THE ACID FAST GROUP 373 



is not impossible to produce disease in humans, for example, 

 by means of bovine bacilli. The facts will be considered 

 below. 



Tuberculosis is usually the cause of more deaths in man 

 in the United States annually than any other disease. The 

 disease in cattle is widely distributed, particularly in dairy 

 animals both in Europe and America. Swine, particularly 

 those which run with the cattle, are often infected. The 

 disease occurs occasionally in the horse and in the sheep. 

 Tuberculosis of the domestic fowl is common in certain dis- 

 tricts in the United States. 



Morphology. — The Mycobacterium tuberculosis is a 

 slender rod, frequently somewhat bent and with rounded 

 ends. Not infrequently the protoplasm stains somewhat 

 irregularly, giving a beaded appearance to the cell. Spores 

 and capsules are not produced. It is Gram-positive and is 

 nonmotile. The cells vary from .2 to .5/i in diameter and 

 1.5 to 3.5m in length. When grown upon certain culture 

 media elongated and branched forms are not at all uncom- 

 mon. The organism is best stained with one of the more 

 powerful analine dyes, such as carbol fuehsin. Apparently 

 the acid fastness of this organism is due to the presence of 

 a waxlike material in the cell walls. 



There is some difference of opinion as to whether there 

 are noteworthy differences in the morphology of the 

 varieties of the tubercle bacillus. It has been claimed that 

 organisms from bovine cases are somewhat shorter, 

 straighter and thicker than those from human cases and 

 are somewhat less apt to show the granular staining char- 

 acteristic. The varieties, however, are much more satis- 

 factorily differentiated by the use of cultural, physiological 

 and pathological tests. 



Cultural Characters. — The tubercle bacillus, at least 

 when first isolated from the body, requires special media 

 for its growth. Pure cultures may be secured by -rubbing 



