454 MICROBIOLOGY 



Aggressin. Bail 23 in studying the problems of virulence 

 and immunity for the purpose of explaining the so-called 

 ' ' phenomenon of Koch ' ' * found that if tubercle bacteria were 

 injected, together with sterilized tuberculous exudate, into 

 healthy guinea pigs they died within 1 to 2 days. When the 

 exudate was injected alone it produced no appreciable effect 

 and when the tubercle bacteria were injected alone they pro- 

 duced death from tuberculosis in the usual time. His conclu- 

 sion was that there is something in the exudate that allows 

 the bacteria to become more aggressive and to this substance he 

 assigned the name aggressin. He believed this substance to be 

 an endotoxin liberated by the bacteria and that its effect is to 

 paralyze the polynuclear leucocytes thereby inhibiting phago- 

 cytosis. Heating the exudate to 60 C. increased rather than 

 diminished its aggressive properties. According to Bail, sev- 

 eral of the pathogenic bacteria such as Micrococcus pyogenes, 

 the bacterium of chicken cholera, and the typhoid bacillus, pro- 

 duce aggressins which can be found in the exudates occurring 



upon a s'ide. The mixture is then drawn into the pipette; the end is 

 sealed; and incubation at 37.5 degrees is carried on for an arbitrary 

 time, usually fifteen to thirty minutes. The control with normal 

 serum is treated in exactly the same way. After incubation the end 

 of the pipette is broken off, the contents are again mixed, and 

 smears are made upon glass slides in the ordinary manner of blood 

 smearing. Staining may be done by Wright's modification of Leish- 

 man's stain, by Jenner's, or by any other of the usual blood stains. 

 In these smears, then, the number of bacteria contained in each 

 leucocyte is counted. The contents of about eighty to one hundred 

 ceiis are usually counted and an average is taken. This average 

 r umber of bacteria in such leucocytes is spoken of as the 'phago- 

 cytic index.' The phagocytic index of the tested serum, divided by 

 that of the 'normal pool' (control) serum, gives the 'opsonic 

 index'." 



23 Bail. Arch. f. Hyg., Bd. LII, p. 272, 411. 

 Zeit. f. Hyg., (1905 i.) No. 3. 



* Koch observed in his early investigations on tuberculosis that 

 tuberculous animals when inoculated intraperitoneally with fresh 

 cultures of tubercle bacteria died quickly from an acute attack of 

 the disease and the resulting intraperitoneal exudate was composed 

 almost exclusively of lymphocytes. 



