It seems desirable at this point, while we are trying to fix in mind the great value of recognizing syphilis in a person in order to treat it and thus prevent dangerous complications, to say something about the blood test for syphilis, the second great advance in our means of recognizing doubtful or hidden forms of the disease. The first, it will be recalled, is the identification of the germ in the secretions from the early sores.

Antibodies in the Blood in Disease.—It is part of the new understanding we have of many diseases that we are able to recognize them by finding in the blood of the sick person substances which the body makes to neutralize or destroy the poisons made by the invading germs, even when we cannot find the germs themselves. These substances are called antibodies, and the search for antibodies in different diseases has been an enthusiastic one. If we can by any scheme teach the body to make antibodies for a germ, we can teach it to cure for itself the disease caused by that germ. So, for example, by injecting dead germs as a vaccine in typhoid fever and certain other diseases, we are able to teach the body to form protective substances which will kill any of the living germs of that particular kind which gain entrance to the body. Conversely, if the body is invaded by a particular kind of germ, and we are in doubt as to just which one it is, we can identify it by finding in the blood of the sick person the antibody which we know by certain tests will kill or injure a certain germ. This sort of medical detective work was first applied to syphilis successfully by Wassermann, Neisser, and Bruck in 1904, and for that reason the test for these antibodies in the blood in syphilis is called the Wassermann reaction. To be sure, it is now known that in syphilis it is not a true antibody for the poisons of the SpirochÆta pallida for which 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 signs of syphilis and that it has quite well-understood limitations. It has revealed an immense amount of hidden syphilis, and in its proper field has had a value past all counting. Experience has shown, however, that it should be checked up by a medical examination to give it its greatest value. Just as all syphilis does not show a positive blood test, so a single negative test is not sufficient to establish the absence of syphilis without a medical examination. In a syphilitic, least of all, is a single negative Wassermann test proof that his syphilis has left him. In spite of these rather important exceptions, the Wassermann test, skilfully done and well interpreted, is one of the most valuable of modern medical discoveries.

The Blood Test in the Treatment and Cure of Syphilis.—In addition to its value in recognizing the disease, the Wassermann test has a second field of usefulness in determining when a person is cured of syphilis, and is an excellent guide to the effect of treatment. Good treatment early in a case of syphilis usually makes the Wassermann test negative in a comparatively short time, and even a little treatment will do it in some cases. But will it stay negative if treatment is then stopped? In the high percentage of cases it will not. It will become positive again after a variable interval, showing that the disease has been suppressed but not destroyed. For that reason, if we wish to be sure of cure, we must continue treatment until the blood test has become negative and stays negative. This usually means repeated tests, over a period of several years, in connection with such a course of treatment as will be described later. During a large part of this time the blood test will be the only means of finding out how the disease is being affected by the treatment. To all outward appearance the patient will be well. He may even have been negative in repeated tests, and yet we know by experience that if treatment is stopped too soon, he will become positive again. There is no set rule for the number of negative tests necessary to indicate a cure. The whole thing is a matter of judgment on the part of an experienced physician, and to that judgment the patient should commit himself unhesitatingly. If a patient could once have displayed before him in visible form the immense amount of knowledge, experience, and labor which has gone into the devising and goes into the performing of this test, he would be more content to leave the decision of such questions to his physician than he sometimes is, and would be more alive to its reality and importance. The average man thinks it a rather shadowy and indefinite affair on which to insist that he shall keep on doctoring, especially after the test has been negative once or twice.

Just as a negative test may occur while syphilis is still actively present and doing damage in the body, so a positive Wassermann test may persist long after all outward and even inward signs of the disease have disappeared. These fixed positives are still a puzzle to physicians. But many patients with fixed positives, if well treated regardless of their blood test, do not seem to develop the late accidents of the disease. If their nervous systems, on careful examination, are found not to be affected, they are reasonably safe as far as our present knowledge goes. People with fixed positives should accept the judgment of their physicians and follow their recommendations for treatment without worrying themselves gray over complications which may never develop.

Practical Points About the Test.—Certain practical details about this test are of interest to every one. Blood for it is usually drawn from a small vein in the arm. The discomfort is insignificant—no more than that of a sharp pin-prick. Blood is drawn in the same way for other kinds of blood tests, so that a needle-prick in the arm is not necessarily for a Wassermann test. There is no cutting and no scar remains. The amount of blood drawn is small and does not weaken one in the least. The test is done on the serum or fluid part of the blood, after the corpuscles are removed. It can also be done on the clear fluid taken from around the spinal cord, and this is necessary in certain syphilitic nervous diseases. There is nothing about the test that need make anybody hesitate in taking it, and it is safe to say that, when properly done, the information that it gives is more than worth the trouble, especially to those who have at any time been exposed, even remotely, to the risk of infection. But the test must be well done, by a large hospital or through a competent physician or specialist, and the results interpreted to the patient by the physician and not by the laboratory that does the test, or in the light of the patient's own half-knowledge of the matter.