216 BACTERIOLOGY. 



to stain all bacteria very intensely the tubercle bacilli 

 as well 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 bacilli will be ob- 

 served. While all other organisms in the preparation 

 will give up their color and become invisible, the tubercle 

 bacilli retain it with marked tenacity. They stain with 

 great difficulty, but once stained they retain the color 

 even under the influence of strong decolorizing agents. 



The only other organism possessing a similar pecu- 

 liarity is the bacillus of leprosy, with which, under 

 ordinary conditions, we are not likely to come in con- 

 tact. This micro-chemical reaction therefore serves as 

 a means of differentiating this organism in sputum and 

 other fluids from the body of suspected subjects from 

 all other bacteria that are likely to be present. 



SUSCEPTIBILITY OF ANIMALS TO TUBERCULOSIS. 

 The animals which are known to be susceptible to the 

 tubercular processes are" man, apes, cattle, horses, sheep, 

 guinea-pigs, pigeons, rabbits, cats, and field mice. 



White mice, dogs, and rats possess immunity against 

 the disease. 



We have reviewed the three common pathogenic 

 organisms with which we may come in contact in the 

 sputum of tuberculous individuals. Occasionally other 

 forms may be present. The pyogenic forms are not 

 rarely found, and for a long time after diphtheria the 

 bacillus of Loffler is known to be demonstrable in the 

 pharynx. These latter organisms will be described 

 under their proper heads. 



