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been ascertained,—far more so, in fact, than that of a mallein or 
tuberculin reaction which, in application and interpretation, is crude in 
comparison. The very delicacy of the fixation reaction and the strict 
laws and conditions governing it, add to the exactness, value and 
reliability of the test. 
Is the technique too intricate and laborious ? Not more so than many 
other necessary and accepted laboratory methods, and this is essentially 
a laboratory test. 
Is it necessary to use a pure suspension of trypanosomes as antigen ? 
By the employment of a pure suspension of dourine trypanosomes as 
antigen non-specific and false or misleading reactions are avoided. 
Many other ways of preparing antigen for the dourine test have been 
tried by different investigators but, with one exception, with little 
success. Mohler and Eichhorn recommend a spleen preparation of a 
rat dead from surra. I have used the spleens of rats dead from dourine 
in several thousand tests and with very good results, but, on the whole, 
such preparations are inferior to the trypanosome suspension and possess 
a number of disadvantages. Spleen preparations are often troublesome 
on account of a more or less anticomplementary action or owing to a 
weakness in specific antigenic property. They are very unstable and 
of inconstant value and give rise to many borderline or questionable 
reactions which can be eliminated or definitely decided by the try¬ 
panosome antigen. In comparative titrations of dourine sera with the 
two forms of antigen I have found that approximately one-tenth of the 
amount of serum necessary for a positive reaction with spleen antigen 
suffices for a clear positive reaction with trypanosome antigen. Very 
weak positive reactions-with the former become clearly and strongly 
positive with the latter, which, therefore, should always be given the 
preference. The trypanosome suspension has also the great advantage 
of retaining a constant value for several weeks at least, for six to eight 
weeks if carefully prepared, and thus allows of the keeping of a uniform 
stock antigen. 
What is the percentage of positive reactors in dourine outbreaks ? This 
of course varies according to the length of time the disease has been in 
existence in a stud or range herd before being checked by preventive 
measures. In the most extensive oubreak that we have had to deal 
with 456 positive reactors were found in a total of 2000 animals tested; 
nearly 23 per cent. In an outbreak on an Indian Reservation, 127 
animals gave positive reactions out of 1464 tested, or less than 9 per 
cent. Usually it is between 15 and 20 per cent. Our experience 
Parasitology vm 
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