Acquired immunity against micro-organisms 297 



or the amboceptors of Ehrlich. On a fresh arrival of the same 

 micro-organisms, they meet with, in the fluid of the exudations, 

 numerous amboceptors which combine with the corresponding 

 receptors of the micro-organisms, without, however, destroying them 

 or interfering with their vitality. As these amboceptors possess still 

 a second affinity, that for the molecules of the cytases, or the 

 " complements " of Ehrlich, the micro-organisms can be placed in 

 contact with these soluble ferments. Without the intervention of the 

 fixatives, the combination of the body of micro-organisms with the 

 cytase can never take place, because the receptors of the micro- 

 organisms are not adapted to those of the cytases. When the 

 molecules of these ferments are found in the plasmas in a free 

 state, they can be attacked by the corresponding group of the 

 amboceptors. 



Let us compare the theory we have just sketched with that 

 described further back. The micro-organisms, inoculated with a 

 non-lethal but immunising dose, are, as we have seen, ingested 

 by the phagocytes and afterwards digested within them. This intra- 

 cellular digestion is followed by the over-production of the specific 

 fixative, of which a part is excreted and passes into the plasmas. 

 These are the results of the well-established experimental data [312] 

 described in this chapter. Ehrlich's theory is in no way in oppo- 

 sition to this ; it simply attempts to penetrate more deeply into the 

 mechanism of the phenomena observed as taking place between 

 the micro-organism and the cell. The act which we simply term 

 intracellular digestion is divided by Ehrlich into its constituent parts. 

 According to him there is a combination of the fixative, on the one 

 hand, with the molecule of the micro-organism, on the other, with that 

 of the soluble ferment or cytase. According to Ehrlich it is the 

 amboceptors of the cells which become detached in order to furnish 

 the fixative that circulates in the plasmas. For us there is simply an 

 over-production of one of the two ferments of intracellular digestion, 

 without defining more exactly what constituent part of this ferment 

 passes into the circulation. The two theories may supplement each 

 other but are in no way contradictory in principle. There is only a 

 single important point wherein they do not accord. Ehrlich thinks 

 that the cytases are always free in the body fluids and that the cells, 

 in order to exert a digestive action on the micro-organisms, must 

 previously seize their molecules by means of one of the groups of their 

 amboceptors. We, on the contrary, have developed the idea that the 



