480 



BACTERIOLOGY. 



made as in the case of the toxin. Thus, if the 250 g. animal is to 

 receive 0.25 c.c. of serum B, but the one taken weighs 300 g., then, 



300 



250 : 0.25 



x = 0.30 c.c. serum B. 



The corrected amount of serum B is measured out for each 

 guinea-pig" and added to the similarly corrected amount of toxin A. 

 The mixture is then injected subcutaneously . The temperature and 

 weight should be taken, and the local effects should be observed. If a 

 given injection produces no ill effect it is evident that the amount of 

 serum injected contains at least the corresponding number of immuni- 

 ty units. It may, of course, contain a larger number. On the other 

 hand, if the animal dies, it is evident that the serum does not contain 

 as many I. U. as are represented by the dose taken. If only a local 

 swelling, or a slight scar results it indicates that the serum is nearly 

 strong enough to neutralize the toxin injected. 



The testing of an antitoxin will be rendered more clear by means 

 of the following table: 



It is evident from the above that the serum contains more than 

 286 I. U., the strength claimed. The death of No. 1 indicates that 

 the serum has less than 400 I. U. per c.c. The actual amount lies 

 between 303 and 345. 



It should be borne in mind that toxins of different 

 origin and of different age have unequal neutralizing 

 power. That is to say, the amount of serum, containing 

 one immunity unit, which has been found sufficient to 

 neutralize 100 times the minimum fatal dose of a given toxin, 

 will not necessarily neutralize 100 times the minimum fatal 

 dose of another toxin. This difference is more pronounced 

 the older the culture. Thus, a culture several weeks old 



