220 CLINICAL BACTERIOLOGY. 



duced the abbreviation DTN 1 , and he designates a toxin of 

 I o times this strength as DTN 10 and one of T ^- this 

 strength as 2j~ As guinea-pigs weighing 250 grams are 

 not always obtainable, the important minimal lethal dose is 

 not estimated with regard to the entire experimental ani- 

 mal, but upon the basis of each gram of living bodily 

 weight. In order to express this relation also in simple 

 symbols Behring designates the whole animal with an m,* 

 and a gram of the living bodily weight with an M. The 

 weight of the guinea-pig in each individual instance is 

 added besides, and above the letter m (thus, for instance, 

 m 280 stands for an animal weighing 280 grams). The 

 minimal lethal dose for i gram of body-weight thus, for 

 I M is indicated by prefixing the symbol -f-. + I5OOM 

 expresses that amount of toxin that just suffices to destroy 

 6 guinea-pigs each weighing 2 50 grams. One cubic centi- 

 meter of DTN 1 causes the death of 100 m 250 , and is thus 

 equal to +25,000 M that is, it rep resents 25,000 minimal 

 lethal doses for each gram of living guinea-pig by weight. 

 Of diphtheria-toxin 10 times the normal strength, DTN 10 , 

 i cu. cm. == + 250,000 M; I cu. cm. of diphtheria-toxin 

 one-tenth the normal strength, ^^, =-\- 2500 M. 



In order to obtain an active diphtheria-toxin it is ob- 

 viously necessary to employ highly virulent diphtheria- 

 bacilli in preparing the bouillon-cultures. As a consequence 

 it is frequently necessary to fortify the virulence of the 

 diphtheria-bacilli. A diphtheria-bacillus that has com- 

 pletely lost its property of generating toxin can not be 

 rendered virulent again by any method thus far known. 

 If, however, a trace of virulence remain, this may be 

 augmented by repeated passage through animals. Six or 

 eight hours after the injection a specimen is obtained from 

 the area of local edema, and with it a culture is made, which 

 then serves for the inoculation of a new animal. Roux 

 and Yersin augmented and accelerated the production of 

 toxin on the part of the diphtheria-bacilli by cultivating these 

 in a shallow layer of bouillon through which a current of 

 moist air was constantly passed. The diphtheria-bacillus 

 thrives vigorously in nutrient media containing sugar, 

 although it generates considerably less toxin. 



*In the original, the German capital letter 9Ji is employed, but for conve- 

 nience sake the English small letter m is here substituted. A. A. E. 



