342 ELEMENTS OF COMPARATIVE ZOOLOGY. 



A second substitute for alcohol is Wickersheimer's fluid. 

 This is made by dissolving 100 grams of alum, 25 of com- 

 mon salt, 12 of saltpetre, 60 of potassic carbonate, and 20 

 of white arsenic (arsenious acid) in 3 litres of boiling 

 water. To this, when cold, add 1200 grams of glycerine 

 and 300 of alcohol. Change the specimens once or twice, 

 and keep them in at least twice their bulk of the fluid. 



Injections are made as a means of more readily following 

 tubular structures, especially blood-vessels, and consist in 

 forcing into these tubes colored material which will render 

 them more easily recognized. For many injections simple 

 apparatus may be used. Thus frequently a glass tube 

 drawn out to a point can be filled with the injecting fluid 

 and then, when the end of the tube is inserted into the 

 blood-vessel, the fluid can be forced into the artery or vein 

 by the pressure of the breath. It is, however, more satis- 

 factory to use the regular injecting syringe, sold by all 

 dealers in naturalists' supplies. These are provided with 

 small tubes (canulas) for insertion into the vessel to be in- 

 jected, and these are grooved at the tip so that they may 

 be firmly tied into the artery or vein. 



Most of the injections called for in the present work 

 can be made either through the aorta or through the ven- 

 tricle. The ventricle is cut open, and the canula is forced 

 through this opening into the aorta, around which a string 

 is passed and tied, thus holding the tube firmly in place. 

 The syringe is then filled with the injecting fluid (see 

 below) and connected with the canula, when a pressure 

 upon the piston will force the fluid into the blood-vessels. 

 Too much pressure should not be exerted, as the vessels are 

 liable to rupture. 



Various injecting fluids have been proposed, but the 

 following are ample for all purposes, and they have, be- 



