E. A. Watson 
175 
Experiment for determining the length of time between dourine infection 
and the first appearance of a positive serum reaction. 
A healthy filly, 2J years old, was infected with dourine by smearing 
over the vaginal mucosa a few drops of blood containing Trypanosoma 
equiperdum. 
Serum was collected from this young mare before infection and 
daily up to the fifteenth day after infection, and tested by the comple¬ 
ment fixation method, with trypanosome antigen. The results were 
as follows: 
Dose of Before Days after infection 
serum infection -*- 
c.c. 
1 to 10 
n 
12 
13 
ii 
15 
r 0-2 
- 
- 
+ + + 
+ + + + 
+ + + + 
+ + + + 
+ + + + 
015 
- 
- 
+ + 
+ + + + 
+ + + + 
+ + + + 
+ + + + 
lo-i 
- 
- 
+ 
+ + + 
+ + + + 
+ + + + 
+ + + + 
0-05 
- 
- 
- 
+ + 
+ + 
+ + + + 
+ + + + 
001 
- 
- 
- 
- 
- 
+ 
+ + 
0-005 
— 
- 
- 
- 
- 
- 
+ 
Thus, 
the first 
appearance of 
a positive 
serum 
reaction was 
eleven 
days after infection. 
In three earlier experiments of this kind, but in which serum was 
not collected for testing until the twentieth day after infection, the 
reaction in each case was strongly positive. 
The incubation period of dourine in the light of the complement 
fixation test is indicated, by the above experiments, as not less than 
eleven days and not over twenty days. However, the strain of dourine 
used in these experiments was of high virulence; when horses become 
infected with strains of low virulence—and there is much variation in 
dourine strains—the incubation period is probably prolonged. 
A negative reaction should not be taken as final or conclusive when 
the interval between exposure to infection and the collection of test 
serum is less than two months. 
IV. The Diagnostic Test. 
Two methods of procedure are here recommended: 
(1) When only one or several tests are to be made. 
(2) For daily routine testing or when 50, 100, or more tests are to 
be made at one time. 
