THE RECEPTOR APPARATUS OF THE RED BLOOD-CELLS. 397 



to bind tetanus poison. In virtue of such an excess of tetanus 

 receptors, the brain also absorbs a considerable multiple of the L.D. 

 Hence in test-tube experiments it is still possible to neutralize con- 

 siderable quantities of poison with the brain of a guinea-pig which 

 has died of tetanus. 



All of these tacts lead to the conception that the red blood-cells 

 possess an enormous number of receptors which probably belong 

 to hundreds of different types. Of these, again, a few may be present 

 in relatively large quantities. This fact is surprising; for in a way 

 it is opposed to the view held until now concerning the function 

 of the red blood-cells. It is inconceivable that the simple inter- 

 change of oxygen, a purely chemical function of the haemoglobin, 

 would require so complex an arrangement as that just described. 

 In my opinion, therefore, this enormous apparatus indicates that 

 the red blood-cells actually exercise properties which we have thus 

 far overlooked. If we consider that the receptors in general serve 

 to take up foodstuffs, or in some cases the products of internal 

 metabolism, we may easily assume that the receptor apparatus of 

 the erythrocytes fulfills this same purpose. Since, however, we 

 know that the vita propria of the blood-cells is very limited, we 

 shall have to assume that the substances taken up are not for the 

 blood-cells' own consumption, but are designed to be given off to 

 other organs. The red blood-cells may therefore be regarded as 

 storage reservoirs in the sense that they temporarily take up the 

 most varied substances derived from the food or from the internal 

 metabolism, provided these substances are supplied with haptophore 

 groups. I may be permitted to call attention to the fact that the 

 erythrocytes contain chiefly receptors of the first order, 1 i.e., recep- 

 tors which take up substances but do not further digest them. 



After these explanations I feel justified in believing that the 

 study of receptors has opened up a new and important field of bio- 

 logical investigation. In order to make my meaning clearer I should 

 like to quote the following paragraph from Verworn (Beitrage zur 

 Physiologic des central Nerven-Systems, I. Thiel, page 68) in which 

 our present knowledge is reviewed: "The living substance of every 

 cell, so long as it actually is living and manifests vital phenomena, 

 is constantly decomposing automatically and constantly forming 

 new substances. Dissimilation and assimilation are the fundamental 



' See note, page 392. 



