PUPIL AND SCHOOLROOM EQUIPMENT 463 



and the margin bent back over it, it will strengthen the 

 dish, and make a broader and smoother edge for the hands 

 to rest on. Diagonally across the dish, about one-fourth 

 inch from the bottom, should run a thick wire. A layer 

 of paraffin one-half inch thick should cover the bottom. 

 It should be poured in melted, when the diagonal wire 

 will be imbedded in it and will hold it in place. Acids 

 must not be put into the pan. 



The reagents necessary are alcohol of 95 per cent and 

 85 per cent, and formalin of 4 per cent (the formaldehyde 

 sold by druggists is 40 per cent and should be diluted ten 

 times with water), these for preserving material for dis- 

 section; chloroform for killing specimens; glycerin for 

 making temporary microscopic mounts, and 20 per cent 

 nitric acid for preparing specimens for study of the nervous 

 system. In addition there will be needed the few other 

 materials mentioned in the following paragraphs as neces- 

 sary in the preparation of injecting-fiuids, the staining of 

 fresh tissue and preserving by special methods. 



A list of reference books desirable in the laboratory is 

 appended as a separate paragraph (see p. 466). 



Collecting and preparing material for use in the 

 laboratory. — ^As directions have been given here and there 

 through the book for the collecting and preparing 

 of the various kinds of animals chosen as subjects 

 of the laboratory exercises, it will only be necessary 

 to give here directions for making certain special mixtures 

 and for the special preparation of specimens by injection, 

 etc. Specimens to be used for dissection should be kept in 

 alcohol 85 per cent or in formalin of 4 per cent. Alcohol is 

 better for the earthworm, but for the other examples formalin 

 is either better or as good, and as it is much cheaper it may 

 well be chosen for the general preservative. 



Methyl green, a stain used for coloring fresh tissues. 

 Dissolve the methyl green powder in water, using about 

 as much powder as the water will take up. Add a few 

 drops of acetic acid. 



Injecting-masses. — Injections are best made with prep- 



