DIPHTHERIA. 225 



The total of toxoids, toxins, and epitoxoids, equals, 

 according to Ehrlich, 200 ; a toxin possessing the a 

 equivalent of toxin and z-epitoxoid should yield the following 

 formula : (200 z) toxoids -f- toxin -(- z-epitoxoids. 

 To this the immunity-unit is added, and in this way is ob- 

 tained the value L = (2OO--z) toxoid-antitoxin -|- a. 

 toxin -antitoxin -J- z-epitoxoid-antitoxin. The value of L + 

 is obtained by adding to the neutral mixture so much 

 of the original material that the z-epitoxoid-antitoxin is 

 decomposed by the mixture of toxoid -f- toxin. As is 

 evident, this addition must represent a. 20 ^_ z toxin-units. The 

 epitoxoid toxin-units have just been found to be ft = D i. 

 It results that y5 = -^z^ and z = -^|. If the amount of 

 epitoxoid is estimated according to this formula, figures are 

 obtained that stand in the simplest relation to that found 

 for the number of immunity-units, 200 namely, j, ^, 

 i^,' or i^, or Y* thereof. 



As the outcome of these experiences, Ehrlich has sug- 

 gested the following alterations in the directions for testing 

 the diphtheria-antitoxin, and these have been confirmed 

 by a decree dated March 29, 1897 : 



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

 antitoxin-powder of accurately determined strength, pro- 

 tected against the influence of oxygen and water, is em- 

 ployed. This is contained in carefully measured quantities 

 in specially prepared vacuum-tubes. The apparatus at 

 the time present in the laboratory 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 contents of a tube are 

 dissolved in 200 cu. 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 in- 

 stance, in I cu. cm. of a -^ 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 



