12 



culosis at the same time. In such cases small tuberculous deposits 

 may easily escape notice. 2" 



Although the negative autopsy results, in the case of reacting ani- 

 mals, may be doubled, it is true that tuberculosis is frequently found 

 in an animal which has not reacted. Very often one finds such ani- 

 mals far advanced in disease, but ofteuer yet with very insignificant 

 calcified deposits^ ^ (especially in the lymph glands) frequently so 

 old and so completely impregnated with lime that one involuntarily 

 inclines to believe a cure has taken place. 



The absence of reaction in those forms of tuberculosis has certainly 

 very slight significance in the practical application of tuberculin. It 

 must be acltnowledged that in the division of a tested herd, it would 

 be possible to include in the healthy division a few^ animals with 

 tuberculosis in the form of small lime impregnated knots in a lymph 

 gland. Such animals, however, are not infectious at that period, and 

 probably would never become so. But if the disease should develop 

 in an unsuspected manner, the animals would in all probability react 

 with a repetition of the test in the following year. 



Much more difficult are those eases in which there is an absence of 

 reaction in far advanced tuberculous animals. But in such it will 

 probably always be possible to discover the disease by the usual 

 clinical investigation. 



It has often been proved that repetition after a short time can call 

 forth an indifference so that only a weak reaction, or no reaction 

 appears. 



Apparently a single tuberculin reaction can suppress for a year's 

 time the susceptibility of an animal for this reagent. The reacting 

 division at Thurel)ylille, I have tested annually since the beginning of 

 the experiment in the year 1892. To my surprise, I found at the time 

 of testing in '93 that the reaction was absent in about 20 per cent of 

 the animals. In order to ascertain whether this was caused perhaps 

 by the cure of the tuberculosis, four of the animals were butchered 

 and very closely studied. They all had tuberculosis. In three it 

 was very sliglit and of long standing.-*'^ The fourth was tuberculous 



20. Here belong the observations, conininnicuted by me, in XXI. Vol. page 43S of 

 tliis .Journal. — Johne. 



•21. Among the animals which were separated from the healthy division at 

 Thiirebylille, I l)ave seven such ca.ses. The.se iininials were tested from two to six 

 times at intervals of six months without having reacted. In the po.st mortem 

 exainiiiatit)n of ol<l cows which we had injected in order to control the diagnostic 

 power of tuberculin before its shipment, INIr. Stribolt has often made the same 

 observation. 



40. a. (2 1-2 years old) reacted to 40.3° May 1S92, while the temperature in two 

 tests in May and July 1893 did not exceed 3'J°. The dissection in Aug. 1893 showed 



