THE RECEPTOR APPARATUS OF THE RED BLOOD-CELLS. 401 



tible after several weeks, and further that in this case there had 

 been a disappearance of the special receptors previously demon- 

 strated as present. We have also encountered the reverse of this, 

 namely, the appearance of receptors previously absent. 



Evidently this coming and going of certain receptors reflects 

 internal metabolic processes which may be dependent on a large 

 number of external or internal factors. In this connection a fact 

 observed by Kossel is especially interesting. This observer found 

 that during the course 1 of immunization with eel blood the blood- 

 cells of rabbits acquire a high degree of resistance against the poison, 

 a fact which we should perhaps ascribe to a lack of receptors. In 

 this case we are dealing with something which is specific for the 

 immunization with eel blood, for we could not obtain these results 

 with two other blood poisons, crotin and tetanolysin. 



To a certain extent the experiments of Kossel, Gley, and Tschis- 

 towitsch furnish a clue to the mechanism of these phenomena. They 

 show that the first phase of immunization is that of antitoxin 

 formation, and that the unsusceptibility of the red blood-cells is 

 not developed until later. 



The way in which blood-cells which have previously been sus- 

 ceptible to a certain poison become unsusceptible to this can very 

 readily be explained. We have seen that those blood-cells, which 

 are susceptible to the action of a poison (e.g., eel blood) possess 

 appropriate receptors. Under physiological conditions the office of 

 these is to anchor a certain particular product of metabolism, .r. If 

 now through treatment with the poison the specific antitoxin is 

 produced, it is clear that this antitoxin when present in the circu- 

 lation is able to anchor not only the poison but also the normal meta- 

 bolic product, x, thus preventing the latter from combining with the 

 erythrocytes. Since this, however, renders the corresponding recep- 

 tors permanently useless, the possibility of their disappearance is at 

 once given after the manner of atrophy through disuse. This will 

 occur most readily in those cases in which the substance x can 

 readily be spared by the cell, i.e., cases in which (as in sugar) 

 the substance can be replaced by some other, kind of material 

 (e.g., fat). 



A disappearance of the receptors can, however, occur without 

 the development of such a deflecting antibody, as is shown by the 

 isolysin experiments. The most natural conclusion is that the lack 

 of receptors in this case is produced by an inconstant, perhaps only 



