172 TUBERCULOSIS 
Haring recommends at least a 5% solution of alcoholic precipitated 
tuberculin in normal salt solution. He injects from 0.1 to 0.2 ce. 
Koch’s Old Tuberculin in 10% solution has also given good results. 
A number of chemical firms put out intradermal tuberculin but they 
do not seem to be uniform in their preparation. Hutyra and Marek 
state that a 50% solution of Koch’s Old Tuberculin gave good results. 
Some in this country use the Bureau of Animal Industry tuberculin 
direct in doses of from three to five drops and do not believe it is neces- 
sary to use the purified or precipitated tuberculin. 
A positive reaction from the intradermal use of tuberculin is indi- 
cated by a thickening of the subcaudal fold or by the appearance at the 
point of injection of a characteristic sensitive swelling varying in size 
from that of a small pea to that of an orange. The swelling may be 
either edematous or hard and inflamed. The swelling can be recog- 
nized in some cases by the sixth hour. Generally it is not clear until 
about the twelfth hour. The swelling continues to increase in size 
for two or three days. In some cases the swelling does not appear so 
early. If only one observation can be made after the injection, it is 
recommended by Haring that it should be on the 72d hour. He 
states: “Small indurations at the point of inoculation about the size 
of the head of a parlor match frequently occur in normal non-reacting 
cattle, but anything larger than this which persists to the seventy- 
second hour should be considered a positive reaction.” 
In recording the reactions, a convenient method for comparison is 
to describe the size of the swelling as pea size, hazelnut, walnut or 
hen’s egg size. The exact size, if desired, may be measured by means 
of calipers. Romer and Joseph consider that a thickening of the skin 
fold more than three millimeters larger than the thickness previous to 
injection should be considered a positive reaction. Cases in which 
the increase in thickness amounts to only three millimeters, they 
consider doubtful and subject to a retest. In our work, however, we 
have found the measurement of the swelling was not of much assist- 
ance. Experience and practice will enable the operator to judge of 
the size of the swellings without measuring, although for the sake of 
accurate records we have made a practice of taking careful measure- 
ments. . 
“In judging a local swelling, the observer should depend more upon 
the shape, appearance, tenseness, sensitiveness and location with 
respect to the exact point of injection, than upon the actual measure- 
ments. Only experience can teach an operator how to be certain of 
