THE PROTECTION OF THE HERD. 273 
of the rest of the herd. Experience has shown that, of the animals 
responding to the test, some run down rapidly and require slaughter- 
ing in a few weeks, while others wholly recover, live several years 
of useful life, and after death show, by postmortem examinations, 
that the original tubercle has been healed and the animals have 
come again into normal condition. There is thus a great difference 
between clinical tuberculosis and tuberculin tuberculosis. The former 
results practically always in the death of the animal, the latter may 
be temporary and insignificant. The former certainly is, and the 
latter may or may not be, a source of danger to the herd. 
In the enthusiasm which followed this easy means of detection, 
it was claimed that it might be possible to eradicate tuberculosis 
completely from our herds, and some States started upon a sweeping 
plan of testing all cattle and slaughtering immediately all animals 
that responded to the test. But this entirely too radical plan 
proved quite impracticable. Nevertheless, the use of tuberculin has 
become of great value to the farmer in his attempts to get rid of this 
disease among his cattle. 
The Preservation of a Healthy Herd. If a farmer has a herd 
in which the disease has not appeared, it is of especial interest to him 
to keep his herd in this condition; for, once the disease has entered 
the herd, it is very difficult and expensive to stamp it out. Tuber- 
culosis does not develop spontaneously in a herd of animals, but 
is always introduced from the outside. A farmer who can raise his 
own cattle and can properly protect them from contact with out- 
siders need have no tuberculosis among them. But to protect the 
herd requires some knowledge and great vigilance. To prevent 
the entrance of the disease into his herd from without, the farmer 
must exercise care in several directions. 
First: In buying stock he must be sure not to purchase in- 
fected animals. This is perhaps the greatest difficulty, for it is most 
commonly by purchase that the disease is introduced into a herd. 
There is only one way by which he may be sure that he is not 
purchasing infected cattle, and this is by a proper tuberculin test, 
under the guidance of a reliable veterinarian. The matter is made 
more difficult by the fact that after an animal has been tested and 
