DIPHTHERIA BACILLUS. 369 



matter with new and similar substance; after the stimuli 

 following several repeated losses and replacements of 

 this substance the cells produce it in excess. This sub- 

 stance, whether originally in the normal cell or repro- 

 duced there, and whether remaining in the cell or 

 thrown out into the circulation, is antitoxin. 



The above summary merely gives an outline of 

 some of the points in Ehrlich' s most interesting article. 

 To become fully acquainted with the reason for his 

 theories the article itself must be carefully read. 



Interest in both his theoretical reasoning and in his 

 practical conclusions led us to subject both to a series 

 of tests which have, I believe, added some interesting 

 facts to those already published by Ehrlich as well as 

 cast doubts on some of his conclusions. 



The results of these experiments of Atkinson and 

 myself * were fully in accord with those published by 

 Ehrlich as to the varying neutralizing value of a 

 minimal fatal dose of "toxin"; they, however, also 

 indicate roughly a general law in accordance with which 

 these changes occur. 



The neutralizing value of a fatal dose of toxin is at 

 its lowest in the culture fluid when the first consider- 

 able amounts of toxin have been produced. After a 

 short period, during which the quantity of toxin in the 

 fluid is increasing, the neutralizing value of the fatal dose 

 begins to increase, at first rapidly, then more slowly. 



While the culture is still in vigorous growth and new 

 toxin is being produced, the neutralizing value of the 

 fatal dose fluctuates somewhat, but with a generally 

 upward tendency. After the cessation of toxin pro- 



1 Journal of Experimental Medicine, vol. Hi., No. 4. 

 24 



