with fuchsin). To secure thorough staining of all ba- 

 cilli present it is advisable to expose the section to the 

 staining-fluid for twenty-four hours. 



Stained by this method the bacilli can be detected in 

 sputum with an ordinarily good one-fifth inch objective 

 (giving 250 to 300 diameters) and simple central illu- 

 mination without condenser ; though for critical exami- 

 nation, especially in tissues, higher powers (400 to 600 

 diameters) and special illumination are desirable. It is 

 already demonstrated that the presence of these bacilli 

 has decided diagnostic value, not only in sputum but also 

 in pus from laryngeal ulcers, from cold abscesses, from 

 joint cavities, and in urine. 



The bacilli of leprosy may be stained in fresh sections 

 with the ordinary two per cent, aqueous solutions of the 

 aniline colors, without special preparation ; if the tissue 

 has been long exposed to alcohol it is desirable to place 

 the sections for a few minutes in a five per cent, watery 

 solution of acetic acid, and then transfer them to a ten 

 per cent, solution of caustic potash. After washing in 

 water they may be then stained with the ordinary fuchsin 

 solution. 



The micrococci of gonorrhoeal pus require no special 

 treatment ; the cover-glass on which the pus is dried and 

 heated (as already directed) is treated for five to ten min- 

 utes with the two per cent, solution of methylene blue. 



For cutting extremely thin sections of lung and other 

 delicate tissues, the following method of imbedding is 

 well adapted : 1 The tissue lies for twenty-four hours in 

 the ordinary clearing solution (one part of carbolic acid 

 and four of turpentine); it is then transferred for twenty- 

 four hours to a saturated solution of paraffin in turpentine, 

 after which it may be imbedded either in pure paraffin 

 or in one of the many mixtures of this substance with 

 tallow oil. 



1 For a knowledge of this method, and of other valuable points in histological 

 technique, I am indebted to the rare technical skill and extensive experience of my 

 friend Dr. W. T. Councilman, Fellow (by courtesy) of the John* Hopkins Uni- 

 versity, Baltimore. 



