METHODS OF STUDY. 95 



tissues are perfectly imbedded in the coagulated blood. 

 Sections cut b}^ a mechanical microtome, from heat-coagulated 

 larvae imbedded in paraffin, were prepared in the following 

 manner. 



2. Imbedding. — Heat-coagulated larvae are cut longitudinally 

 or transversely and placed in absolute alcohol for two or three 

 days, transferred to chloroform, and left until they sink. I 

 adopt the following modification of Giesbrecht's method :* 



The chloroform is gradually saturated with fragments of hard 

 paraffin. When it will dissolve no more it is placed in an oven 

 and gradually heated, adding paraffin a small piece at a time, 

 until the temperature of 130° Fahr. is reached ; the chloroform 

 evaporates slowly, and sufficient paraffin must have been added 

 in the process to prevent rapid evaporation. The concluding 

 stages are performed in an open vessel. In twenty-four hours 

 or longer the last traces of chloroform have been removed. 

 The imbedding mass is allowed to cool, and the specimen is 

 cut out and prepared for the microtome. 



The specimen must be placed in position before the paraffin 

 is allowed to cool. 



It is important to perform the w^hole operation at as low a 

 temperature as will melt the paraffin. Any undue rise of 

 temperature will render the integument horny and destroy the 

 specimen. 



All my serial sections were made with the Cambridge rocking 

 microtome. 



3. Stainmg and Mounting-. — Staining is most satisfactorily 

 effected after cutting the sections. I adopt the following pro- 

 cess, which leaves nothing to be desired : 



I. The section ribbon should be attached to the glass slip 

 with equal parts of white of Q%g and glycerine, Mayer's 

 formula. t I effect this as follows : 



I spread a thin film of glycerine albumen on the slip by a 

 camel's hair pencil, which has been previously wetted with 

 distilled water. If not wetted the glycerine albumen becomes 



* Zool. Anzeig., p. 483, vol. iv., 1881. 



t Journ. of Roy. Mic. Soc, new series, iv., p. 317, 1SS4. 



