350 BACTERIOLOGY. 



much as they are occasionally encountered under circum- 

 stances that might lead one to look for true tubercle 

 bacilli, and since they possess certain peculiarities 

 through which it has been the custom to identify 

 bacillus tuberculosis — i. e., retention of the stain when 

 acted upon by acids or alcohol, and a more or less deli- 

 cate, beaded form — the possibility of their being con- 

 founded with that organism is obvious. In consequence 

 they have received a great deal of attention during the 

 past few years. 



Space does not permit of a description of the twenty 

 odd species (?) that have been described by different in- 

 vestigators. It will suffice to say, from personal study 

 of the group, that in all jDrobability not more than three^ 

 perhaps only two, species are really represented, and 

 that the remainder may fairly be regarded as varieties. 

 As said, the characteristic common to all the mem- 

 bers of this group is that they are to greater or less 

 extent acid-proof — i. e., when once stained by the Koch- 

 Ehrlich or Ziehl process the color is not in all cases 

 removed by the ordinary acid decolorizers. In this par- 

 ticular, however, there is considerable variation. In 

 morphology some of them might readily be mistaken 

 for bacillus tuberculosis, though even these are usually 

 a trifle larger and less delicate than that organism ; 

 others are at once differentiated froui normal tubercle 

 bacilli, but have somewhat the appearance of bacillus 

 tuberculosis when degenerated or involuted ; still otliers 

 have nothing in their general appearance to lead to con- 

 fusion. 



When mixed with other bacteria, as is the case in the 

 soil, in manure, in intestinal contents, etc., their isola- 

 tion in pure culture is a matter of difficulty, and this is 



