536 INFECTION AND RESISTANCE 



working out of serum experiments in which the reasoning from the 

 beginning and the technique finally developed were physical rather 

 than chemical. Perhaps the earliest phases of such work were those 

 in which complement fixation was shown to occur when complement 

 was brought together with non-specific inorganic and organic 

 colloids. It is due chiefly to the work of Landsteiner and his 

 associates that attention was called to such phenomena. Landsteiner 

 with Stankovic showed that complement may be fixed by silicic acid, 

 and Seligmann soon afterwards found that in the precipitation of 

 mastic suspensions complement may be fixed. Much work has been 

 done by others, as well as by ourselves, that shows that a variety of 

 colloidal suspensions of known chemical constitution fix complement, 

 probably by adsorption. Perhaps the most striking instance of such 

 complement adsorption is that occurring in the Wassermann re- 

 action. Here, as we know, complement is fixed by a combination of 

 syphilitic serum and various lipoidal suspensions, which may be en- 

 tirely non-specific in origin. When the reaction occurs, as Jacob- 

 stahl and, later, Bruck have shown, a precipitation occurs which 

 can be seen in the ultramicroscope. Furthermore, this precipitation 

 takes place more rapidly in the ice-chest than in the incubator, a 

 principle upon which is based the so-called refrigerator method of 

 performing the test, and which strikingly suggests that the reaction 

 is an adsorption rather than a true chemical union. It is this pre- 

 cipitate which fixes the complement ; whether or not this is due to 

 quantitatively increased globulin or to purely physical change in the 

 syphilitic serum, is a matter which we cannot discuss at present. 

 Whatever it is, it is unquestionable that the availability of the anti- 

 gen for the Wassermann reaction depends not only upon its lipoidal 

 nature but also on its state of dispersion. Since it is not possible, 

 as we have found, to make available antigens for this reaction with 

 non-lipoidal substances, like mastic, gelatin, gum arabic, salicic acid, 

 albumins, and a number of other substances, even when in dispersion 

 more or less similar to that of the Wassermann antigen, it seems that 

 the secret of the Wassermann antigen must lie in the fact that sub- 

 stances of the chemical and physical constitution of lipoids when 

 brought into a definite state of dispersion offer surface tension con- 

 ditions not easily obtained with colloids of another nature. It is, 

 therefore, at least in our opinion at present, the physical condition 

 of the AVassermann antigen which makes it available for the test, a 

 physical condition which is secondarily dependent upon the chemical 

 nature of the dispersed substance. The importance of the state of 

 dispersion and therefore the surface tension properties is quite ap- 

 parent from the fact noted by many Wassermann workers that a con- 

 siderable difference in the fixing power of the antigen may be ob- 

 tained by in one case adding the salt solution to the alcoholic ex- 

 tract quickly, and in another case adding it very slowly, the two 



