Pathogenic Bacteria 339 



Early case detection can do a great deal to lower the number of 

 new infections encountered each year, and mass X-ray programs 

 are playing an important part in this type of preventive medicine. 

 The tuberculin test when found to be positive indicates that 

 tubercle organisms are present in the body. It does not necessarily 

 mean that the person has an active case of tuberculosis. Because 

 of the body's remarkable ability to wall-off foci of infection, much 

 tuberculosis does not progress past this primary stage. Practically 

 all adults have come in contact with Mycobacterium tuberculosis 

 sometime during their lifetime, but unless the body is unable to 

 cope with the initial infection, active disease does not develop. A 

 negative tuberculin test, therefore, has more diagnostic significance 

 than does a positive reaction. 



The use of B.C.G. vaccine, described in the previous chapter, 

 is showing promise as a means of preventing tuberculosis, but a 

 longer range study is required before conclusive statements can be 

 made about the exact effectiveness of this vaccine. Some recent 

 advances in drug therapy offer hope for those persons who are 

 suffering from active cases of this disease. 



Other diseases caused by mycobacteria include leprosy (Mt/co- 

 bacterium leprae), and johne's disease {Mycobacterium para- 

 tuberculosis), a chronic diarrhea in cattle and in sheep. 



BACILLUS ANTHRACIS 



Rod-shaped, spore-forming, non-motile, gram positive, facul- 

 tative organisms, measuring from 1.0-1.3 by 3.0—10.0 microns, 

 and having square or concave ends. Occur in long chains. The 

 cause of anthrax in man, sheep, and swine. 



The word anthrax comes from the Greek and means boil or 

 carbuncle, which is the typical tvpe of lesion seen when man 

 acquires a skin infection with Bacillus anthracis. A malignant 

 pustule forms and develops a black crust which covers a focus of 

 infection that is teeming with organisms. The infection may re- 

 main localized or it may become generalized. When growing in 

 the body the anthrax bacillus produces no spores but capsules are 

 developed. No exotoxin has been demonstrated. It has been 



