PLATE XXX. 



TUBERCLE BACILLUS. 



A preparation of Tubercular sputum, distributed over the cover-glass in the fresh 

 state. Carbol fuchsin, heated on the cover, the latter then transferred to a watch 

 glass of 25 per cent, hydric sulphate till decolourized, washed in water, and then 

 counter-stained with aqueous solution of inethylene blue in the cold, washed again in 

 water, and allowed to dry. Tubercular sputum is best examined when no antiseptics 

 have been used for its- disinfection. It should be spread out in a thin layer over a 

 sheet of glass on a black surface, or one of the black-bottomed plates made for the 

 purpose; the most purulent foci are then isolated with needle and forceps, or cut out 

 with scissors and forcibly broken up and distributed on a series of cover-glasses with 

 the back of the forceps, whilst the covers are steadied by the pressure of a needle. 

 Passing the films through the name is not necessary. If the cover-glasses are not 

 heated after the carbol fuchsin has been filtered on to them, the dye must be allowed to 

 act for a considerably longer time fifteen minutes: if heated, they must be held over 

 a low flame in a small pair of forceps of which the ends have been somewhat sharply 

 bent, in order that the dye may not be conducted to the under side of the glass. 



The rationale of this particular method is as follows: the carbol fuchsin stains all 

 the different microbes present ia such a film ; with the exception of the tubercle 

 bacilli, all are afterwards decolourized by the action of the hydric sulphate, to be 

 re-dyed, together with the cell nuclei, by the methylene blue. This peculiar resistance 

 to the action of the acid is common to the tubercle, leprosy, and smegraa bacilli. 



In the examination of pure cultures of the bacillus, this differential method is 

 unnecessary, and the organism may be stained simply with carbol fuchsin, or by 

 Gram's method, etc. 



In addition to the " polynuclear" leucocytes (pus cells), there are shown in the 

 figure two squamous epithelial cells derived from the upper part of the respiratory 

 passages ; the body of these is faintly tinted with the blue. 



Many of the tubercle bacilli occur in small grotesque groups, that have been 

 likened to Chinese characters. 



The bacilli are mostly slightly curved, their extremities rounded, and their proto- 

 plasm segmented, so that the microbes appear " beaded." The beading is not invariable 

 in such preparations of sputum. 



