AGGRESSINS 165 



of antigen (1 to 20 dilution in salt solution). 1 The total volume of 

 complement and antigen is brought to 3 c.c. by the addition of salt 

 solution. After one hour's incubation in the water bath at 37 C., 1 

 c.c. of sheep erythrocyte suspension and 1.5 units sheep erythrocyte 

 hemolysin are added and reincubated. That dilution of antigen which 

 shows the slightest inhibition of hemolysis is taken as the anti- 

 complementary titer of the antigen. Not more than one-half this 

 amount, and preferably one-fourth of the anticomplementary titer, 

 is used in the test. 



The actual determination is made in the same manner as for the 

 Wassermann test. 2 It is well to include a known positive and known 

 negative glanders serum of the same animal species as the unknown, 

 together with suitable controls of the hemolytic system. The length 

 of incubation is determined by the time it takes to effect complete 

 hemolysis in the known negative and the hemolytic controls. Fre- 

 quently ten or more hours will elapse before this occurs. 



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 3 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 

 developed. The aggressin-containing exudates were not inactivated 

 by prolonged exposure to 50 C., and it was shown, furthermore, that 



1 Usually a range of antigens from 2 c.c. to 0.05 c.c. will be found sufficient. 



2 For full discussion of results, see Mohler and Eichhorn, Bureau of Animal Industry 

 Bulletin 136, April 7, 1911. 



3 See Der Problem der bakteriellen Infektion, Bail, in Bibliothek medizinischer Mono- 

 graphien, xi; see also Miiller in Oppenheimer's Handbuch der Biochemie, 1909, ii, 1, 

 681. 



