Morphology 657 



of the organism, and the lesions it produces, as to be almost without 

 a parallel in medical literature. 



Distribution. So far as is known, the tubercle bacillus is a 

 purely parasitic organism. It has never been found except in the 

 bodies and discharges of animals affected with tuberculosis, and 

 in dusts of which these are component parts. This purely parasitic 

 nature interferes with the isolation of the organism, which cannot 

 be grown upon the ordinary culture-media. 



The widespread distribution of tuberculosis at one time sug- 

 gested that tubercle bacilli were ubiquitous in the atmosphere, that 

 we all inhaled them, and that it was only our vital resistance that 

 prevented us all from becoming its victims. Cornet,* however, 



** /^'Vr'i'l' 

 i&i&M?. 



Fig. 269. Tubercle bacillus in sputum (Frankel and Pfeiffer). 



showed the bacilli to be present only in dusts with which pulverized 

 sputum was mixed, and to be most common where the greatest 

 uncleanliness prevailed. 



Morphology. The tubercle bacillus is a slender, rod-shaped 

 organism with slightly rounded ends and a slight curve. It meas- 

 ures from 1.5 to 3.5 IJL in length and from 0.2 to o. 5 jj, in breadth. 

 It commonly occurs in pairs, which may be associated end to end, 

 but generally overlap somewhat 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 of metachromatic granules. The tubercle bacillus 

 forms no endospores. 



The fragments, originally 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 



* "Zeitschrift fur Hygiene," 1888, v, pp. 191-331. 



42 



