The virulent cholera spirillum possesses a greater number of bacteriolytic and agglutinable haptophore groups, or these groups are endowed with a greater avidity for uni- and amboceptors than the avirulent.
The number or the avidity of the bacteriolytic receptors possessed by a bacterium is directly proportional to its virulence.
However, the agglutinable receptors do not follow this law, i.e., the agglutinable haptophore groups are not necessarily present in the same proportion as the bactericidal ones.
While the energy of growth is a very important factor in relation to virulence, other phenomena must also be considered.
The virulent organism possesses a greater number of toxic haptophore groups than the avirulent.
The binding power of the free receptors of the organisms for bacteriolytic amboceptors in vitro is proportional to the bactericidal immunity produced in animals by each, which latter is in turn proportional to the virulence of the organisms from which the receptors were extracted. The binding power in vitro of the dead micro-organisms of different virulence for bacteriolytic amboceptors is not in proportion to their toxicity. The bactericidal immunity obtained by means of the inoculation with the dead organisms of different virulence, or their extracts obtained by autolytic digestion, is proportional to the virulence of the living strains of the bacteria employed.
With the living organisms, while the bactericidal immunity obtained from the inoculation of animals with the virulent organism is greater than that produced with the avirulent, such immunity is not in direct proportion to the virulence of the bacteria introduced.
These conclusions apply to the two strains of cholera spirilk employed in the foregoing experiments. Whether they will also hold good with other strains of this spirillum or for micro organisms in general, must be decided by further experimenta work.