ch we are testing, but
rather a physical-chemical change in the serum of patients with
syphilis, which can be produced by other things besides this one
disease. But this fact has not impaired the practical value of the test,
since the other conditions which give it are not likely to be confused
with syphilis in this part of the world. The fact that no true antibody
is formed simply makes it unlikely that we shall ever have a vaccine for
syphilis.

+Difficulties of the Test.+--The Wassermann blood test for syphilis is
one of the most complex tests in medicine. The theory of it is beyond
the average man's comprehension. A large number of factors enter into
the production of a correct result, and the attaining of that result
involves a high degree of technical skill and a large experience. It is
no affair for the amateur. The test should be made by a specialist of
recognized standing, and this term does not include many of the
commercial laboratories which spring up like mushrooms in these days of
laboratory methods.

+The Recognition of Syphilis by the Blood Test.+--When the Wassermann
test shows the presence of syphilis, we speak of it as "positive."
Granted that the test is properly done, a strong positive reaction means
syphilis, unless it is covered by the limited list of exceptions. After
the first few weeks of the disease, and through the early secondary
period, the blood test is positive in practically all cases. Its
reliability is, therefore, greatest at this time. Before the infection
has spread beyond the first sore, however, the Wassermann test is
negative, and this fact makes it of little value in recognizing early
primary lesions. In about 20 to 30 per cent of syphilitic individuals
the test returns to negative after the active secondary stage is passed.
This does not necessarily mean that the person is recovering. It is even
possible to have the roof fall out of the mouth from gummatous changes
and the Wassermann test yet be negative. It is equally possible, though
unusual, for a negative Wassermann test to be coincident with contagious
sores in the mouth or on the genitals. So it is apparent that as an
infallible test for syphilis it is not an unqualified success. But
infallibility is a rare thing in medicine, and must be replaced in most
cases by skilful interpretation of a test based on a knowledge of the
sources of error. We understand pretty clearly now that the Wassermann
test is only one of the sign