DISEASES COMMUNICABLE IN MILK 39 



found in the herd milk produced by cows passed as free from udder tuber- 

 culosis by skillful veterinarians especially on the lookout for evidences 

 of the condition. 



How the physical examination in this country works out is exempli- 

 fied by the experience of Montclair, N. J. (see Table 25, p. 49). For 8 

 years prior to the enforcement of the requirement that milk should either 

 come from tuberculin- tested cows or be pasteurized, the herds supply- 

 ing the town were subjected annually to a physical examination by veteri- 

 narians paid by the dairymen. When the tuberculin test was applied 

 to 15 of these herds all but one contained tuberculous animals, about 

 25 per cent, of the animals being reactors. It is stated that at the time 

 of testing, in only a few cases could the disease have been discovered by 

 physical examination. As autopsies were not performed on the reactors, 

 it is not known how many of the herds had animals with open tuberculosis. 

 To be at all effective, physical examinations must be both frequent and 

 thorough; consequently some dairymen object on the score of cost, 

 and it is probably true that in the United States adequate physical 

 examinations would be more expensive than tuberculin testing. 



Tuberculin. Tuberculin, discovered by Koch, in 1890, has been used 

 as a diagnostic agent for tuberculosis in cattle since 1891 and has been 

 adopted everywhere for this purpose. It is a liquid, usually a glycerinated 

 broth, that contains products thrown off by tubercle bacilli grown in it. 

 These products cause the temperature reaction that identifies a tubercular 

 animal that has been injected \\ith tuberculin. There are no tubercle 

 bacilli in tuberculin because in the process of preparation they are killed 

 by heat and removed by filtration. 



According to Moore the technique of preparing tuberculin is as follows : 



"The tubercle bacteria are grown in pure culture at about 99.5F. on a liquid 

 medium consisting of beef tea containing peptone (about 1 per cent.) and glycerin 

 (from 5 to 7 per cent.). In some laboratories a little acid potassium phosphate 

 is added. This glycerinated, peptonized broth is put in flasks, usually in from 

 100 to 250-c.c. amounts. After it is sterilized it is inoculated with tubercle bac- 

 teria by transferring some of the growth from a young culture to the surface of 

 the liquid in the flask. The bacteria do not grow in the depth of the liquid but 

 form a membrane over the surface. After the cultures have grown long enough, 

 from 4 to 10 weeks, the flasks are placed in a water bath and heated to from 121 

 to 149F. for about 2 hr., after which they are boiled. After boiling, these cul- 

 tures are filtered through ordinary filter paper to remove the mass of bacteria. 

 The filtrate is then evaporated over a water bath to the desired consistency and 

 is then filtered through a porcelain Berkefeld filter. In some laboratories it is 

 filtered through the porcelain filter before it is concentrated. 



"The original Koch tuberculin was evaporated to one-tenth the volume of 

 the culture liquid, that is, 100 c.c. of the culture was evaporated to 10 c.c. and a 

 little carbolic acid (one-half of 1 per cent.) added to the filtrate to preserve it. 

 It is kept in glass-stoppered bottles. 



