458 



INFECTION AND RESISTANCE 



In the above tables, according to our previous definition of the 

 antitoxin unit, the serum would contain 900 units to the cubic centi- 

 meter, since 1/900 c. c., injected together with the L+ dose of the 

 standard toxin, resulted in the death of the guinea pig in four days. 

 In order to allow a margin of safety Rosenau and others have sug- 

 gested that the unit should be determined, not by the quantity of 

 antitoxin, which delays death by the L + dose for four days, but 

 rather by the quantity which, with the L + dose, results in saving 

 the life of the guinea pig. According to this latter standard the 

 serum employed in the table would be spoken of as containing 700 

 units to the cubic centimeter. Of course the tabulated measurements 



run MM 



BATTERY OF ROSENAU SYRINGES PREPARED FOR ANTITOXIN STANDARDIZATION. 

 (Taken from Rosenau, U. S. Hygienic Bulletin 21, 1905.) 



are rough, leaving an undetermined zone of 100 units. The exact 

 number of units to the cubic centimeter could, of course, be deter- 

 mined with greater accuracy by now carrying out another series of 

 tests in which the amount of serum varied between 1/700 and 1/900 

 of a cubic centimeter. 



In carrying out such a standardization the toxin is diluted so 

 that the L + dose is contained in 2 c. c. This can easily be done. 

 For instance, in the above the L + dose being 0.29, it merely necessi- 

 tates adding to each 0.29 c. c. of toxin 1.71 c. c. of salt solution, 

 to each 2.9 c. c., 17.1 c. c. The antitoxin also is made up in such a 

 way that the required dilution is contained in two cubic centimeters, 

 since a total volume of 4 c. c. has been agreed upon as standard for 

 these tests, the injected volume having much influence upon the speed 

 of absorption. In using the so-called Rosenau syringe, shown in the 

 figure for the standardization of antitoxin, the antitoxin is made up 

 to 1 c. c. in each case, so that 1 c. c. of salt solution may be added to 

 wash out the syringe after injection of the mixture. The mixtures 



