4S6 COLLECTED STUDIES IN IMMUNITY. 



which a given number of L. D. were contained would vary from case 

 to case, depending on the varying quantity of poison produced by 

 the bacilli. 



Closer investigations, however, showed that in reality the con- 

 ditions are entirely different, the number of L. D. contained in Lt 

 varying enormously in different toxic bouillons. In poisons which 

 have been analyzed the figures have fluctuated between 15 and 160. 

 Since it had been shown, especially by myelf, that the neutralization 

 of toxin-antitoxin rests on a chemical basis, this result could only 

 be explained by assuming that the diphtheria bouillon, in addition 

 to the toxins, contained other non-toxic substances which were able 

 to combine with antitoxin just like the diphtheria toxin. I deemed 

 it to be of the highest importance to clear up this mystery experi- 

 mental!}', and therefore subjected a number of different poisons (some 

 freshty derived, others precipitated with ammonium sulphate, and 

 still others which had been kept for a long time) to comparative 

 analyses. In the course of these it was found that the non-toxic 

 substances, which still possess combining properties, increase as the 

 toxic bouillon ages, and I therefore studied these changes in the 

 poisons genetically at various stages. 



I emphasize this part of my method because the casual remark 

 by Arrhenius and Madsen l that my results were derived mainly from 

 a study of decomposed poisons might readily be misconstrued and 

 give one the impression that in my investigations I had not been espe- 

 cially careful. I may at once add, however, that my most valuable 

 results were obtained by studying the course of this decomposition, 

 but this, of course, corresponds entirely with the methods of chem- 

 istry. It is impossible to gain an insight into the constitution of 

 highly complex combinations by means of an analysis which leads 

 only to the compact formula. This can only be gained by the 

 careful decomposition of the substance to be studied. Whatever 

 knowledge we possess regarding the constitution of sugars, uric acid 

 derivatives, alkaloids, etc., is due mainly to the decompositions intel- 

 ligently carried out, and a careful study of their products. Of course, 

 the decomposition must not give rise to secondary reactions which 

 could obscure the results ; this might be the case if strong acids or a 

 high temperature were employed. The decomposition must be 

 quantitative and of moderate intensity. The following observa- 

 tions will show that this is especially the case in the spontaneous 



'I.e. 



