E. A. Watson 
157 
Introduction. 
This paper is written with the purpose of drawing further attention 
to the value of the complement fixation reaction as a diagnostic test in 
dourine and of recommending a method of procedure and technique 
arrived at with an experience of 15,000 tests for dourine made at the 
Veterinary Research Laboratory, Lethbridge. 
In a previous paper I have briefly described the serum reactions in 
dourine. Since that paper was published in 1912 (Proceedings of the 
Amer. Vet.-Med. Assoc.) diagnostic tests for dourine have been carried 
along continuously at this laboratory, together with exhaustive control 
and experimental tests and the searching out of every possible source 
of error. By the numbers of horses available for experiment, the pro¬ 
longed trial of the test through every known phase of the disease and 
its widest application in naturally occurring outbreaks, coupled with 
observations in company with the veterinary officers in charge of the 
field work, the complement fixation reaction has been thoroughly 
established as a sure, safe and specific method of diagnosing dourine. 
The experience shows that the test meets every requirement with regard 
to specificity, uniformity and decisiveness. It has been adopted as 
the official test for dourine in this country by Dr F. Torrance, Veterinary 
Director General for Canada, who kindly permits me to publish this 
paper. 
By the complement fixation test it has been possible—and without 
difficulty—not only to make a certain diagnosis of the more or less 
symptomatic cases, but, and of greater importance, to positively 
determine the existence of the non-clinical, obscure and latent forms of 
infection. 
Only by a systematic application of the test to every animal exposed 
to infection—and in no other way known at present—can the healthy- 
looking, so-called immune carriers of dourine be detected. When it 
is remembered that horses may tolerate a dourine infection for periods 
of one to three years and remain for that time normal in general health 
and appearance but capable at times of transmitting the disease, the 
necessity of an early and definite diagnosis is evident. The complement 
fixation test furnishes this and thus becomes of great importance as a 
basis for the control and suppression of dourine. It is being applied 
in every known outbreak of dourine in Canada, and, as a precautionary 
measure, in the various studs and to stallions standing for service in 
the districts that have come to be considered as dourine-infected areas. 
