PREPARATION OF BACTERIAL ANTIGENS 13 



complementary action of its own. The sediment, on the con- 

 trary, possessed almost the full anticomplementary power of 

 the original suspension, but showed only a slight antigenic 

 value. 



The method is constant in providing a satisfactory antigen 

 preparation without anticomplementary action when applied 

 to the group of organisms in question. The only point in the 

 method at which special care must need be exercised is at the 

 time of centrifugalization. The antigen solution must be centrif- 

 ugalized until it is perfectly clear, otherwise it may still pos- 

 sess a degree of anticomplementary action. 



How far the method is applicable to other types of organ- 

 isms than those here considered has not been extensively de- 

 termined. But that it has a general application seems prob- 

 able from the fact that in a slightly modified form I have by 

 its use succeeded in preparing an antigen from tubercle bacilli 

 with so low an anticomplementary action as to allow its use in 

 a reliable serum diagnosis of tuberculosis in man. 



III. The conservation of antigens without the addition of 

 chemical preservatives. In the preceding section I have 

 given methods by which bacteria may be cultivated for use as 

 antigens, without protein admixture and by which the essential 

 antigenic substances may be released from the bacterial cell 

 without modification by chemical reagents. 



A third necessity in the comprehensive use of antigens for 

 quantitative test-tube determinations is the preservation of a 

 given antigen over a relatively long period without great loss 

 in antigenic value or marked increase in its anticomplementary 

 action. 



The usual method of adding to antigen solutions such chem- 

 ical preservatives as phenol and trikresol has the distinct disad- 

 vantage of inviting progressive chemical changes by these 

 reagents often resulting in precipitates with considerable anti- 

 complementary power. 



A far more dependable method I have found to be the preser- 

 vation of stock antigens in a frozen state. In this method, the 

 perfectly clear antigen solution obtained by centrifugalization 



