142 VETERINARY BACTERIOLOGY 



of fresh antitoxin. A series of syringe tubes, each containing one 

 L-f dose of the toxin, is arranged, and the varying amounts of 

 the antitoxin serum to be tested are added. The amount of 

 serum which will prevent a 250-gm. guinea-pig from dying in 

 less than four days contains 1 immunity unit. 



According to Ehrlich, diphtheria toxin is in reality made up of 

 two poisons the true toxin and toxone. The latter he holds to 

 account for the paralyses that are frequent sequelae in diphtheria. 

 The same antitoxin neutralizes both the toxin and the toxone. 

 This toxone is of some theoretic and practical importance in the 

 standardization of the toxin and the antitoxin. 



The amount of antitoxin present varies greatly in the serum 

 produced by different horses. One which contains less than 

 250 U. I. per cubic centimeter is rarely used. The greater the 

 concentration, the more valuable is the serum for prophylaxis and 

 cure. Many efforts to concentrate diphtheria antitoxin have been 

 made, all based upon the fact that the blood-serum is a mixture of 

 various proteins, and that the antitoxin seems to be inseparably 

 bound up with certain ones only of these. The removal of the 

 proteins having no antitoxic value results in a considerable con- 

 centration of the antitoxin-holding proteins. Several methods 

 have been devised for this purpose. All are based upon differences 

 in solubility or coagulability of the various serum constituents. 

 The methods of Gibson and of Banzhaf deserve mention. The 

 former precipitates the serum by the addition of an equal amount 

 of a saturated solution of ammonium sulphate. This precipitates 

 the antitoxic and some other fractions of the serum, but does not 

 precipitate certain of the non-antitoxic albumins. These are 

 filtered out, the precipitate is dissolved in water to its original 

 volume, and is again precipitated by ammonium sulphate. This 

 precipitate, when filtered, is relatively free from albumins. It 

 is then stirred into a saturated solution of sodium chlorid, which 

 dissolves the pseudoglobulins with the antitoxin. The insoluble 

 portions are filtered out and the clear filtrate acidified by the 

 addition of 0.25 per cent, of 80 per cent, acetic acid. The pre- 

 cipitate which is thrown down is collected over hard filters, par- 

 tially dried by pressure with bibulous filter-paper, and placed in a 

 parchment bag for dialysis in running water. The acid is neu- 



