136 THE FROG chap. 



b. Absolute alcohol, 

 I . Turpenlinc. 



d. Paraffin: sold in two grades, "hard" and "soft.'' It is best to 

 get an ounce or two of each. 



c. A solution of Canada balsam in chloroform or turpentine. This 

 should be kept in a small glass bottle, with a ground glass cap — not a 

 stopper or cork. 



/ A solution of alcoholic borax-carmine. This may be bought ready 

 mixed, or made as follows : — Grind up in a mortar 2 grammes of car- 

 mine and 4 grammes of borax, and dissolve in lOO c.c. of distilled 

 water : to this solution add an equal volume of 70 per cent, alcohol : 

 allow to stand for a day or two and filter. 



g, A water-bath, in which melted paraffin may be kept at a constant 

 temperature. For a make-shift you can use a saucepan with a flat 

 piece of tin over it ; fill the saucepan about half full of water, and 

 heat it over a spirit lamp or a small oil-lamp or gas-burner, regulating 

 the distance of the flame so as to keep the temperature of the water at 

 about SS°C. (131° F.). 



h. Two or three watch-glasses or other small shallow vessels for con- 

 taining melted paraffin. 



i. A sharp, flat-ground razor. 



j. A section-lifter, made by beating out flat about half an inch of the 

 end of a piece of stout copper wire, about 6 in. long, and bending the 

 flattened portion at an obtuse angle with the rest. 



Preparation of Tissues for Section Cutting. 



a. Fixing, hardening, and decalcifying. 



Sections may be cut from specimens which have been carefully pre- 

 served in alcohol, — first in 70 per cent., and after a day or two trans- 

 ferred to 90 per cent. But certain other reagents are more effective in 

 effecting ihe. fixing of the tissues — i.e., in quickly killing and coagulating 

 the protoplasm of the cells with a minimum of shrinkage, and of these 

 the one most generally useful is a solution of corrosive sublimate (see 

 above), in which, from a freshly-killed frog, place small pieces of the 

 various organs and tissues to be examined — e.g., skin, intestine, stomach, 

 liver, pancreas, kidney, ovary, testis, and spinal cord, as well as 

 the inner half of the eyeball. The intestine and stomach should be 

 first washed out in salt solution, and then cut into pieces about § inch 

 long ; the liver should be [cut into pieces not more than \ inch cube. 

 After about half-ari-hour to two hours, according to the size of the 



