of concentration that destroys or paralyzes untrained cells of the same kinds. When Pasteur for his first inoculation for the cure of rabies uses materials from an old desiccated cord, the essentials of his injection are not "waste products," but extremely attenuated toxins—toxins so attenuated that the phagocytes, far from being destroyed or paralyzed, react in response to the stimulation from them, and are thereby placed in a position of such advantage, that instead of being destroyed they are able to react in a similar manner to the stimulation of the more virulent toxins and the microbes producing them of the next inoculation, whereby they attain a position of still greater advantage, and are able to withstand and react do the stimulation of the toxins of the third injection, and so on in succession till the toxins of the most virulent injection, which would otherwise have destroyed or paralyzed them, to which they could not have reacted at one effort, produce no other effect than another reaction of like kind, by virtue of which they are able to withstand those toxins, and to attack and destroy the micro-organisms that produce them. Rabies, as we know, is of slow development in man—i.e. the microbes increase slowly in him, or at the. least they produce their toxins slowly in him, one or both, for it is not till weeks or months after infection that he exhibits the characteristic symptoms of the disease. This long incubation period renders possible the success of the scientist in his endeavours to save life—affords time during which he is able to train the phagocytes to successful battle.
Syphilis resembles rabies in its slow development, and therefore as regards it also we may hope or expect that means will be found of attenuating the virus, perhaps by passing it through a series of resistant animals, or better still, by subjecting a pure culture, if
