422 APPLICATION OF METHODS OF BACTERIOLOGY 



in this direction, but complete immunity has not as yet 

 resulted. 



We have reviewed the three common pathogenic organ- 

 isms that may be encountered in the sputum of tuberculous 

 individuals. Occasionally other species may be present. 

 The pyogenic forms are not rarely found, and for some time 

 after an attack of diphtheria the bacillus of Loffler is demon- 

 strable in the pharynx, so that it, too, may be present under 

 exceptional circumstances. 



Organisms with which Bacteriuin Tuberculosis may be Con- 

 fused. — It is important to note that in the study of tubercu- 

 losis one may fall into error unless it be borne in mind that 

 there is a group of micro-organisms whose members are in 

 many respects so like the genuine bacillus tuberculosis as 

 easily to be mistaken for it. While its peculiar micro- 

 chemical reaction is usually sufficient for identification, par- 

 ticularly in connection with human pathological lesions, it is 

 well to remember that the confusing organisms are not only 

 characterized by the same staining peculiarities as bacillus 

 tuberculosis, but may readily be mistaken for it on morpho- 

 logical grounds also. Furthermore, while not all the mem- 

 bers of this group are capable of causing disease, some of 

 them are pathogenic for the same animals that are suscep- 

 tible to true tubercular infection; and there may produce in 

 those animals lesions which are distinguishable from genuine 

 tubercles only by their finer histological structure. A few 

 words concerning some of these varieties, with a brief 

 summary of their more important peculiarities, may not 

 be out of place. 



Bacterium Lepr.<e. — ^Between 1879 and 1881 there was 

 described by Hansen and by Neisser an organism, a bacillus, 



