1896 THE MICROSCOPE. 185 



as described later under tlie testing of antitoxin, are fav- 

 orable, tbe horse is bled a large quantity, the blood being 

 collected in sterile bottles, and placed in a refrigerating 

 room for a sufficient time (about 24 hours) until tlie 

 coagulatiim allows the clear serum, which contains the 

 antitoxin, to sejtarate. This serum is drawn otf by pip- 

 ettes and preserved by the addition of 0.5 per cent trik- 

 resol. 



The most important step now awaits the operator, the 

 determination of the exact strength possessed by the an- 

 titoxin, as expressed in immunizing units. 



For this purf)Ose the minimum fatal dose of a strong 

 toxin is accurately determined by the injection of vai-ious 

 amounts into a number of guinea pigs; the smallest 

 amount of toxin that invarial>iy causes death of tlie ani- 

 mal in a reasonable lime being regarded as the minimum 

 fatal dose. It is usually calculated, so much per 100 

 grams body weight. 



A page from the laboratory record shows this deter- 

 rainalioaof strength, having found the minimum fatal dose 

 of the toxin used to be .005 per 100 gram guinea pig, the 

 control animals are given ten times this absolutely fatal 

 dose of diphtheria toxin, per 3 00 grams weight and if 

 testing for 100 units per ccm. as appears from experiment 

 on control animal 1030,1-1000 ccm. antitoxin obtained from 

 horse 109 11 is given. If testing for 250 units per ccm. 

 1-2500 ccm. of antitoxin would be given; if for 500 units 

 1-5000 ccm. of antit.txin would be administered. 



Tests for 500 units are shown on control animal 1070 

 for 350 units on control animal 1076. 



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 the 

 observations, and we prove the a})plication of the anti- 

 toxin by its neutralizing or protective value upon the ani- 

 mals receiving ten times the absolutely fatal amount of 



