144 APPLIED IMMUNOLOGY 



gonococci are grown on salt-free veal-agar, neutral in 

 reaction to phenolphthalein : 24-hour-old cultures are 

 washed oiF the agar-slants with distilled water and the 

 resulting suspension is heated for two hours in a 

 water-bath at 56° C. It is then centrifuged and 

 passed through a Berkefeld filter. No salt is added to 

 this antigen until it is desired to use it, when it is made 

 up to 0.9 per cent, strength by adding one part of 9 per 

 cent, saline solution to nine parts of antigen. Follow- 

 ing Schwartz and McNeil's instructions to the letter, 

 we have prepared monovalent, trivalent and hexa- 

 valent antigens and have employed them compara- 

 tively in a large series of cases with the result that the 

 hexavalent preparation gave the highest percentage of 

 positive results and in every way appeared to be the 

 most reliable of the three antigens. Even with the 

 hexavalent antigen, prepared as described above, we 

 have been forced, in comparative studies, to the con- 

 clusion that it has not been so useful or reliable as 

 when prepared in the following manner : Forty-eight- 

 hour-old cultures of the same six strains of gonococci, 

 grown on blood-agar, were washed off in sterile dis- 

 tilled water ; shaken for one hour ; and autolyzed for 

 twenty-four hours in a thermostat at the temperature 

 of 37° C. and heated in a water-bath at 60° C. for 

 one-half hour. Before use, this antigen is diluted one 

 to ten by the addition of 0.85 per cent, salt solution. 



