306 IMMUNOLOGICAL METHODS OF DIAGNOSIS 



have been well satisfied with the results. Of late several investiga- 

 tors have drawn attention to the fact, however, that by the addition 

 of cholesterin to alcoholic extract of non-syphilitic organs antigens 

 are obtained which are more sensitive than the ordinary alcoholic 

 extract and practically as good as those derived from syphilitic fetal 

 liver the acknowledged standard of the past. Kolmer, Laubaugh, 

 Casselman, and Williams, who have recently investigated the rela- 

 tive merits of the different antigens, both cholesterinized and non- 

 cholesterinized, classify them as follows in the order of their reactive 

 value : 



1. Cholesterinized alcoholic extract of human, pig, and beef 

 heart, named in the order of efficiency and safety. 



2. Plain alcoholic extract of syphilitic fetal liver. 



3. Acetone-insoluble lipoids (Noguchi). 



4. Plain alcoholic extract of human, pig, and beef heart. 



5. Acetone extract of syphilitic liver. 



6. Plain alcoholic extract of normal liver. 



During the past six months I have been working with alcoholic 

 cholesterinized extracts of beef heart side by side with antigens 

 prepared from the same source according to Noguchi 's method, 

 and find that the former is more sensitive than the latter, but that 

 its own anticomplementary properties are sufficient to give rise 

 to more frequent slight reactions with non-syphilitic sera than are 

 seen with the Noguchi antigen. For the present I have accordingly 

 decided to continue the use of the two kinds side by side, and to 

 disregard the slight reactions with which every laboratory worker 

 no doubt is familiar from his experience with antigens from whatever 

 source. 



Preparation of the Different Types of Antigen. (a) The Noguchi 

 Antigen. Fifty or a hundred grams of beef heart, liver, or kidney 

 are passed through a meat-hashing machine and extracted with 

 ten times the amount of absolute alcohol by standing for several 

 days at incubator temperature. The resultant mixture is filtered 

 through ordinary filter paper, the filtrate evaporated to dryness 

 with the aid of an electric fan, the residue taken up with as little 

 ether as possible, and the ethereal solution treated with five times 

 its volume of acetone. A precipitate forms, which is allowed to 

 settle to the bottom, when the supernatant fluid is poured off. From 

 the remaining brown, sticky material a saturated solution is pre- 



