498 STUDIES IN IMMUNITY. 



which in their character and cellular appearance resemble but are 

 not completely identical with pre-existent principles. These new 

 substances, as a result of elaboration and change, have become 

 endowed with special properties, notably a more marked affinity 

 for the specific antigen in question. In view of the wonderful 

 faculty of adaptation of organisms and their inexhaustible resources, 

 in view, for example, of what one sees (as Landsteiner and Reich 

 have done) in Oscillaria that have been submitted to the influence 

 of certain luminous rays and which take specifically the comple- 

 mentary color to that possessed by these rays (Engelman and 

 Gaidukow), such an hypothesis would be in no way irrational. 

 Both conceptions, then, are a priori equally possible to defend. 

 Why should we choose one of them and condemn the other before 

 awaiting the result of experimentation? Such solutions given 

 prematurely to obscure problems are all the more useless, as with 

 all their apparent detail they fail to answer definite important 

 questions. In fact these over-produced receptors are but vague 

 names. Where are they to be found? Are they, before immuni- 

 zation, enclosed within cell protoplasm or do they swim freely in the 

 blood? More exactly, we are aware that in the blood of normal 

 animals there are normal antibodies, the protecting power of which 

 is in general slight but nevertheless detectable, such substances as 

 agglutinins, sensitizers and even antitoxins. It is just as logical to 

 suppose that bacteria or poisons, when injected into a normal 

 animal, react with these normal antibodies. Are these normal 

 antibodies really the same receptors which are subsequently over- 

 produced to form the specific antibody that is characteristic of the 

 immunity that has been acquired? Or are the receptors in whom 

 this function resides other than the normal antibodies which are 

 present in the blood; should we, in other words, seek for them in 

 the protoplasm of the nerve cell, for instance, when dealing with 

 diphtheria toxin? Ehrlich's theory, to be sure, harmonizes with 

 either alternative, but it would scarcely seem that it is ever indica- 

 ted which of the two should be accepted. 



In certain other respects Ehrlich's theory has apparently been 

 more precise. It attempted, at a stage when the data were still very 

 limited, to interpret the mode of action of antibodies with antigens, 

 here it seems to me that it has exercised a perturbing influence on 



