G. W. McCOY 955 



one hour to allow combination to take place. The guinea pigs should be between 250 grams 

 and 300 grams in weight, and the doses of toxin and antitoxin are to be increased propor- 

 tionately to the weight for guinea pigs weighing over 250 grams. With every test of an un- 

 known antitoxin, four control guinea pigs should receive the test dose of toxin mixed with 

 the test dose (one-tenth unit) of standard antitoxin, so that the two antitoxins may be 

 accurately compared and the test dose of toxin increased if necessary in subsequent tests; 

 liquid toxins have been found to decrease gradually in toxicity. In diluting the standard 

 antitoxins, the method indicated on the label should be followed. The first dilution should 

 be made with a capacity pipette, to be washed out in the diluting fluid, on account of the 

 viscosity of the glycerinated serum. 



The units of botulism antitoxins (types B and C) are similarly definite amounts of the 

 standard types B and C antitoxins to be sent out to serum establishments which may be 

 licensed for the production of these antitoxins, the unit of each being 0.4 cc. of the glyceri- 

 nated solution. Antitoxins to be tested are compared with the standard units by means of 

 test doses of types B and C toxins, using the same method as above described for type A. 



B. Perfringens {CI. welchii) antitoxin. — This antitoxin is designed for use against 

 certain of the "gas gangrene" infections. It is standardized' in accordance with the 

 following : 



The unit shall be i cc. of the standard serum which is kept in cold storage. To estimate 

 the potency of a commercial antitoxin, the test toxin shall first be standardized by inoculat- 

 ing pigeons intramuscularly with i/ioo unit of standard serum mixed with varying amounts 

 of toxin to determine the smallest dose of toxin which will overcome this amount of serum 

 and kill the pigeon within 24 hours. This dose of toxin, called the "test dose," is usually 

 somewhat greater than 10 minimal lethal doses. The test dose of toxin is then to be mixed 

 with varying amounts of the serum to be tested and injected into a second series of pigeons; 

 that amount of serum which gives protection for 24 hours against the test dose of toxin 

 shall be considered to contain i/ioo unit. The serum-toxin mixtures are incubated 45 

 minutes at 37° C. before injection. Pigeons should weigh preferably between 325 and 375 

 grams, but the doses of toxin and antitoxin shall be proportioned to the weight, 350 grams 

 being taken as the standard weight. 



SCARLET FEVER STREPTOCOCCUS ANTITOXIN 



The unit for measuring the strength of scarlet fever streptococcus antitoxin is 

 defined as the neutralizing power possessed by a definite quantity of anti-streptococcic 

 serum preserved at the Hygienic Laboratory of the United States Public Health 

 Service under special conditions to prevent deterioration. This quantity is now 

 equivalent to ten times the amount of scarlet fever streptococcus antitoxin necessary 

 to neutralize one test dose of the corresponding toxin, each test dose containing five 

 times the amount of toxin necessary to give in the majority of non-immune indi- 

 viduals in twenty-four hours following intracutaneous injection, a skin reaction i cm. 

 or more in diameter. 



The skin-test dose was determined originally by the Drs. Dick^ for a certain lot of 

 toxin. Since that time new toxins have been standardized in comparison with the 

 original toxin or against toxins so standardized. 



' Bengtson, I. A,: Hygienic Laboratory Bull. 122. 1920. 

 'Dick, G. F., and G. H.: J.A.M.A., 84, 1477-81. 1925, 



