8 INTRODUCTION. 



jection 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 

 in water before dissection, as otherwise the acid will attack 

 the dissecting instruments. 



Miiller's Fluid is also used for the preservation of 

 brains and nervous matter, but it does not decalcify. In 

 its use the cavity of the skull should be opened so as to 

 permit free entrance of the fluid. It should be changed 

 in twelve hours, one day, one week, and four weeks. 

 It colors all tissues a dirty green. Miiller's Fluid is com- 

 posed of 



Sulphate of soda 1 part 



Bichromate of potash 2 parts 



Water 100 " 



Fuchsin is one cf the most easily used stains. It is made 

 by dissolving 1 part of the aniline dye in 200 parts of 

 water. 



