712 



Tuberculosis 



only in dusts with which pulverized sputum was mixed, and 

 to be most common where the greatest uncleanliness pre- 

 vailed. 



Morphology. The tubercle bacillus is a slender, rod- 

 shaped organism with slightly rounded ends and a slight 

 curve. It measures from 1.5 to 3.5 [A in length and from 

 0.2 to 0.5 fJ- in breadth. It commonly occurs in pairs, which 

 may be associated end to end, but generally overlap some- 

 what and are not attached to each other. Organisms found 

 in old pus and sputum show a peculiar beaded appearance 

 caused by fragmentation of the protoplasm and the presence 



Fig. 237. Bacillus of tuberculosis, showing branched forms with invo- 

 lution (Migula). 



of metachromatic granules. These fragmented forms have 

 been thought to be bacilli in the stage of sporulation, and 

 Koch originally held this view himself, though later researches 

 have not confirmed it. 



The tubercle bacillus forms no endospores. The frag- 

 ments thought by Koch to be spores are irregular in shape, 

 have ragged surfaces, and are without the high refraction 

 peculiar to spores. Spores also resist heat strongly, but the 

 fragmented bacilli are no more capable of resisting heat 

 than others. 



The bacilli not infrequently present projecting processes 

 or branches, this observation having changed our views 



