VERMONT AGRICULTURAL REPORT. 139 



tuberculous animals do not show an appreciably higher reaction 

 with large doses of tuberculin than with medium doses ; hence, 

 while the above methods of standardization are not so accurate 

 as those which would have to be used in weighing out a very 

 poisonous alkaloid, experience has shown that they are suffi- 

 ciently accurate for ordinary work. 



If the tuberculin is intended for use upon man, it should, 

 in addition to the filtration through a fine filter paper, be filtered 

 through porous porcelain, so as to remove the last possible 

 germ. In the preparation of tuberculin, however, for use upon 

 animals, especially when attenuated cultures are used as the 

 source for the material, this filtration through porcelain is not 

 necessary. 



LOSS IN PREPARING AND COST OF TUBERCULIN. 



In handling large amounts of culture media for the prepar- 

 ation of tuberculin there is always a certain amount of unavoid- 

 able loss. Sometimes in the process of inoculation, even with 

 the utmost care, the flasks will become contaminated by some 

 foreign germ. Sometimes the contamination may not take 

 place until the culture is pretty well grown. Then it is often 

 due to an imperfect plug or unavoidable handling of the culture. 

 The quantity of cultures lost depends, of course, upon the care 

 of the individual in handling them, the care in inoculation, and 

 the locality in which this work is conducted. All inoculations 

 of tubercle flasks, as well as other culture media, should be 

 made in an air that is free from dust, and consequently free from 

 dangers of contamination. When proper care is used, possibly 

 one-fourth of i per cent, of the flasks are lost, but the writer 

 has found that in the hands of inexperienced individuals 20, 

 30, and even 50 per cent, of culture flasks maybe contaminated. 

 Frequently, as in the case of tubercle cultures, this contamina- 

 tion can be very readily detected. So long as the cultures are 

 pure the germs will be found floating upon the surface of the 

 liquid or at the bottom of the flask, while the rest of the media 

 will be perfectly clear. The slightest contamination causes the 

 media to become cloudy ; and as soon as this is noted the flasks 

 should be discarded, as tuberculin should be prepared only 

 from perfectly pure cultures. In experienced hands the cost of 

 the preparation of tuberculin is not great. It should be made 

 and sold, giving a fair profit for the trouble connected with its 

 manufacture, at not over five cents a dose. 



THE METHOD OE USING TUBERCULIN. 



The regulations prescribed for many years by the Bureau 

 of Animal Industry for the use of tuberculin in testing cattle are 

 as follows : 



