io6 
Journal of Agricultural Research 
Vol. I, No. a 
The hemolytic system consists of sensitized rabbit serum, serum from 
a guinea pig, and a 5 per cent suspension of washed sheep corpuscles. 
The serum to be tested is, of course, inactivated for one-half hour at 
56° C. and is used in the tests in quantities of 0.15 c. c., since it has been 
found that fixation in this quantity is obtained only with sera of horses 
affected with dourine. Tests to determine the smallest quantity of serum 
of horses having dourine which will give a fixation showed that in 
several instances even 0.02 c. c. of serum was sufficient to give a com¬ 
plete fixation. 
The complement from the guinea pig is always titered previous to the 
test, as it is absolutely necessary to use the exact amount of the comple¬ 
ment to obtain the best results, since a deficiency or an excess of the com¬ 
plement would interfere greatly with the reaction. 
In the numerous cases which have been tested the results were almost 
invariably definite, and only on a very few occasions was it found neces¬ 
sary to make retests on cases which appeared atypical. The reaction is 
always very marked, and in our work only a complement fixation with 
the quantity of serum mentioned is recognized as a positive reaction. 
It is only proper that in the tests the usual number of checks should be 
employed in order to insure reliable results. 
Since the testing has been undertaken by the method described, 
8,657 samples have been examined from Montana and the Cheyenne and 
Standing Rock Indian Reservations in North Dakota and South Dakota. 
Of these, 1,076 gave positive reactions, which appears to be a very large 
proportion, but when it is remembered that these animals were kept 
under range conditions without sanitary or veterinary control and also 
that before the disease was recognized as dourine it had been diagnosed 
for a long period as some other affection, it will be apparent that the 
opportunity for the spread of the disease was ideal. 
With the present system of diagnosis, by which even the latent cases 
can be determined, it is hoped to eradicate the disease quickly. All the 
horses in the infected localities will be submitted to the complement- 
fixation test, and by cooperation with the State authorities means will 
be devised to dispose of the affected animals in such a way as to make 
the further spread of the disease impossible. The animals which were 
destroyed as a result of the disease in the above-named localities and 
which were diagnosed by the complement-fixation test showed in most 
instances some lesions indicative of the disease. In some of the cases 
there were no indications of a progressive paralysis, but the lesions 
existing in the genital organs of either the male or female were sufficient 
for confirmation of the diagnosis by the complement-fixation test. 
It is therefore evident that the diagnosis of trypanosome infections 
of both man and animal by the complement-fixation test is of very great 
importance, especially in countries where only one of these protozoan 
