AGGRESSINS 185 
in the form of the hemolytic system is employed to render the end-result 
visible. Indeed, it is possible to add the hemolytic system to completed 
Kahn tests and obtain complement-fixation results, similar to the 
original Kahn results, indicating that the two methods detect the 
same reagin in syphilitic serum. 
With regard to the clinical interpretation of the Kahn procedures: 
The routine diagnostic test is of conservative sensitiveness similar to 
that of a reliable Wassermann test. Some workers claim that the 
Kahn is more sensitive than the Wassermann in early primary and in 
treated cases. The quantitative procedure is of especial value in 
checking the effect of antisyphilitic treatment. The qualitative spinal- 
fluid procedure is also similar in sensitiveness to a reliable Wassermann 
test in neurosyphilis. The quantitati^'e spinal-fluid procedure is of 
especial value as a check on treatment in neurosyphilis. 
AGGRESSINS. 
Progressively pathogenic bacteria appear to differ from parasitic 
bacteria or "opportunists" in that they are able to force an entrance 
to the underlying tissues of the host through natural, non-specific 
barriers which ordinarily suffice to restrain the more parasitic types 
of microbes. Bail^ has advanced an hypothesis, based upon experi- 
mental evidence, which attributes the invasiveness of pathogenic 
bacteria and their ability to develop in the tissues of the host to 
"aggressins." These aggressins, according to Bail, are present and 
may be demonstrated in exudates resulting from bacterial infection, 
but they are not, as a rule, found in artificial cultures of the same 
organism. To demonstrate the action of aggressins, Bail removed 
bacteria from exudates by centrifugalization and injected the clear 
supernatant fluids, together with a sublethal dose of the homologous 
bacterium, into experimental animals. Rapidly fatal infections devel- 
oped. The aggressin-containing exudates were not inactivated by 
prolonged exposure to 50° C, and it was shown, furthermore, that 
their injection into susceptil)le animals stimulated the formation of 
"antiaggressin," which greatly increased the resistance of the animal 
to subsequent infection. The sera of animals immunized with aggres- 
sin-containing fluids conferred a limited degree of immunity to specific 
infections in non-immune animals (passive immunity). It has been 
claimed by Doerr^ and others that the aggressins are of the nature of 
bacterial endotoxins and that the immunizing properties of aggressin 
fluids are due to their content of specific substances derived from the 
autolysis of bacterial cells. 
The aggressin theory must, for the present, be regarded as not 
definitely proved. 
1 See Bail (Das Problem der bakteriellen Infektion, Bibliothek medizinischer Mono- 
graphien, 1911, vol. 11); see also Miiller in Oppenheimer's Handbuch der Biochemie, 
1909, 2, 1, 681. 
2 Wien. klin. Wchnschr., 1906, 19, 759; Centralbl. f. Bakt., orig., 1906, 41, 497. 
