THE RELATION OF LIPOIDS TO IMMUNITY 529 



the preparation of antigen other than those previously described are 

 the following: 



1. After securing the alcoholic extract described elsewhere evaporate 

 it to dryness. Again extract in methyl alcohol and evaporate. Extract 

 with warm ether, renewed several times during the course of twenty- 

 four hours. Dry, and repeat the extraction several times until the 

 alcohol remains colorless. Evaporate the alcoholic and ethereal ex- 

 tracts at 50 and 37 C. respectively. A yellowish-red, sticky mass 

 results. Dissolve this in a large amount of water-free ether. Filter, 

 and evaporate at room temperature until a slight powdery precipitate 

 is deposited. This solution constitutes the stock antigen, which, how- 

 ever, may require still further concentration. 



2. A synthetic cancer antigen may be prepared by grinding up 0.5 

 gram of lecithin (ovolecithin Merck, or lecithin Richter), and extract it 

 with 50 c.c. of acetone for twenty-four hours at 50 C. Filter through 

 Scheicher and Schull's filter-paper No. 590, until clear. Just before 

 it is to be used it should be diluted with water in such amount that 1 c.c. 

 will contain the largest amount that does not cause a marked reduction 

 of surface tension in normal serum. As a rule, this dilution is between 

 1 : 50 and 1 : 100 (Kohler and Luger) 1 . 



3. A syphilis antigen may be prepared by extracting 0.5 gram of 

 dried and powdered syphilitic liver with 50 c.c. of absolute alcohol for 

 two hours at 37 C. with frequent shaking. Filter, and concentrate to 

 10 c.c. 



4. A bacterial antigen, as e. g., one of typhoid bacilli, may be prepared 

 as follows : Wash off five forty-eight-hour agar cultures of typhoid bacilli 

 with 5 c.c. of normal salt solution for each tube. Cover the emulsion 

 with toluol, and shake vigorously for several, hours. Place in an in- 

 cubator at 37 C. for forty-eight hours, and filter through a sterile 

 Berkefeld filter. This filtrate may be used as antigen, or it may be 

 used in preparing an alcoholic extract in the following manner: To the 

 original aqueous filtrate add 50 c.c. of absolute alcohol. Allow the 

 mixture to stand for one-half hour, shake, centrifugate, and then mix 

 the sediment with 20 c.c. of absolute alcohol. Shake thoroughly once 

 more, and again centrifugate. Combine the two extracts, and con- 

 centrate on the water-bath to about 20 c.c. 



Practical Value. This test is quite delicate, and errors due to faulty 

 technic are quite likely to creep in. Unless all precautions are rigidly 

 observed, the results are worthless. Although an extensive literature 



1 Wien. klin. Wochenschr., 1912, 25, 1114. 

 34 



