i HINTS ON DISSECTION 13 



strong thread. Place this in the dish with the lead (which 

 is simply to keep the cork-board from floating in .water) 

 downwards. Or, place a few strips of sheet lead in the 

 bottom of the dish, and then pour in some melted paraffin- 

 wax into which a little lamp-black has been stirred, so as 

 to make a layer half an inch or more in thickness. 



For larger animals than the frog, in addition to a larger 

 dish, a dissecting -board will also be required. Get a piece of 

 soft deal or pine about 18 inches x n inches and inch 

 thick, and nail round its edge a strip of wood about J inch 

 X i inch, so as to form a projecting rim. 



9. A magnifying glass. Any good pocket-lens or a com- 

 mon watchmaker's glass will answer the purpose. As it 

 is often desirable to have both hands free while using the 

 lens, a stand of some kind is useful. One of the simplest is 

 made by fixing a piece of J-inch brass-tubing, about 6 inches 

 long, into a heavy block of wood, about 3 inches in diameter, 

 and coiling roujid it, in a close spiral, one end of a piece of 

 thick wire, which can be raised and lowered on the tube ; 

 leave 6 or 7 inches of the wire standing out at right angles, 

 and bend the free end into a loop to carry the lens. Or, 

 get a piece of narrow clock-spring, about 13 inches long, and 

 rivet one end to the outside of the rim of a watchmaker's 

 glass, and the other to a small piece of zinc or brass ; on 

 passing the spring round the head, the lens is kept in place 

 at the eye without exertion. 



10. Medium and small-sized pins. Large blanket pins 

 are useful for fixing down larger animals. 



11. A small sponge and a duster. 



12. One or more wide-mouthed bottles or jars, containing a 

 preservative in which to place your subjects after each day's 

 work. The most convenient preservative for the purpose in 

 most cases is the fluid sold as formaline, 1 which can be 

 diluted as it is wanted. For preserving your dissections 

 from day to day, a i per cent, solution of formaline is strong 

 enough in many cases i.e., i cubic centimetre of formaline 

 to 99 c.c. of water, or three-quarters of a dram of formaline 

 to half a pint of water. For permanent preservation, a 

 stronger solution 2 to 5 per cent., according to circum- 

 stances should be used, or methylated spirit. If formaline 

 is not available, use strong methylated spirit (i.e., about 

 90 per cent.) diluted with one-third of its bulk of water. 



13. A plentiful supply of clean water. 



14. An ounce or two of chloroform. 



A 40 per cent, solution of the gas formic aldehyde. 



