CHEMISTRY OF ANTITOXINS 141 



Atkinson l attempted to determine the proteid nature of anti- 

 toxin by the biological method (i. e., by means of the precipitin 

 reaction). He immunized rabbits with globulin obtained from 

 normal horse serum and with globulin from antitoxic serum, 

 and in either case obtained a serum precipitating the globulin 

 of antitoxic serum, and with it all the antitoxin. This experi- 

 ment merely shows that the antitoxin is carried down with the 

 globulin precipitates and does not prove that it is itself a globu- 

 lin. When the precipitating serum was added to a neutral 

 mixture of toxin and antitoxin, it did not separate the antitoxin 

 from the toxin and leave the latter free, indicating that the 

 toxin-antitoxin union is quite firm. 



The relation of antitoxins to proteids has also been investi- 

 gated by permitting digestive enzymes to act on antitoxic serum. 

 Pick 2 digested the antitoxin-containing globulin of horse serum 

 for several days with trypsin ; after five days, when part of the 

 albumin was still not digested, the antitoxin was but little im- 

 paired in strength ; after nine days, when most of the proteid 

 was digested, the antitoxin had lost two- thirds of its strength. 

 This indicates a considerable resistance of antitoxin to trypsin, 

 but also shows that it is affected in much the same way as the 

 globulin (which is itself very resistant to trypsin) and therefore 

 is presumably of similar nature. Antitoxin seemed to be much 

 more rapidly destroyed by pepsin-HCl digestion than by tryp- 

 sin, in which respect it again resembles the serum globulin. 



In favor of the view that antitoxin is a definite proteid body 

 is also the fact that it is not carried down in indifferent precip- 

 itates, as are the enzymes, but comes down always in a certain 

 fraction of the proteid precipitates, e. g., we can precipitate all 

 the serum albumin from an antitoxic serum, and it does not 

 carry down with it any of the antitoxin. Another important 

 point has been brought out by Arrhenius and Madsen, 3 who 

 determined approximately the molecular weight of toxin and 

 antitoxin by means of their rate of diffusion, and found that 

 the toxin (diphtheria toxin and tetanolysin) diffused ten or more 

 times as rapidly as the corresponding antitoxin. This indicates 

 that the antitoxin molecules are much larger than the toxin 

 molecules, agreeing with the idea that antitoxin is of proteid 

 nature and that toxin is not. 



Taken all together, the evidence indicates a closer resemblance 

 of antitoxins to proteids than has been shown for the toxins, 



1 Medical News, 1904 (84), 375. 



2 LOG. tit. 



3 Festskrift Statens Serum Institut, 1902. 



