A REVIEW OF OUR PRESENT KNOWLEDGE CONCERNING THE SERO-DIAGNOSIS OF GENERAL PARALYSIS.

BY ERNEST JONES, M. D., M. R. C. P. (Lond.),

Demonstrator of Psychiatry, University of Toronto; Pathologist to the Toronto Hospital for the Insane.

As the subject of sero-diagnosis is one which in general is alien to the field studied by the psychiatrist, in presenting a critical review of its application to the diagnosis of mental disease it will be desirable briefly to consider some of the more elementary of the principles on which it is based. Of the various new methods that may be grouped under the designation of sero-diagnostic tests the one known as Wassermann's reaction is by far the most important, so that it will have to be considered at greatest length. The essence of Wassermann's discovery can be shortly stated: The blood serum of a syphilitic, when mixed with an infusion made from syphilitic material, has the power of binding the complement " of normal blood serum. To appreciate the significance of this observation it is necessary to recall the following facts concerning the nature of "complement."

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If living material, e. g., red blood cells, bacteria, serum albumin, etc., is injected into an animal, the blood plasma of this animal acquires the property of reacting in vitro to corresponding material (which is called "antigen") in certain definite ways. For instance, if red blood cells constitute the antigen then the blood serum of the animal into which they have been injected will acquire the capacity of dissolving such cells when added to them in a test tube, in other words, of bringing about hæmolysis. If the antigen is one which, like red blood cells, is obtained from an animal, then the injection must be into an animal of a different species from the first. The serum becomes "inactivated," that is to say it loses this newly-acquired capacity, on being heated for half an hour at 56° C. This inactive serum, however, essentially differs from that of a normal animal, for if a small portion of