I. S. FALK 573 



sistant animals on the growth of pneumococci in serum-leukocyte mixtures is an- 

 nulled by the addition of specific soluble substance. Felton and Bailey' have reported 

 that injections of only partially purified soluble substance into mice renders them 

 more susceptible to partly attenuated pneumococci (or enhances the virulence of the 

 organisms), and that the protective substance of antiserum or antibody solution is 

 neutralized by specific soluble substance. Inasmuch as it is tentatively considered by 

 most investigators that the soluble substances are associated with the capsular 

 structure of bacteria, these observations would harmonize with those on P.D., be- 

 cause of the parallelisms of virulence, P.D., and encapsulation, and because the gen- 

 erally accepted theory of electrophoresis locates the basis of the electrokinetic be- 

 havior on the surface layers of the particle. 



In apparent contradiction to these views, however, there are observations which 

 we have made repeatedly that: 



1. Filtrates from virulent pneumococcus cultures which had been incubated long 

 enough to contain high concentrations of specific, soluble substance do not significant- 

 ly enhance the virulence of less virulent cultures for mice; and they do not reduce 

 the resistance of mice to such cultures. 



2. Preparations of purified soluble substance are not toxic for mice, and are not 

 more active than culture filtrates. 



3. Preliminary experiments indicate no significant effects of soluble substances on 

 P.D. 



4. The significant differences in suspension stability, motility, etc., between "S" 

 and "R" cultures appear not to be determined by the menstruum, although when this 

 comes from "S" type bacteria it contains specific substance, and lacks this reagent 

 when it comes from the "R" type.^ 



It must be considered at this time that the role of specific, soluble substances in 

 determining virulence is still uncertain; but the indications are that the secreted sub- 

 stances are probably unimportant, although the specific substances contained in or on 

 the cell may be determining factors. It is also probable that a common mechanism 

 (of a genetic order) determines the production of soluble substances, encapsulation, 

 cell and colony morphology, motility, and P.D. 



TOXIGENICITY AND ELECTROPHORETIC POTENTIAL 



The general parallelisms between P.D. and virulence characteristics of non- 

 toxigenic organisms suggest the question whether similar parallelisms obtain for toxi- 

 genic organisms. Corynebacteria were chosen for an investigation of this problem in 

 my laboratory. 



If it be assumed that the P.D. has its origin in phenomena of semi-permeability of 

 the kind encountered in Donnan membrane equilibria, the a priori argument takes 

 the following form: 



I. Assuming that for different strains high toxigenicity grades by imperceptible 

 degrees through low to no demonstrable toxigenicity;^ 



' Felton, L. D., and Bailey, G. H.: /. Infect. Dis., 38, 131. 1926. 



^ These experiments are being extended now. 



3 This is entirely in accord with the experimental findings. 



