282 BACTERIOLOGY. 



and other forms, to the action of decolorizing agents, an- 

 other peculiarity of the tubercle bacillus will be observed. 

 While all other organisms in the preparation will give 

 up their color and become invisible, the tubercle bacillus 

 retains it with marked tenacity. It stains with great 

 difficulty, but once stained it retains the color even under 

 the influence of strong decolorizing agents. 



ORGANISMS WITH WHICH THE BACILLUS TUBERCU- 

 LOSIS MAY BE CONFUSED. 



DIFFERENTIAL DIAGNOSIS. While its peculiar 

 micro-chemical reaction is usually considered to be diag- 

 nostic of the bacillus tuberculosis, it is well to remember 

 that there are at least three other species of bacilli which, 

 when similarly treated, react in the same way. It is of 

 importance to bear this point in mind, particularly in 

 the microscopic examination of urine and pathological 

 secretions from the genito-urinary tract and from the 

 rectum, for of the three species two are frequently found 

 in these localities, viz., the so-called smegma bacillus, 

 located in the smegma and often seen beneath the pre- 

 puce and upon the vulva, both normally and in disease, 

 and the bacillus of syphilis, described by Lustgarten as 

 contained in syphilitic manifestations, particularly in 

 primary sores. The third organism of this group the 

 bacillus of leprosy because of its rarity, is not so likely 

 to cause error in the diagnosis of troubles occurring in 

 these localities. 



According to Hueppe, the differential diagnosis be- 

 tween the four organisms depends upon the following 

 reactions : When stained by the carbol-fuchsin method 

 commonly employed in staining the tubercle bacillus the 



