IMMUNITY REACTIONS 



203 



dilute alkali salts, these salts cause a precipitation of agglutinated 

 bacteria as they would a suspension of kaolin or mastic. This was 

 demonstrated by H. BECHHOLD* 1 as well as M. NEISSER and U. 

 FRIEDEMANN*, and practically confirmed by B. H. BUXTON, P. 

 SHAFFER and O. TEAGUE*, as well as by B. H. BUXTON and A. H. 

 RAHE*. 



Capsulated bacteria possess, in their mucous capsules, a natural 

 protective colloid and accordingly, they are not agglutinated by 

 immune serum even in suspensions containing salt. O. FORGES 

 showed that if the mucous capsules were removed by gently heating 

 them with dilute hydrochloric acid, even capsulated bacteria were 

 agglutinated by immune sera. 



As in the case of the precipitins, a certain quantitative rela- 

 tionship between bacteria and agglutinating serum is required for 

 precipitation. But in this instance, there are certain irregularities 

 as regards native and heated sera. 



This phenomenon also has its analogue in the precipitation of 

 unorganized suspensions in the presence of protective colloid. Table I 

 (see below) illustrates the agglutination of bacteria by diluted immune 

 serum. Table II illustrates the precipitation of a mastic suspension 

 by A1 2 (804)3 in the presence of leech extract as a protective colloid. 



These " irregular series" (see p. 84) frequently occur in the pre- 

 cipitation of suspensions by ferric chlorid, aluminium chlorid and 

 certain dyes. They are explained by the fact that the hydrolytically 

 split iron oxid hydrosol, etc., functions as a " protective colloid/' and 

 in certain proportions interferes with the precipitation. If still an- 

 other protective colloid (gelatin, leech extract, etc.) is added, the 

 circumstances are still further complicated as shown by Table II. 



TABLE I. 



TABLE II. 



Agglutination of typhoid bacilli with 

 very dilute immune serum. (After 

 EISENBERQ and VOLK.) 



Precipitation of mastic suspension 

 by 0.0002 c.c. j A1 2 (SO 4 )3 in the 



presence of leech extract as pro- 

 tective colloid. (After M. NEIS- 

 SER and U. FRIEDEMANN, and H. 

 BECHHOLD.) 



