THE CONSTITUENTS OF DIPHTHERIA TOXIN 489 



Naturally the poisons whose toxophore groups are very labile 

 will be the least pure. This is especially true in tetanus poison, 

 which is far more readily destroyed than diphtheria poison. In the 

 former, several hours' standing of an aqueous solution suffices to give 

 rise to toxoid formation. It is all the more probable, therefore, 

 that the toxin produced in the usual manner by keeping the culture 

 in the incubator for eight days contains a considerable admixture of 

 toxoids. In the precipitation with ammonium sulphate these tox- 

 oids, of course, are present in the resulting solid product. 



A dry poison of this kind, such as I placed at Madsen's disposal 

 for his experiments, can, of course, keep for a long time unchanged 

 provided it is carefully preserved; the primary content of toxoid, 

 however, also remains unchanged. 



For this reason I believe that the assumption of Arrhenius and 

 Madsen, that the tetanus poison used by them was a pure poison, 

 since it did not change, is entirely unwarranted. It is even possible 

 that this particular specimen contained far more toxoids than the 

 old toxin solutions which I had employed. 



In pure chemistry in carrying out exact mathematical determina- 

 tions it is a general principle that the substance be either absolutely 

 pure or at least that its degree of purity be exactly determined by 

 analysis. In determining the molecular weight of an element, a great 

 deal of preliminary work (recrystallization, etc.) is required in order 

 to obtain the original material as pure as possible. If this cannot 

 be done, as, for example, in the case of hydrogen peroxide, or ozone, 

 a quantitative study requires at least that the exact percentage of 

 pure substance contained in the mixture be known. It is hardly 

 necessary to say that these principles should, as far as possible, be 

 applied to the study of toxins. In these substances also one should 

 know the degree of purity before attempting any exact investigations 

 Lut just in this domain, where it is impossible to isolate the substances, 

 this task is uncommonly difficult. It required a year's most tiresome 

 and monotonous labor before I was able, by means of very exact deter- 

 minations of all kinds of poisons, to approach this problem. At that 



produced in a very short time (three to four days in the incubator) are not free from 

 toxoids. In one such poison (No. 9 of the titration series) I found 123 L. D. 

 in L t . I was therefore greatly pleased recently to hear from Dr. Louis Martin, 

 who has had such wide experiences in this direction at the Pasteur Institute, 

 that in his fresh poisons he never saw the figure 200 L. D. in Lf reached. 



