272 AGRICULTUEAL BACTERIOLOGY 



because these animals are more susceptible than grades, but 

 because the opportunity for infection in pure bred herds 

 lias been much greater because of the interchange through 

 purchase. For the same reason, large herds are more likely 

 to be tubercular than small herds. The disease is one that 

 spreads by direct contact among cattle kept out of doors 

 almost as rapidly as in the case of those that are stabled 

 for a large part of the year. 



Different names are applied to the various manifesta- 

 tions of the disease in man. Consumption and phthisis 

 refer to tuberculosis of the lungs ; scrofula to tuberculosis 

 of the glands of the neck ; lupus to that of the skin ; and 

 joint disease to that of the joints. In cattle, grapes and 

 pearl disease, terms sometimes used by butchers, refer to 

 tuberculosis of the serous membranes. 



The tubercle bacillus. The tubercle bacillus is a slender 

 rod that is a member of the acid-fast group, which includes 

 the organism causing leprosy and that producing Jolme's 

 disease in cattle, and also a number of non-pathogenic ba- 

 cilli, which are found in manure and on plants. The term 

 acid-fast refers to the fact that the organism, when stained, 

 retains the dye when treated with dilute solutions of min- 

 eral acids, while other bacteria are decolorized at once. 

 This property of the tubercle bacillus is used for its detec- 

 tion in sputum, milk, and tissues. 



The tubercle bacillus does not produce spores. It is, 

 however, resistant to desiccation and other physical and 

 chemical factors, a fact of importance in the spread of the 

 disease. It grows very slowly on all kinds of culture media, 

 and probably in the animal body, a fact of significance in 

 explaining the extended period of incubation of the disease, 

 which is from a few weeks to several months in length. In 

 cultures the tubercle bacillus grows only on the surface of 

 the medium. 



