TUBERCLE BACILLUS 1 97 



This is manifested by the formation of fine gray tubercles. In 

 tuberculosis of the lungs it is more than probable that the bacilli are 

 inhaled. Local tuberculosis has often followed skin inoculation, 

 either by accidental or intentional trauma. Tuberculous mothers 

 may have tuberculosis of the. genital tract, and fathers, having 

 tuberculous testes, discharge bacilli in the semen. Placental trans- 

 mission of the bacilli from mother to child occurs. 



FIG. 70. Tubercle bacilli showing involution forms. (Kolle and Wassermann.) 



Types of Tubercle Bacilli. It has been considered probable by 

 many observers that there are two types of bacilli, a human and a 

 bovine type. Theobald Smith was the first to advance this theory. 

 Koch has announced that the two types were totally different, and 

 that the human was incapable of infecting cattle, and the bovine 

 was not pathogenic for man. In view of the fact that cattle are 

 frequently tuberculous, and the bacilli are often found in the milk, 

 it is important to know if the bovine type can develop in man. 

 Ravenel has shown that it is undoubtedly pathogenic for human 

 beings. Men have been infected on the hands, while performing 

 autopsies on tubercular cattle, and their skin lesions showed, histo- 

 logically, unmistakable tubercles. Cattle have been infected by 



