156 Bulletin 225. 



5. How TO Detect Tuberculosis in Cattle. 



From what has been said about the course of the disease, it is 

 perfectly clear that there nia}^ be a large number of animals in a herd 

 that are infected with tuberculosis but which appear to be sound. 

 There may be others in which the disease is far advanced and the 

 animals show that they are affected. There are two ways by which 

 the disease can be detected, namely, by a physical examination and 

 with tuberculin. 



The physical examination is of value in advanced cases only, or 

 where the diseased part is in evidence, as for example in the lymphatic 

 glands of the neck. Experience has shown that by this method one is 

 unable to find more than a very small percentage of the animals that 

 are tuberculous and a menace to the healthy cattle. This method, 

 therefore, is a very crude one and cannot be trusted except in the very 

 advanced cases and in those where the early stages of the disease are 

 in evidence externally. 



The tuberculin test is far more reliable. There have been many 

 unjust things said about tuberculin and many cattle owners have 

 come to fear that it is a dangerous agent to use. It has been found, 

 however, that tuberculin is as harmless as need be to the health of the 

 animal. The dangers that are supposed to come from it are the 

 results of poor tuberculin, unclean instruments, or other avoidable 

 causes. 



Tuberculin is the liquid, usually glycerinated bouillon, on which the 

 tubercle bacilli have multiplied or grown. It is concentrated after 

 heating and removing the bacteria and a little carbolic acid or thymol 

 is added to preserve it. The active principle of tuberculin is a sub- 

 stance resulting from the multiplication of the tubercle bacilli in the 

 liquid. In its preparation it is necessary that the tubercle bacilli 

 "grow" sufficiently, which usually requires several weeks before the 

 liquid is used. The flasks containing " cultures, " as they are called, 

 are, when ready, heated for some time at the boiling point. The 

 liquid is then filtered to remove the bacilli, the fluid is then concen- 

 trated over a water bath. It is again filtered through a porcelain 

 filter and stored. It will be noticed, that tuberculin is heated at two 

 different times during its preparation sufficiently to kill the tubercle 

 bacilli and it is also filtered through a substance that would remove 

 the tubercle bacilli, if any escaped the first filtration. When ready 

 for use tuberculin is a clear, amber-colored liquid. The inten- 

 sity of its color varies according to the amount of blood pigment in 

 the meat from which the bouillon was made. 



