TUBERCULOSIS. 421 



Numerous tests made in almost every civilized country have demonstrated 

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

 the existence or nonexistence of the disease, but giving us no positive infor- 

 mation as to the extent to which the disease has progressed. When tul>erculin 

 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 portion 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, whei*e 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 reac- 

 tion 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. TJie observation, of a clear reaction to tuberctilin is unequivocal ; the 

 animal is tuberculous. The pretended errors imputed to the method are ex- 

 plained by the extreme sensitiveness of the reagent, which is capable of detect- 

 ing 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 been revealed. The reaction is absolutely specific. In those cases 

 where it is observed with animals which show lesions of another disease (acti- 

 nomycosis, hydatid disease, verminous bronchitis, distomatosis), it may be 

 affirmed that there exists, in addition to these conspicuous changes, a tubercu- 

 lous center which alone has provoked the reaction. 



The failure to react does not necessarily imply absence of tuberculosis. Such 

 failures of tiiberculin are very exceptionaL They are seen most frequently with 

 animals affected with tuberculosis in a very advanced stage and made evident 

 by plain external signs. Sometimes, also, there are found at the post-mortem 

 examination of animals which have not reacted small fibrous or calcified lesions 

 in such a condition that one is tempted to believe them cured. Whether sterile 

 or not, these lesions have no tendency to increase, and they are not very danger- 

 ous from the point of view of contagion. 



These oj)inions of t%Yo eminent authorities, living in different 

 countries, after long experience of their own and after studying the 

 results of the many tests made in different parts of the world, should 

 have great weight. They are essentially the same throughout. 



In 1897 Voges compiled statistics of tuberculin tests, the accuracy 

 of which had been determined by post-mortem examination. Of 

 7,327 animals tested, it appeared that errors had been made with 204, 

 or 2.78 per cent. In the work of the Pennsylvania Live Stock Sani- 

 tar}^ Board post-mortem examinations were made on about 4,400 

 reacting cattle and the disease was found in all but 8 of those which 

 had given characteristic reactions. 



