402 COLLECTED STUDIES IN IMMUNITY 



a temporary, metabolic product. Perhaps this can be brought into 

 connection with the interesting observation of Gley that the blood- 

 celJs of new-born rabbits are highly resistant against eel poison, 

 acquiring the normal high susceptibility only in the course of 

 weeks. 



Be this as it may, everything indicates that there is an organic 

 harmonious connection between the metabolism of any given period 

 and the nature of the receptors present. This connection depends on 

 the fact that substances with haptophore groups exert a stimulus 

 on the protoplasm which excites the production of the receptors in 

 question. 



In conclusion I wish to point out that many facts indicate that 

 the species of receptors found in the erythrocytes may also be present 

 in the cells of other organs. Thus, mentioning only one example, 

 tetanolysin is anchored not only by the erythrocytes, but also by 

 the brain and other organs. This phenomenon also shows itself in 

 the immunizing test. Von Dungern, for example, found that serum 

 of rabbits which had been treated with tracheal epithelium of oxen 

 exerted a marked haemolytic action on ox blood in addition to its 

 injurious action on epithelium. Metchnikoffs objection that this 

 was due to an error in technique (the injection of admixed blood- 

 cells) was controverted by von Dungern, who showed that injections 

 of cow milk, a material absolutely free from blood-cells, produced 

 the same hsemolysins. It follows that certain receptors must be 

 common to the red blood-cells and the epithelial tissue or the milk 

 derived from this. 



The wide distribution of a particular combining group harmonizes 

 very well with the assumption discussed above concerning the func- 

 tions of the receptor apparatus of the red blood-cells. 



According to Miescher's comparison the red blood-cells serve as 

 a sort of bank of deposit where the metabolic products in excess at 

 any given time may be stored temporarily. In this case the sub- 

 stances will be yielded up only to organs possessing suitable receptors. 

 This process will be all the more complete if the affinity of the tissue 

 receptors is greater than that of the blood receptors. There are 

 many reasons for believing that the affinity of the tissue receptors 

 is not constant, and that it can be considerably increased through 

 certain stimuli (assimilative stimuli). It is obvious that hunger, if 

 we may apply the term to purely cellular processes, must constitute 

 one of the most important assimilative stimuli. This functional in- 



