APPLICATION OF COMPLEMENT FIXATION 189 



been demonstrated by clinical examination. It is useful, how- 

 ever, as a control of other antigens with which doubtful results have 

 been obtained. 



The source of the lecithin appears to play some role in its value as an 

 antigen; that from heart is most active, while that from liver, brain 

 and egg yolk follow in the order named. An extract such as that 

 recommended by Noguchi contains in all probability a mixture of lipoids 

 and unsaturated fatty acids; Noguchi and Bronfenbrenner found the 

 fixing capacity of such extracts to vary in accordance with the content 

 of unsaturated fatty acids. Browning and Cruikshank found that the 

 addition of cholesterol to the antigen augments the delicacy of the re- 

 action and this method has found widespread use in this country, 

 particularly through the work of Walker and Swift. The latter investi- 

 gators recommend the addition to alcoholic extracts of human or 

 guinea-pig hearts of 0.4 per cent, of cholesterol. In the hands of sev- 

 eral workers this has so increased the fixing power of the antigen as 

 to give positive results in the presence of non-syphilitic serum, the 

 so-called false positive reactions, and with the development of the 

 method of fixation at refrigerator temperature, to be described subse- 

 quently, it has been discarded in several laboratories. Nevertheless, the 

 cholesterolized antigens are found, in the hands of numerous workers, 

 to show much less variation in fixing capacity than the non-cholesterol- 

 ized extracts and for this reason are recommended for routine 

 laboratory work. 



It would appear that the antigenic substance in the Wassermann test 

 is not an antigen in the biological sense, for it can be obtained from 

 tissues not the seat of a syphilitic infection and as has been shown by 

 Fitzgerald and Leathes, upon injection into animals it does not lead to 

 the formation of immune substances. 



The methods of preparing syphilitic antigens have been multiplied 

 in great number and cannot be included in the scope of this book. Sim- 

 plification of preparation has been attempted with variable results. 

 Of interest is the method suggested by Ecker and Sasano. They quote 

 Neymann and Gager to the effect that primary extraction of the tissue 

 with ether removes substances of anti-complementary power but only a 

 small amount of the lecithin. Ecker and Sasano suggest three ten- 

 minute extractions with ether in the proportion of 25. grams ground 

 and dried heart muscle to 50. c.c. ether. The material is then extracted 

 for one hour with 75. c.c. 95 per cent, ethyl alcohol at boiling tempera- 

 ture (78 C.) in a flask connected with a reflux condenser. An antigen 

 of this sort has retained its original fixing power in this laboratory 

 after more than a year. 



Nature of Syphilitic Antigen. Extracts of the treponema pallidum 

 may serve as antigens and are true antigens in the biological sense. 

 Craig and Nichols, however, found that alcoholic extracts of organ- 

 isms closely related to treponema pallidum, as the treponema per- 

 tenue and the treponema microdentium, may fix complement in the 

 presence of syphilitic serum. Extracts of animal and human 



