STAINING OF THE SECTIONS. 159 



is recognized by the transparent appearance that they 

 assume. From this they are placed in paraffin that is 

 melted at 53 C., and allowed to remain in this for 

 three or four hours. They are then transferred to a 

 small paper or metal mould, or a pill-box, and melted 

 paraffin is poured over them. When the paraffin has 

 become solid the mould or pill-box is removed from 

 around it, the excess of paraffin removed from about 

 the imbedded tissue, and the latter is ready for cutting. 



When the sections are cut they are freed from par- 

 affin by exposing them to turpentine ; the latter is re- 

 moved by washing in alcohol and the sections can now 

 be stained in the ordinary way. In cutting sections 

 from tissues that have been imbedded in paraffin the 

 long axis of the knife should be at nearly right angles 

 to the direction in which the knife travels. For bac- 

 teriological purposes the method of imbedding in par- 

 affin does not as a rule give such good results as when 

 the celloidin method is employed. In this work, there- 

 fore, the latter is usually preferred. 



STAINING OF THE SECTIONS. The sections when cut 

 may be stained in a variety of ways. The ordinary 

 watery solutions of the three common basic aniline dyes 

 fuchsin, gentian-violet, or methylene-blue or, what 

 is better, the alkaline methylene-blue solution of Loeffler, 

 may be employed for general use. 



The acid aniline dyes, as well as some of the vege- 

 table coloring matters, are essentially nuclear stains, and 

 are not applicable to the staining of bacteria. 



Into a watch-glass containing either of the staining 

 solutions mentioned, the sections are to be placed after 

 having been in water for about one minute. They 

 remain in the staining solutions for from five to eight 



