INFECTIONS OF THE DIGESTIVE TRACT 161 



were obtained from the peritoneal exudate and carefully 

 separated from cellular elements by the centrifuge. 

 It was found that numbers of typhoid or cholera bacilli 

 below the fatal dose become fatal when injected simul- 

 taneously with "aggressins," that it is possible by means 

 of "aggressins" to inhibit the protective action of a 

 bacterial immune serum in the peritoneal cavity of the 

 guinea-pig, and, finally, that one may by suitable treat- 

 ment with "aggressins" induce immunity to fatal 

 doses of typhoid or cholera bacilli. Bail regards this 

 "aggressin" immunity as something distinct from a 

 bactericidal immunity because a bacterial immune serum 

 does not protect against "aggressins," but very recent 

 studies by Wassermann and Citron 1 indicate that 

 "aggressins" are really bacterial extracts, and that their 

 influence in promoting infection depends on their ability 

 to bind defensive substances largely derived from leu- 

 cocytes and designated complements in Ehrlich's ter- 

 minology. It is not yet clear whether the "aggressins" 

 really act through binding complements in vivo or not, 

 and this is a crucial point. 2 Hence we cannot feel certain 

 how to interpret Sir A. E. Wright's observations on the 

 immunization of English soldiers against typhoid fever, 

 in which he met with at least a measure of success by 



1 Wassermann and Citron, " Ueber die Bildungsstatten der 

 Typhusimmunkorper," Zeitschr. f. Hyg., 1, p. 331, 1905; Citron, 

 "Ueber nattirliche und kiinstliche Aggressine," Centralbl. f. 

 Bakt., I Abt., Orig., xli, p. 230, 1906; "Die Immunisierung gegen 

 die Bakterien der Hogcholera (Schweinpest) mit Hilfe von Bak- 

 terienextrakten," Zeitschr. f. Hyg., liii, p. 515, 1906. 



2 Wolff-Eisner, "Die Aggressinlehre," Centralbl. f. Bakt., I Abt., 

 Ref ., xxxviii, p. 641, 1906. 



K 



