December IC, 1904.] 



SCIENCE. 



823 



own special protective device depending 

 upon original capacities of the species 

 which would be gradually developed in 

 power and efficiency with the perfection of 

 parasitic relations. 



The formation of protective or defensive 

 coverings, the strengthening or modification 

 of the cell wall or the secretion of defensive 

 fluids, would account for certain phenom- 

 ena which are familiar to bacteriologists 

 much better than the current theory which 

 bases parasitism exclusively upon toxin 

 production, active or passive. 



In cultures we should expect a loss of 

 power to form protective substances be- 

 cause the antibodies are absent. Hence 

 the universal tendency toward the reduc- 

 tion and final loss of virulence, with ap- 

 parently the metabolic and vegetative ac- 

 tivities unchanged, and the frequently ob- 

 served regaining of virulence by passages 

 through series of animals. 



In the evolution of parasitic bacteria I 

 assume then that though the function of 

 toxin production may have been the enter- 

 ing wedge toAvard a parasitic existence, 

 there is a progressive loss of this function 

 as of little use to the parasite after it has 

 once acquired a foothold, for the action of 

 toxins at a distance from the focus of mul- 

 tiplication does not aid the parasite, while 

 it may destroy the host. In other words, 

 with the invasion of the tissues of the lat- 

 ter it became necessary for the invader to 

 concentrate its powers in its immediate 

 vicinity, and for this purpose those poisons 

 set free by the disintegration of the para- 

 site may be of use in protecting the focus 

 where the younger forms are, by necrosis 

 of tissue, plugging of vessels, etc., and 

 thereby keeping away the bactericidal 

 forces until the bacteria have accumulated 

 sufficient protective power to subsist in a 

 latent condition and are ready to be dis- 

 charged outward. With the loss of active 

 toxin production according to this hypoth- 



esis and the loss of other, now useless, meta- 

 bolic activities, there goes hand in hand a 

 strengthening of the defensive functions. 

 This strengthening I interpret as the grad- 

 ual development of certain siibstances 

 which the non-immune host is unable to act 

 upon or at most only in a slight degree. 

 This substance which, as it were, shoves 

 itself between the parasite and the common 

 bactericidal forces of the body, bears the 

 specific pathogenic character of the mi- 

 crobe. It is the substance which, according 

 to the nomenclature of Ehrlich, calls forth 

 the amboceptor from the resources of the 

 host to combine with it, and thus open the 

 way for the usual bactericidal forces or 

 complements according to Ehrlich. The 

 existence of this specific protective body 

 will account for the varied resistance of 

 animals to the same microorganism and the 

 relative difficulty to induce immunity. The 

 more difficulty the body has in producing 

 the amboceptor the greater the difficulty in 

 acquiring immunity. 



In the departments of preventive and 

 therapeutic medicine, the isolation of this 

 protective substance apart from the body 

 toxins would be of prime importance in 

 combating disease by inducing individual 

 resistance. In fact, the theory that the 

 so-called immunizing and disease-produc- 

 ing substances are separate is not new, 

 but has been presented under various 

 forms. The tendency to give up the toxic 

 extracts of bacteria and use the latter in 

 their entirety in immunization pays tribute 

 to these unknown bodies. The most 

 prominent example of this change was the 

 abandonment by Koch of the old tuber- 

 culin, a boiled extract, and the utilization- 

 of the entire tubercle bacilli ground and 

 uninjured by heat, in the production of 

 immunity in tuberculosis. 



The foregoing hypothesis, that the tend- 

 ency of microbes in perfecting the parasitic 

 habit is to act solely on the defensive, is to 



