ATREPTIC IMMUNITY 253 



Pasteur's " exhaustion " theory was revived by Ehrlich in a 

 modified form, under the name of " atrepsy," to explain certain 

 cases of immunity. Thus, for a chemical poison to act, Ehrlich 

 assumes that particular receptors in the protoplasm for binding 

 the poison are necessary ; these he terms " chemo -receptors." 

 Bird -pox, virulent for both fowl and pigeon, if passed through the 

 pigeon becomes completely avirulent for the fowl. To explain 

 this Ehrlich suggests that the parasite in passing through the 

 pigeon has to assimilate substances different from those assimi- 

 lated during its passage through the fowl ; therefore that part of 

 the receptors which deals with the nutritive substances of the 

 fowl's organism is not in use during the passage through the 

 pigeon, and may become atrophied, so that on the parasite being 

 transferred back to the fowl it will not be able to thrive owing to 

 the loss of the receptors necessary to assimilate the fowl's nutri- 

 tive substances. Ehrlich suggests that the majority of non -patho- 

 genic micro-organisms, if introduced into the animal body, perish 

 by this mechanism. In the case of mouse carcinoma inoculated 

 into rats, the tumour-cells proliferate for a few days, then atrophy 

 and disappear. Ehrlich suggests that some specific substance 

 is necessary for the proliferation of mouse carcinoma-cells which 

 is not present in the rat, and as soon as the traces of this specific 

 substance carried over by the inoculation are used up, the cancer- 

 cells cease to proliferate and finally atrophy and disappear. 

 These are examples of Ehrlich' s " atrepsy " and " atreptic 

 immunity." 



Chauveau, in his retention theory, suggested that the 

 bacteria during their growth in the tissues form sub- 

 stances which ultimately inhibit their growth, and, if 

 the animal recovers, prevent a subsequent development 

 of the organism. The same objections may be urged 

 against this hypothesis as against Pasteur's exhaustion 

 hypothesis. 



Bacteriolysis and phagocytosis are probably the two 

 principal factors which bring about the refractory con- 

 dition in acquired immunity against bacteria, as well as 

 recovery from an infection. After immunisation it may 

 be shown that phagocytosis is increased, and that positive 



