No. 6. DEPARTMENT OF AGRICULTURE. 143 



weight or yield of milk in proportion to the quantity and quality of 

 food consumed. It ap[)ears, then, that there is reason to believe 

 that some cattle have a specific resistance to tuberculosis. We 

 know that specific resistance or immunity of the individual, occurring 

 under natural conditions, usually depends on a previous attack of 

 the disease against which the animal is immune, or, as m the case of 

 Texas fever, upoo the continued existence of the disease in a form so 

 mild as not to appreciably disturb the various functions. This prin- 

 ciple receives practical application when persons are rendered im- 

 mune to small-pox or animals to anthrax, black-quarter, lung plague, 

 rabies, or Texas fever by inoculating them with the attenuated but 

 living virus of the respective disease, and thus causing them to de- 

 velop it in a comparatively mild form, from which speedy recovery 

 a4id subsequent immunity are almost certain. 



From the inoculation there results the automatic development of 

 an antitoxin that counteracts the toxin of the disease, and, at the 

 same time, prevents or retards the growth of the organism of that 

 disease. Until comparatively recently this principle has been thought 

 to hold only in respect to certain acute infectious diseases, but it is 

 now known to be of much wider application. Protection upon this 

 principle is usually known as vaccination. In some cases the germ- 

 free toxin IS used for a similar purpose. 



In 1901 we conducted an experiment for the purpose of determin- 

 ing the influence of Koch's original tuberculin upon the resistance 

 of cattle to tuberculosis. In this experiment were used four cows 

 known by the numbers 2G5o4, 26555, 2055G, and 26557. Each was 

 tested with tuberculin before it was admitted into the experiment. 

 Two of these cows, 26554 and 26557, were given daily injections of 5 

 c. c. of concentrated tuberculin for ten days, from August 24 to Sep- 

 tember 2, 1901, inclusive. Each of the four cows in the experiment 

 was fed daily 100 grammes of hacked tuberculous lung tissue from a 

 cow, for ten days, from the 10th to the 19th of iSeptember, inclusive. 

 The first pair of cows. 26554 and 26557, that had received preliminary 

 injections of tuberculin were given subcutaneously 15 c. c. of concen- 

 trated tuberculin each day during the progress of the feeding upon 

 tuberculous material. The other two cows, 26555 and 26556, which 

 had not received the daily preliminary injections of tuberculin, re- 

 ceived no tuberculin during the experiment. 



One of the cows (26554) that bad been treated with tuberculin, 

 and one (26555) that had not been treated with tuberculin were 

 killed November 25, 1901. The cow (26554) that had been treated 

 with tuberculin showed upon post-mortem examination lesions of 

 tuberculosis in the postpharyngeal and mesenteric lymphatic glands. 

 The control cow (26555) showed lesions of tuberculosis in the right 



