312 



THE TUBERCLE BACILLUS 



Appearance of the bacilli in stained preparations. 



In stained preparations, tubercle bacilli vary in length from 2-5/A and in 

 breadth from 03-0'5/x. They are generally of the same thickness throughout. 

 In some preparations the bacilli are homogeneous, while in others they appear 

 as though composed of a number of small oval or rounded grains separated 



FIG. 198. 



FIG. 199. 



FIG. 198. From a culture, 20 days old, on inspissated horse serum, of a 

 mammalian virus of low experimental pathogenicity to bovines and rabbits 

 and of vigorous cultural growth. The virus was isolated from a human being. 

 The bacilli are very short ; some of them show a central constriction. The 

 clump at the bottom of the figure illustrates the tendency of mammalian bacilli 

 to stick together and the difficulty of separating them by emulsification. The 

 bacilli from serum cultures of this virus proved shorter than the average vigor- 

 ously growing bacillus of human origin. This figure illustrates the impossibility 

 of distinguishing with certainty, under the microscope, " human " from 

 " bovine " bacilli. Carbol-fuchsin. x 2150. (Eastwood.) (See footnote 

 p. 295.) 



FIG. 199. From a culture, 22 days old, on glycerinated broth, of a typical 

 mammalian virus of low pathogenicity to experimental animals and of vigorous 

 cultural growth. The virus was isolated from a human being. The bacilli, 

 obtained from a copious growth, are for the most part long and curved, and 

 with a tendency to beading. Carbol-fuchsin. x 2150. (Eastwood.) (See 

 footnote p. 295.) 



FIG. 200. 



FIG. 201. 



FIG. 200. From a culture, 44 days old, on glycerin-agar, of a mammalian 

 virus which was isolated from the bronchial gland of a human being. The 

 occurrence of branched forms of the mammalian tubercle bacillus in cultures 

 obtained from ordin.ary media, such as glycerinated agar, broth, or potato, is, 

 in Eastwood's experience, extremely rare. The figure also shows other forms 

 of bacilli, some very long, some very short, and many with globular or oval, 

 darkly stained bodies variously situated. Bacilli with such appearances as these 

 are common in agar cultures. Carbol-fuchsin. x 2150. (Eastwood.) (See 

 footnote p. 295.) 



FIG. 201. Tubercle bacilli from milk obtained from the udder of a cow, 

 which had received an intra-mammary inoculation with a typical bovine 

 virus. The bacilli are of various lengths ; many of them are curved and 

 regularly beaded. The bacilli here shown are such as are commonly met with 

 in cow's milk ; it would obviously be impossible for anyone to decide, on 

 morphological grounds, that they were of bovine rather than of human origin. 

 Carbol-fuchsin. x 2150. (Eastwood.) (See footnote p. 295.) 



