ANTITOXIN. 7 



the antitoxic condition of the blood. This latter is esti- 

 mated and tested by Behring and also by Roux by the 

 neutralising action it possesses on diphtheria toxin. A 

 toxin is prepared of a given strength — determined by the 

 amount required to kill within thirty hours a given weight 

 of guinea-pigs — of this a tenfold fatal dose is injected into 

 each of a series of guinea-pigs, and subsequently, about six 

 hours later, a definite amount of antitoxin serum is injected 

 into each animal ; that serum which in a given dose is capable 

 of neutralising the toxin, i.e., capable of preserving the 

 animal, is evidently of higher potency than the serum of 

 which a larger dose is required ; or the serum of which a 

 given quantity can neutralise a larger amount of toxin is of 

 higher potency. Now, as regards the application of such 

 standards to the use of the antitoxin serum in the treatment 

 of diphtheria in the human subject, it must at the outset be 

 confessed that there is little to guide us in the matter, for 

 in a case of human diphtheria, in which the serum is to be 

 used, the amount of toxin circulating in the body is an alto- 

 gether unknown quantity ; whether comparatively or abso- 

 lutely it is as great or greater than a tenfold fatal dose in the 

 guinea-pigs of a given weight, whether it is greater in a 

 severe case than in a mild case of diphtheria, are matters 

 about which no data exist. All that can be said is that the 

 greater the antitoxic potency of the injected serum, the more 

 likely is it that it will be capable of neutralising the toxin 

 already formed, or likely to be formed, by the still active 

 diphtheria bacilli. 



There is one aspect of the subject which requires 

 consideration, and which in the methods of production of 

 antitoxin by Behring and by Roux does not seem to have 

 been sufficiently taken account of. It is this : under 

 natural conditions, when an animal or human being- has 

 passed through one attack of an infectious disease and has 

 thereby acquired resistance amounting in some instances to 

 an almost complete immunity, this condition of resistance 

 or immunity is brought about by the activity of the specific 

 microbes ; these during their life and multiplication in the 

 infected body eventually cause the accumulation of the 

 specific antitoxins in the blood and tissues. Now, the 



