THE INTRADERMAL TUBERCULIN TEST. 
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ratio, there is a probability of less than one error in the 35 re¬ 
acting cows still on hand. Up to the present time, the intra- 
dermal test shows a little over 98 per cent, accuracy. Granting 
that one more animal will show no lesions, making three in all, 
we shall have made three errors in testing over 3,458 head of 
cattle. This is far better than we have ever been able to do with 
the temperature test. 
In beginning our intradermal test we were a little careless, 
sometimes purposely so, in regard to surgical cleanliness. While 
it is impossible to approach surgical cleanliness in using this 
test, we soon found it paid to be as clean as possible. Very 
few swellings result from infection and they are quite different 
in character from the swelling resulting from a positive reaction. 
The former is soft and inclined to extend along the tail, and 
passes away sooner. The characteristic reaction from the intra¬ 
dermal test is slightly rounded, very hard, rather painful and 
persists for several days. As far as our experience has gone, it 
appears that the reaction from the intradermal test will, on the 
average, be at its height on the third day. Sometimes, as matter 
of convenience, a re-examination of cattle after injection may be 
made on the second or fourth day, but our rule is to make this 
examination on the third day. 
We have found that the intradermal injection should be 
made with a medium-sized needle; a very small needle might be 
preferable, but is too easily broken. It is my opinion that the 
opening in the epidermis made by a large needle gives more 
opportunity for infection. We find it convenient to administer 
this test, taking hold around the tail with the left hand, and 
seizing the bare skin on the under surface between the middle 
finger and the thumb, pulling it around as far as possible to one 
side. At first we attempted to pick up the caudal fold. We soon 
found that this was a waste of time, and in our desire to get 
along with the work, we were willing to make the injection 
wherever we could find the skin soft and pliable. It is difficult 
to describe the insertion of the needle, but herein lies the secret 
of accuracy. A thoroughly clean needle should be pushed along 
