6 INTRODUCTION. 



the mixture measures 94 cc. While not absolutely correct, 

 the result is close enough for practical purposes. 



Formol. This is a 40% solution of formaldehyde, and 

 for use this should be reduced by addition of water to a 

 2% or 3% solution (i.e., 1 part formol to 49 or 33 parts of 

 water) ; in which specimens may be kept in good condition 

 for some months. The same care must be exercised as 

 with alcohol to change the fluid frequently while hardening 

 the specimens. Formol has the disadvantage of evaporat- 

 ing readily, and so the jars must be tightly sealed. It also 

 has the disadvantage of freezing. 



A second substitute for alcohol is Wicker sheimer'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 w r hite 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. 

 This fluid has been highly recommended, but it is now 

 little used, formol taking its place. 



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 or by a large rubber bulb. 

 It is, however, more satisfactory to use the regular inject- 

 ing syringe, sold by all dealers in naturalists' supplies. 

 These are provided with small tubes (canulas) for insertion 

 into the vessel to be injected, and these are grooved at 



