S8 THE AMERICAN MONTHLY [Feb. 



accurately determined by injections of various amounts 

 of toxin into a number of guinea pigs, the smallest 

 amount of toxin that invariably causes the death of the 

 control animal in a reasonable time being regarded as the 

 minimum fatal dose. It is usually calculated so much 

 per 100 gm. body weight. 



Every lot of antitoxin is carefully tested, and if the con- 

 trol animal shows evidences of cedema at site of injection, 

 or diminution in body weight, the antitoxin is rejected. 



A page from the laboratory minutes shows this deter- 

 mination of strength. Having found the minimum fatal 

 dose here used to be 0.005 per gram weight of guinea pig, 

 the control animals are given ten times this absolutely 

 fatal dose of diphtlieria toxin or poison, and if testing 

 for 100 units per ccm., as appears from experiment on 

 animal No. 1,080, 1-iOOO ccm. antitoxin obtained from 

 horse No. 109 H is given; if testing for 250 units per 

 ccm., 1-2500 ccm. of antitoxin is given; if for 500 units, 

 1-5000 ccm. of antitoxin would be administered. 



Tests for 500 units are shown on control animal 1,070 

 and for 350 units on control animal 1,076. 



While this paper does not deal with the therapeutic 

 value of diphtheria antitoxin, the absolute scientific value 

 and correctness of these tests may be appreciated by 

 these observations, and we prove the theraj)eutic appli- 

 cation of the antitoxin by its neutralizing or protective 

 value upon the control animals receiving ten times the 

 amount of toxin that always kills. Unfortunately, we 

 cannot thus arrive at the dose for therapeutic application 

 since the human subject is much more susceptible to the 

 poison, and we have no possible means of determining 

 the amount of toxin secreted by the diphtheria bacilli in 

 the patient suffering with diphtheria. 



Appreciating, however, that the only effect of diphthe- 

 ria antitoxin is in neutralizing the toxins of diphtheria, 

 we know how necessary it is to make application of this 



