180 
Dourine 
(3) The use of twice the amount of antigen which with a dourine 
antibody unit is necessary to fix the complement, provided the same 
amount of antigen alone has no inhibitory action. 
(4) Careful control of the inactivation of suspected sera by known 
positive and known negative sera. 
(5) Control of the diagnostic tests by a series of known positive 
sera, each having an antibody unit of different value, high to low. 
Discussion. 
The reliability of the complement fixation test as a certain and 
specific means of diagnosis has been questioned, not, I think, very 
seriously or on strictly scientific grounds, but more in respect to its 
practical application and on au unwarranted supposition that it is 
still very imperfectly understood, that the technique and method of 
procedure is so intricate and laborious, that the reactions themselves 
are subject to and have to be guarded against so many possible disturbing 
influences that the adoption of such a method of diagnosis is attended 
with considerable risk. 
Can the test he practically applied ? Yes, without doubt, and with 
as much ease as a mallein or tuberculin test is applied. In the one case 
blood is collected in the field and sent in for a laboratory test, in the 
other the reagents are prepared in the laboratory and sent out for a 
field test. Further, as many retests can be made by the complement 
fixation method as desired, for no toxins or immunizing substances 
are injected into the suspected animal to interfere with subsequent 
diagnostic tests. This test is no longer a new departure in veterinary 
diagnoses; it is successfully applied in glanders, contagious abortion 
and in other specific diseases and is yearly coming into more general 
use. 
Are the test reactions and the different factors concerned in them imper¬ 
fectly understood ? Such a view is not held by serologists and can only 
be retained by those who have not the opportunity of closely studying 
the subject and becoming familiar with the finer points of it. Any 
attempt to apply the test by one who has not thoroughly mastered the 
technique and gained complete control of the reagents would, of course, 
be dangerous. But the complement fixation reaction furnishes the 
most perfect, biological, diagnostic test yet devised, one in which all 
adverse or disturbing factors can be eliminated and in which a clear 
knowledge of the properties and mode of action of the reagents has 
