MET HOD OF STAINING SPECIMENS. 37 



being slightly elevated). The water that still adheres is dried 

 off in the air or gently over the flame, and when perfectly dry 

 it is placed upon the drop of Canada balsam which has been put 

 upon the glass slide. 



In placing the cover- glass in the staining solutions one must 

 be careful to remember which is the spread side. 



By holding it between yourself and the window, and scraping 

 the sides carefully with the sharp point of the forceps, the side 

 having the specimen on it will show the marks of the instrument. 



Little glass dishes, about one-half-dozen, should be at hand 

 for containing the various stains and decolorants. 



Tissue Preparations. In order to obtain suitable specimens 

 for staining, very thin sections of the tissue must be made. 



As with histological preparations, the tissue must be hardened 

 before it can be cut thin enough. Alcohol is the best agent for 

 this purpose. 



FIG. 12. 



Spatula for Lifting Sections. 



Pieces of the tissue one-quarter inch in size are covered with 

 alcohol for 24 to 48 hours. 



When hardened it must be fixed upon or in some firm object. 

 A paste composed of- 

 Gelatine 1 part. 



Glycerine 4 parts. 



Water 2 parts. 



will make it adhere firmly to a cork in about 2 hours, or it can 

 be imbedded in a small block of paraffine, and covered over with 

 melted paraffine. Celloidin may be used as an imbedding agent, 

 and formalin is useful to harden tissue quickly. 



Cutting. The microtome should be able to cut sections JT ^ 

 inch in thickness ; this is the fineness usually required. 



The sections are brought into alcohol as soon as cut unless 

 they have been imbedded in paraffine, when they are first washed 

 in chloroform to dissolve out the paraffine. 



