

 fluid. A larger syringe is liable to get blocked up. 



3. Several pieces of strong india-rubber tubing, about an 



