10 MELICK 



Wassermann and Bruck, 5 Citron, 6 Wassermann, 7 and by 

 Leucles. 8 



Thus it early became recognized that the products of bac- 

 terial disintegration were to be preferred to intact bacterial 

 cells in the preparation of antigens for test tube determinations 

 by the complement fixation method. Of the many means used 

 in the attempt to obtain a suitable disintegration, autolysis is 

 perhaps the oldest. Mechanical procedures such as grinding 

 the dried organisms, either alone or admixed with a cutting 

 material such as sand have also been extensively employed. 

 In general, these processes are of slight efficiency. Direct 

 treatment by chemical reagents has also been resorted to, the 

 organism often being subjected to the action of alcohol, ether, 

 chloroform, antiformin or the proteolytic ferments. In the 

 more recent attempts to obtain thorough disintegration, the 

 several procedures have been combined as in Besredka's 

 method by Gay, where alcoholic precipitation, desiccation and 

 grinding with sodium chloride crystals are resorted to, in 

 order. 



None of these methods is more than partially satisfactory in 

 obtaining favorable antigen products from bacterial cells. In 

 the case of the mechanical procedures, the yield of cell-free 

 antigen is slight. In the case of the chemical methods a modi- 

 fication of the antigenic bacterial proteins by the reagents em- 

 ployed is sure to occur and may in any given instance be suffi- 

 cient to change the antigenic properties of the native proteins. 

 This latter point, I cannot emphasize too strongly; for it has 

 been disregarded with great regularity. If there is one general- 

 ization which can be made concerning antigenic substances, 

 it is that they are protein in structure; and equally valid is the 

 observation that as such, they are highly susceptible to modi- 

 fication by chemical reagents. The marked specificity of the 

 antibody-antigen reaction demonstrates in itself the delicacy of 

 the chemical differences which determine characteristic anti- 

 genic properties. That these differences are readily modified 

 by chemical reagents is shown by the work of Pick, 9 Kahn 

 and McNeil, 10 Perry and Kolmer n and others. There is no 

 guarantee that any cell protein subjected to reagents such as 



