DAIRY MEETTXG. IO3 



propagations through dust agree no matter what the source 

 from which it was obtained. 



Late in November, 1890, Koch first pubhshed the results of 

 experimental work upon tuberculous guinea pigs with a fluid 

 of his own preparation. This fluid, which he called tuberculin, 

 was stated at a later date to be highly concentrated, sterilized 

 and filtered liquids in which pure cultures of the "bacillus- 

 tuberculosis" had been grown; a pure culture consisting of the 

 growth of one species of germ by itself, all others being ex- 

 cluded. 



Tuberculin is prepared by growing the tubercle-bacilli in a 

 pure culture until a large amount of ptomains is developed. 

 Glycerine and carbolic acid are then added, and the mixture 

 is filtered to remove germs. The filtered product is then heated 

 to 225 degrees F. to destroy the vitality of any germs which 

 may have passed the filtering process, and then evaporated at a 

 low temperature until concentrated. Koch's newest method is 

 an apparatus for crushing the bacilli ; by its means micro- 

 organisms are crushed and destroyed, while the spores and 

 toxines that escape are largely destroyed by sterilization. 



The test upon cattle is made as most of you know, by inject- 

 ing the fluid under the skin of the neck or shoulder by means 

 of a sterilized hypodermic syringe, two cubic-centimeters of a 

 ten per cent solution being used. The normal temperature of 

 the cows may vary from 100 degrees to 102 degrees and is taken 

 before or at the time of injection, and tuberculous animals 

 respond by a rise in temperature, usually beginning from eight 

 to ten hours after injection and continuing as late as the twen- 

 ty-fourth hour. The great objection to the action of tuberculin 

 in the human patient is that it acts as am excitant, arousing 

 germs to increased activity and tending to scatter the infection 

 throughout the body, as shown by a rise of temperature of from 

 2 degrees to 8 degrees F., but the very features which pro- 

 hibit its use as a cure, are those which have given it its great 

 value and popularity as a diagnostic agent in determining the 

 disease in cattle. When tuberculin is introduced into the body 

 of an animal in the slightest degree affected by tuberculosis, the 

 tolerance of the system which had been gradually acquired, is 

 overcome, and the toxic effect is manifested in what is termed 

 a reaction ; while as proof of i,ts harmless effects upon well ani- 

 mals, among the first tests made in New England were those 



