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PHARMACEUTICAL BACTERIOLOGY. 



mined experimentally), and a graded amount of the serum to be standard- 

 ized/so that the first tube has, in all probability, not enough antitoxin to 

 neutralize the one hundred fatal doses of the toxin, and the eighth tube has, 

 in all probability, a great excess of antitoxin. The contents of one tube is 

 injected into a guinea-pig, thus requiring eight pigs. The animals are 

 marked and kept under close observation. The first, second and perhaps 

 third die, showing that not enough serum was added to neutralize the toxin. 

 The fourth pig just recovers, showing that the amount of serum added to the 

 fourth tube was sufficient to neutralize one hundred fatal doses of the toxin. 



FIG. 59. Guinea-pigs in wire cages. These lively little animals are used in testing the 

 virulense of the diphtheria toxin which is injected into the horse and also for the purpose 

 of standardizing the antitoxin. The reasons why these animals are preferred are wholly 

 biological and physiological. They propagate rapidily, are easily kept, easily handled, 

 and respond (biologically) to the tests applied. 



This amount of serum (antitoxic) represents one unit. From this amount 

 or unit the quantities to be put into the containers are determined. 500, 

 1000, 2500 and 5000 unit quantities are put up, for the convenience of 

 physicians. 500 units constitute an immunizing dose, given to those who 

 do not have diphtheria, but who have been exposed to the disease. The 

 larger doses are curative. The rule is to give large doses, repeated as often 

 as may be necessary. 



