136 PHYSICAL CHEMISTRY IN MEDICINE. 



red process produce in their surroundings or after them 

 the antibodies of the green process,* and that these prod- 

 ucts neutralize each other physiologically, just as do toxin 

 and antitoxin, the analogy between the two phenomena 

 becomes very apparent. 



In spite of a few differences, are not the chemical phe- 

 nomena of the production of a lasting complementary 

 after-image and the formation of an antitoxin essentially 

 the same? Even in EHRLICH'S bold conception of the 

 regenerative hyperplasia of the side chains, there seems 

 to be mirrored only a part of that truth which HERING 

 grasped so deeply. 



No doubt every attempt to follow these questions 

 further soon brings us to the solid barriers of our present 

 knowledge, which do not open even to the storm of 

 physical chemistry. And if some investigators, such as 

 the followers of the energetic school, carried away by 

 physical chemistry, have believed that they had hoisted 

 their flag upon the outermost pole of biology, it has 

 always been found that this was due to a failure to dis- 

 criminate between the boundaries of the known and the 

 unknown. We have therefore learned to be satisfied 

 with having arrived at a clear conception of the problem 

 before us, just as the chemist who must first carefully 

 free an unknown substance of all its impurities before 

 he holds the pure crystal in his hands. As yet the way 



* For comparison the white-black process might better be used, because 

 this leads to black in only one direction, namely, over white to black. 

 In the case of the antibodies also we obtain the antibody only by way 

 of the toxin and not conversely. The exceptions mentioned in the 

 sentence following the one to which this note refers have to do with 

 another point which will be discussed in detail at some future time. 



