INFECTIOUS DISEASES OF CATTLE. 411 



becomes essential. * * * In skilled hands the tuberculin test will show at 

 least nine-tenths of all cases of tuberculosis when other methods of diagnosis 

 will not detect one-tenth. 



It is perfectly natural that there should be objection to its use 

 among those who are not acquainted with its method of preparation 

 or its properties, but it is difficult to explain the antagonism of farmers 

 who are familiar with the facts connected with the manufacture and 

 use of tuberculin. Probably the most popular objection to tuberculin 

 is that it is too searching, since it discovers cases in which the lesions 

 are small and obscure. While this fact is admitted, it should also be 

 borne in mind that such a small lesion to-day may break down and 

 become widely disseminated in a relatively short period. Therefore 

 any cow affected with tuberculosis even to a slight degree must be 

 considered as dangerous not only to the other animals in the herd 

 but also to the consumer of her products. 



In 1898, Bang, of Copenhagen, one of the highest European author- 

 ities, in his paper presented to the Congress for the Study of Human 

 and Animal Tuberculosis, at Paris, said : 



Numerous tests made in almost every civilized country have demonstrated that 

 in the majority of cases tuberculin is an excellent means for diagnosing the exist- 

 ence or the nonexistence of the disease, but giving us no positive information as 

 to the extent to which the disease has progressed. When tuberculin produces a 

 typical reaction we may be almost sure that there exists in the body of the animal 

 a tubercular process. The cases in which a careful examiner has not succeeded in 

 finding it are very rare, and I am led to believe that when, notwithstanding all 

 the pains taken, it has escaped discovery, the reason is that it is located in a por- 

 tion of the body that is particularly inaccessible. Nevertheless, it is not to be 

 denied that a fever, entirely accidental and of short duration, may in some rare 

 cases have simulated a reaction. However this may be, the error committed in 

 wrongly condemning an occasional animal for tuberculosis is of no practical 

 consequence. 



A worse aspect of the case is that there are some diseased animals in which 

 tuberculin fails to discover the existence of tuberculosis. In most of these, no 

 doubt, the deposits are old, insignificant, and generally calcified, or they are cases 

 where the disease is arrested and perhaps in process of recovery, and which are 

 possibly incapable of disseminating the contagion. But it is known that there are 

 cases, not altogether rare, where tuberculin fails to cause a reaction in a highly 

 tuberculous animal, and consequently one in which the disease exists in an 

 extremely contagious form. For this reason a clinical examination should always 

 be made of an animal which does not give a reaction, but which shows symptoms 

 indicating that notwithstanding the test it may suffer from tuberculosis. 



Nocard, of Paris, wrote also in 1898 as follows: 



The degree of certainty of the indications furnished may be stated in precise 

 terms. The observation of a clear reaction to tuberculin is unequivocal; the ani- 

 mal is tuberculous. The pretended errors imputed to the method are explained 

 by the extreme sensitiveness of the reagent, which is capable of detecting the 

 smallest lesion. It often requires prolonged and minute researches in the depths 

 of all the tissues to discover the few miliary centers, the presence of which has 



