TOXIN AND ANTITOXIN. 519 



are usually given for various animal species. In the beginning it 

 was thought that the same conditions held true for the bacterial 

 poisons and several such scales of toxicity were given out by high 

 authorities. As soon, however, as different toxin solutions of the 

 same species were examined, e.g. diphtheria toxins obtained from 

 different cultures or in different laboratories, it was found that, 

 unlike the alkaloids, the scale of toxicity was a variable one. In 

 the case of one poison, for example, I found that a guinea-pig of 

 250 grammes was uniformly killed by a dose of 0.00375-0.004 cc., 

 and a rabbit of 1800 grammes by a dose of 0.009 cc. This corre- 

 sponds to a ratio of 1:2:2-2.4. In another poison the figures were 

 0.003 for guinea-pigs and 0.004 for rabbits, corresponding to a pro- 

 portion of 1:1.3. This showed that in two different poisons the 

 susceptibility of rabbits varied more than half. 



The conditions, however, are far more interesting and instruc- 

 tive in the case of tetanus poison. For a long time a controversy 

 existed between v. Behring and Tizzoni. The former stated that 

 tetanus poisons act 150 times weaker on rabbits than on mice, whereas 

 Tizzoni declared that a poison prepared by him was just as toxic 

 for rabbits as for mice. From the papers of these authors it is cer- 

 tain that the tw r o poisons when tested on mice were identical. A 

 definite amount of either poison for example, a single fatal dose 

 for mice was neutralized by the same quantity of antitoxin. So 

 far as mice were concerned, therefore, the two poisons were identical. 

 As soon as the poisons were tested on rabbits, however, the above- 

 mentioned enormous difference in toxicity becomes apparent. This 

 at once shows that these two poisons cannot possibly be identical. 

 Wherein, then, does the difference consist? We have seen that the 

 two poisons are neutralized by the same antitoxin, and that fur- 

 thermore immunization with one of the poisons is followed by the 

 production of an antitoxin, which acts also on the other poison. 

 From this it follows that the haptophore group must be the same 

 in both. Hence we must be dealing with a difference in the toxo- 

 phore group, v. Berhing's poison possessing a toxophore group which 

 is highly virulent for mice and only slightly so for rabbits, whereas 

 Tizzoni's poison contains a group which acts equally on both ani- 

 mals. This difference would be very like that which I have demon- 

 strated in the case of diphtheria toxin and toxon. One might, how- 

 ever, think of an entirely different explanation, namely, that the 

 strain of bacteria with which Tizzoni worked secreted an entirely 



