472 IOWA DEPARTMENT OF AGRICULTURE 
"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 con- 
tagious form. For this reason a clinical examination should always be 
made of an animal which does not give a reaction, but which shows symp- 
toms indicating that notwithstanding the test it may suffer from tuber- 
culosis." 
Nocard, of Paris, wrote also in 1898 as follows: 
The degree of certainty of the indications furnished m.ay be stated in 
precise terms. The observation of a clear reaction to tuberculin is un- 
equivocal; the animal 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 pro- 
longed 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 (actinomycosis, hydatid 
disease, verminous bronchitis, distomatosis), it may be affirmed that 
there exists, in addition to these conspicuous changes, a tuberculous cen- 
ter which alone has provoked the reaction. 
"The failure to react does not necessarily imply absence of tubercu- 
losis. Such failures of tuberculin are very exceptional. They are seen 
most frequently with animals affected with tuberculosis in a very ad- 
vanced 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 dangerous from the 
point of view of contagion." 
These opinions of two 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 has been determined by post-mortem examination. Of 7,327 ani- 
mals tested it appeared that errors had been made with 204, or 2.78 per 
cent. In the work of the Pennsylvania Live Stock Sanitary Board post- 
mortem examinations were made on about 4,400 reacting cattle and the 
disease was found in all but eight of those which had given characteristic 
reactions. 
The results of a much larger number of tests might be compiled at 
this time but they would not materially change the average of those al- 
ready mentioned. It is plain that tuberculin is a remarkably accurate 
test of tuberculosis; that the animals which react may be safely con- 
