LABORATORY EQUIPMENT AND METHODS 45 J 



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-fluids, 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. 454). 



Collecting and preparing material for use in the 

 laboratory. As directions have been given in the " tech- 

 nical notes ' ' scattered through the book for the collecting 

 and preparing of all 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 speci- 

 mens by injection, etc. Specimens to be used for dissec- 

 tion should be kept in alcohol of 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- 

 arations of French gelatine, but white glue will answer 



