122 ANNUAL. REPORT OF THE Off. Doc. 



at a minimum of loss. It is conservative to the last degree. Those 

 who have carried it out correctly have had good results. But we 

 have to take the facts as they are and to recognize that the Bang 

 system in its entirety is not likely to be used extensively in this 

 country. 



''The other methods that have been proposed for the repression 

 of tuberculosis are much more expensive because they involve the 

 loss of the breeding value of infected cattle and usually require 

 their destruction. While under present regulations it is possible 

 to save the beef value of some infected cattle, this is of little im- 

 portance in regard to most dairy herds. 



''It has long been evident that if some more economical method 

 for the control of tuberculosis could be devised and placed in opera- 

 tion it would have a marked effect on the development of improved 

 breeds and on the gradual betterment of the average herds, through 

 the use of better blood. 



"Many men refrain from paying high prices for cattle and from 

 maintaining pure bred herds on account of the prevalence of tuber- 

 culosis. Many breeders, of nearly all breeds, have given up breeding, 

 and some have been ruined on account of the ravages of tuberculo- 

 sis. It is not pleasant to dwell on this subject but we must be brave 

 enough to look squarely at the question, and to attempt to measure 

 it. And if a satisfactory remedy can be found even a grave ill need 

 not terrify us. 



"The studies that have led up to a development of a process for 

 vaccinating cattle against tuberculosis have covered many years. It 

 was in an effort to isolate a substance to increase resistance to tu- 

 berculosis that Koch discovered tuberculin in 1880. This material 

 does not possess the properties that were at first ascribed to it but 

 it is of the greatest vaule as a diagnostic and is of considerable val- 

 ue in treating tuberculosis of man as is shown by the constantly in- 

 creasing dependence that is being placed on it. 



"Following this discovery, a great many extracts and preparations 

 of tubercle bacilli and their cultures were prepared but none was 

 sufficient to increase the resistance of an auimal to a useful degree 

 until living tubercle bacilli were employed, non-virulent for the ani- 

 mal treated. This use of the living germs of a disease for the pur- 

 pose of securing protection from the disease caused by more virulent 

 germs of the same species was first employed by Jenner in relation 

 to smallpox. The germs of smallpox when grown on cattle are 

 thereby so changed that they become incapable, when inoculated 

 upon man, of producing smallpox but they do cause a small erup- 

 tion at the point of the inoculation and following this the vaccinated 

 person becomes immune to smallpox. This principle was employed 

 and its application was extended by Pasteur in relation to the dis- 

 eases, fowl cholera, anthrax and rabies. It has also been applied suc- 

 cessful in respect to blackquarter, swine erysipelas and other mal- 

 adies. 



"Among the first attempts to apply this principle to tuberculosis 

 were those of Dixon, Trudeau and deSchweinitz, all in this country. 

 But the scientific groundwork for the development of this method 

 was laid in 1896 and 1898 by Theobald Smith who discovered that 

 although tuberculosis is widely distributed through the mammalian 



