416 PATHOGENIC BACTERIA. 



a standard unit of antitoxin by which it may be deter- 

 mined, and to this end Ehrlich has suggested the follow- 

 ing alterations in the directions for testing the diphtheria- 

 antitoxin. These alterations have been confirmed in 

 Germany by a decree of March 29, 1897. l 



I. As a standard for the estimation of the antitoxin an anti- 

 toxin-powder of accurately determined strength, protected against 

 the influence of oxygen and water, is employed. This is con- 

 tained in carefully measured quantities in especially prepared 

 vacuum-tubes. The apparatus at the time present in the labora- 

 tory are filled each with 2 grams of a dry antitoxin 1700 times the 

 normal strength. 



II. To secure the greatest possible degree of permanence the 

 antitoxin should be dissolved in a mixture of equal parts of 10 

 per cent, solution of sodium chlorid and glycerin. A tube is to 

 be opened every three months and a new solution prepared. Of 

 the dry antitoxin at the time preserved in the laboratory, the con- 

 tents of a tube are dissolved in 200 c.cm. of the mixture 

 described, and thus a test antitoxin-solution 17 times the normal 

 strength is prepared. 



III. The present test-dose of toxin is determined with the aid 

 of an immunity-unit, such as is contained, for instance, in 1 

 c.cm. of a T ' T dilution of the test-antitoxin 17 times the normal 

 strength. To this amount of antitoxin increasing amounts of 

 toxin are added, and by means of most careful experimental 

 observations the limit is determined at which just that excess of 

 toxin becomes manifest which causes death of the animal in the 

 first four days. The amount of toxin thus obtained represents the 

 immediate test-dose. By means of the same dose of serum, for 

 the more exact characterization of the toxin, the determination of 

 a second limit is made, for the purpose of learning the dose of 

 toxin that is just neutralized by admixture with the amount of 

 serum named. 



IV. The determination of the strength of a diphtheria-antitoxin 

 is made by means of the test-dose of toxin as follows : The test- 

 dose of toxin in question — for instance, 0.355 c.cm. of tested 

 toxin at the time present in the laboratory — is mixed with 4 

 c.cm. of antitoxin corresponding to the test figures given. As the 

 test-dose of toxin is estimated for 1 c.cm. of antitoxin of normal 

 strength, or for 4 c.cm. of antitoxin yi the normal strength, an 

 antitoxin of x strength will have to be diluted % x, and in test 1 

 ing an antitoxin 100 times the normal strength, ¥ ^. 



1 See Levy and Klemperer's Clinical Bacteriology, translated by A. A. 

 Eshner, Philadelphia, 1900. 



