72 BACTERIAL POISONS OF INFECTIOUS DISEASES. 



float away in the blood, constituting the antitoxin. Moreover, the 

 atomic group or side-chain, after being liberated from the cell, may 

 possibly acquire greater avidity for combination with the toxin ; or, 

 in other words, the toxin will combine more readily with these side- 

 chains when free and floating in the blood than when they constitute 

 parts of the molecules of the cells. 



3. The diphtheria toxin, as it exists in sterilized cultures, is com- 

 posed of equal parts of toxin and toxon. The toxon, which accord- 

 ing to this theory is supposed to exist in the diphtheria culture, is 

 believed to be without any serious efiect upon animals. It may 

 cause local oedema, but never kills. Ehrlich's theory supposes that 

 the toxon, which we may regard as inert, has quantitatively the same 

 power of combination with antitoxin as is possessed by the toxin, 

 but combines with the antitoxin with less avidity. In order to 

 understand why the theory provides for the existence of toxin and 

 toxon in equal quantities in the diphtheria culture, we will use cer- 

 tain formulas proposed by Ehrlich : 



T= the minimum fatal dose of the toxin (a quantity sure to kill 

 a guinea-pig of 250 grams weight within five or six days). 



/= one immunity unit which is capable of neutralizing the effects 

 of 100 T. 



Now, if I be mixed with 100 7 and injected into an animal, no 

 ill effect results. If the toxin were a simple body, I plus 100 T 

 plus T should kill one animal. But experimentally we find that 

 this amount has no effect, and must be greatly increased before there 

 is enough free toxin in the mixture to kill. Ehrlich represents the 

 quantity of poison necessary to neutralize I by ij. Then I plus L^ 

 is a mixture which contains neither free toxin nor free antitoxin and 

 is wholly without effect upon animals. By L^ he indicates the quan- 

 tity of poison which must be added to Zin order to kill a guinea-pig 

 of 250 grams weight within five or six days. Let us suppose that 

 in a given culture T= 0.01 c.c, then J= 1.00 c.c. = 100 T. L^ = 

 1.00 c.c. = 100 T. Now, if this were a poison like strychnia we 

 would expect that L_^. = 1.01 c.c. = 101 T, would kill, but in reality, 

 as has been stated, we find that we have to add more of the toxin to 

 L^ in order to produce fatal results with the mixture, and we have 

 theoretically the following : 



T= 0.01 c.c. 



i+ = 2.01 c.c. = 201 T. 



■L p = 1.00 c.c. = 100 T. 



lb = 1.01 c.c. = 101 T. 



As here figured out, Ehrlich's theory which provides for the ex- 

 istence in the crude toxin of equal parts of toxin and toxon, is the 

 only possible explanation. In L^ both toxin and toxon are fully 



