'J 



04 AGRICULTURAL DEPRESSION 



of nearly 1,700,000 head of cattle, and that under the 

 test 387 per cent, had re-acted. Of those tested, the 

 large herds — those with 50 head or more — showed the 

 worst results. About two-thirds of these herds show 

 59 per cent, of re-acting animals, and about one-fourth 

 show over 75 per cent. In the small herds, there are 

 many found wholly exempt from disease, while more 

 than one-half have less than 25 per cent., and only a 

 tenth show 75 per cent, or more. The existence of 

 entirely healthy herds upsets the theory that the bacilli 

 of tuberculosis are everywhere present, and gives more 

 basis for the hope that the disease can be extirpated. 

 Doubt is also thrown on the hypothesis that " in and in " 

 breeding is a cause of spread of the disease, Mr Bang 

 has found two herds most of which originated from the 

 same cow, and had been increased by in-breeding, but 

 were absolutely free from taint. The importation of 

 breeding animals for the improvement of big herds has, 

 in his opinion, caused infection, which has been spread 

 from the larger to the smaller farms. 



The test has been found to be faulty in Germany 

 in I3'i4 per cent, of instances, and in Denmark in 97 

 per cent, of instances. In some of these cases dissection 

 has shown tuberculosis to exist, though there has been 

 no re-action. In other cases where there has been re- 

 action, and dissection shows apparently healthy tissues, 

 it is quite possible that minute tuberculous deposits have 

 escaped attention. " Knots from the size of a needle's 

 head to that of a pea, in a hidden lymph gland sur- 

 rounded by fatty tissue, may be overlooked even by 

 those of most experience." Thus the proportion of 

 cases in which the test is a fairly certain indication is 

 probably greater even than 86 to 90 per cent. In the 

 great -majority of cases, the reaction merely indicates 

 latent tuberculosis, and the test gives no guide as to the 

 degree to which the disease has advanced, incipient 

 tuberculosis giving sharper re-action than old standing 

 cases. Again, there is serious difficulty from the 

 different degrees of susceptibility of different animals 

 and different stages of the disease. On a repetition of 



