122 IMMUNE SERA 



product is obtained which is not quite as good as 

 that obtained at ice-box temperature. It is pos- 

 sible to prepare the antigen in many ways, using 

 beef heart, human heart, etc., or by using solvents 

 other than alcoho 1 Two types of antigen which 

 are used to a certain extent in some laboratories 

 are the acetone insoluble and the cholesterin for- 

 tified antigens. The first is prepared by adding 

 acetone to the alcoholic extract and using the pre- 

 cipitate which finally settles out. The cholesterin 

 antigen is prepared by adding -$ per cent of choles- 

 terin to the simple alcoholic extract. The acetone 

 insoluble antigen will be found to give fewer posi- 

 tive reactions than the alcoholic extract. The 

 cholesterinized antigen has been found to give a 

 small percentage of positive reactions in cases 

 which are undoubtedly not syphilitic. For use 

 the antigen is diluted as follows: i cc. of the alco- 

 holic extract is placed in a perfectly dry bottle and 

 25 cc. of normal saline added. It is important to 

 add the first 5 cc. of saline, drop by drop, mixing 

 the two by gentle shaking between each addition; 

 the result will be an opalescent, cloudy mixture. 

 The efficacy of this reagent depends to a consider- 

 able extent upon the care with which this dilution 

 is carried out. The amount to be used in the test 

 is determined as follows: The quantities given are 

 such as will make the final bulk of the test .7 cc. 

 Six tubes are placed in a rack and to the first is added 



