APPENDIX. 343 



sides, the advantage of not requiring heat, which in the 

 case of some forms causes a softening of the walls of the 

 blood-vessels. 



Starch Injection Mass. Grind together in a mortar one 

 volume of dry starch, one of a 2|$ aqueous solution of chloral 

 hydrate, and one-fourth volume each of 95$ alcohol and 

 of the "color." The "color" consists of equal volumes 

 of dry color (vermilion, chrome yellow, Prussian blue, etc.) 

 glycerine and alcohol. The mixture will keep indefinitely, 

 but requires thorough stirring before use and quick usage, 

 as the starch and color settle rapidly. 



Gum Injection Fluid. Make a rather thick solution of 

 gum arabic in water ; color it with carmine or soluble Prus- 

 sian blue, and strain through muslin. With the addition 

 of a little thymol the fluid will keep well if tightly corked. 

 After injection, place the animal in alcohol, which hardens 

 the gum. 



By using both injection masses in succession the complete 

 circulatory system may be injected (double injection). To 

 accomplish this, first inject with the gum fluid, colored blue, 

 and then follow with the starch mass colored red. The gum 

 will flow through the finest vessels, but the starch mass will 

 stop at the capillaries. 



Study of Vertebrate Brains. If material be abundant, 

 the study of the brain and its nerves will be much facili- 

 tated by putting heads of the various forms in the fluid 

 mentioned below a week or two before the dissection is to 

 take place. The fluid, which should be changed two or 

 three times, softens (decalcifies) the bones, and at the 

 same time hardens the nervous structures. It is composed 

 of equal parts of 95$ (commercial) alcohol and 10$ nitric 

 acid. The heads should be washed for an hour or two 



