DIFFERENTIAL DIAGNOSIS. 305 



aniline oil and carbolic acid. They are employed in 

 the solutions to about the point of saturation. (For 

 the exact proportions see chapter on Staining-reagents.) 

 Under the influence of heat these solutions are seen 

 to stain all bacteria very intensely — the tubercle bacilli 

 as weH as the ordinary forms. If we subject our prep- 

 aration, which may contain a mixture of tubercle bacilli 

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

 another peculiarity of the tubercle bacillus will be ob- 

 served. 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 decolor- 

 izing-agents. 



ORGANISMS WITH WHICH THE BACILLUS TUBERCU- 

 LOSIS MAY BE CONFUSED. 



Differential Diagnosis. — AVhile its peculiar 

 micro-chemical reaction is usually considered to he 

 diagnostic 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 prepuce and upon 

 the vulv^a, both normally and in disease, and the so- 

 called bacillus of syphilis, described by Lustgarten as. 



