104 INFECTION 



typhoid fever, the typhoid bacillus resists agglutination, whereas it 

 becomes easily agglutinable after a period of artificial cultivation. It 

 may be assumed that, when active, the bacillus as an infecting agent 

 gradually became more resistant against the agglutinating properties 

 of the patient's serum, and that, when grown on artificial media, it loses 

 this resistance by being removed from the stimulating influence of the 

 infected body. 



This hypothesis, however, would go a step further in assuming the 

 possibility of the receptors of the invading bacteria anchoring certain 

 constituents of our body-fluids, and being stimulated to the production 

 of various cytotoxins, which attack the leukocytes, erythrocytes, nerve- 

 cells, liver, kidney, etc. In other words, each bacterium may be con- 

 ceived as being composed of a central atom group with numerous side- 

 chains, just as Ehrlich conceived the hypothetic structure of body-cells, 

 and that these side-chains, primarily present for the purpose of anchor- 

 ing food material, may likewise anchor various pathogenic animal sub- 

 stances, with the production of substances acting as antibodies to the 

 opposing forces of the host. Welch assumed that these bodies were of 

 the nature of amboceptors, which may become complemented by bac- 

 terial complement or by endocomplements of the tissue-cells; this is of 

 secondary importance, and there is no reason why they may not be of 

 different structure, and similar to all three orders of antibodies produced 

 by body-cells according to Ehrlich's side-chain theory of immunity. 



This hypothesis may possibly explain certain instances of so-called 

 species and organ virulence, whereby the virulence of an organism arti- 

 ficially increased by repeated passage through animals of the same spe- 

 cies, does not manifest this increased virulence for animals of different 

 species. If, for example, the virulence of the chicken cholera bacillus 

 is increased by repeated passage through the chicken, the increase of 

 virulence affects this animal, but does not affect the guinea-pig. Certain 

 organs may likewise be subject to a similar selective virulence, if the 

 increase in virulence has been induced by the specific intervention of 

 those organs, and this selective virulence shows itself, irrespective of 

 the manner in which the infection was produced. 



That virulence of this order is playing an important role in the pro- 

 cesses of infection is a theory supported by the discovery that different 

 strains of the same species of bacteria are found to produce characteristic 

 lesions, and while this affinity for a certain organ may be natural and 

 inherent, there can be no doubt that it may also be experimentally 

 induced and acquired. For example, according to Rosenow, a certain 



