STAINING OF BACTEKIA IN TISSUES. 143 



neither interferes with their structure nor prevents their 

 being cut into sections. They must be " imbedded," as 

 this process is called. 



Imbedding in celloidin. Most convenient for this 

 purpose is celloidiu, a body somewhat similar to col- 

 lodion, soluble in a mixture of equal parts of alcohol 

 and ether, as well as in absolute alcohol. 



Two solutions of celloidin are to be employed, the one 

 a thin solution in a mixture of absolute alcohol and 

 ether, equal parts, the other a thick solution in absolute 

 alcohol. Into the thin solution the tissue is placed from 

 absolute alcohol, and allowed to remain for twenty-four 

 or forty-eight hours. It is then placed in the thick 

 solution for one or two days. From this it may be 

 removed and placed immediately upon a bit of cork. 

 The adherent celloidin will act as a cement, and as it 

 hardens rapidly, the tissue is soon fast to the cork ; after 

 remaining in 60 per cent, alcohol for twenty-four hours 

 to complete the solidification of the celloidin, sections 

 may be cut as in the way just described for tissues not 

 so treated. 



The paraffin method of imbedding is not to be recom- 

 mended for bacteriological purposes. 



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 Loffler, 

 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 



