CHEMICAL XATURE OF aMITOXIXS 181 



more an absoi'ption curve than the reaction curves of crystalloids, and 

 being influenced by all conditions that influence colloids. "Whether 

 the receptor groups are secreted in a free condition in antitoxin for- 

 mation, or combined in a large molecule, is unknown. 



By saturating serum with magnesium sulphate, or half saturation 

 with ammonium sulphate, three chief groups of proteins can be pre- 

 cipitatctl and isolated.^" These are fibrinogen, euglobulin (true 

 globulin), and pseudo-globulin (soluble in water). Pick^'' found that 

 the precipitate obtained by 36 per cent, volume saturation with am- 

 monium sulphate contained no antitoxin ; the antitoxin came down 

 in the precipitate obtained on raising the strength from above 38 

 per cent, to 46 per cent.'^^ According to Pick, in horse serum the anti- 

 toxin is associated with the pseudo-globulin, and Gibson and Banzhaf 

 found that the blood of hoi^ses immunized to either diphtheria or 

 tetanus toxin shows a marked increase (40 to 114 per cent.) in serum 

 globulin, varying somewhat according to the antitoxin content, the 

 more soluble globulins being most increased. At the same time the 

 serum albumin and euglobulin content decreases in proportion, while 

 the fibrinogen shows no characteristic alterations.^- Hurwitz and 

 Mej^er^^^ however, find in their study of the blood proteins during im- 

 munization, that the proportion of globulins increases according to the 

 severity of the intoxication, and not in any definite relation to the 

 degree of immunity. The average antitoxic horse serum contains 12 

 per cent, albumin, 78 per cent, of soluble globulin containing anti- 

 toxin, 10 per cent, euglobulin.^ By heating 12 hours at 57° a consid- 

 erable part of the soluble globulin becomes insoluble, without a corre- 

 sponding loss of antitoxin (Banzhaf). 



The relation of antitoxins to proteins has also been investigated 

 by permitting digestive enzymes to act on antitoxic serum. Pick di- 

 gested the antitoxin-containing globulin of horse serum for several 

 days with trypsin ; after five days, when part of the protein was 

 still not digested, the antitoxin was but little impaired in strength; 

 after nine days, when most of the protein was digested, the antitoxin 

 had lost two-thirds of its strength. This indicates a considerable re- 

 sistance of antitoxin to tryi3sin, but also shows that it is affected in 

 much the same way as the globulin (which is itself very resistant 



toxin and antitoxin move towards the cathode, which is opposed to the theory 

 tliat tliis reaction is simplv one of oppositely charged colloids. (See also Bech- 

 hold, Miinch. med. Woch., 1907 (54), 1921.)" 



49 See resume bv Gibson, Jour. Biol. Chem., 1905 (1). IGl : GibsoTi and Ban/.liaf, 

 Jour. Exper. Med., 1910 (12), 411. 



50 Hofmeister's Beitr., 1901 (1), 351. 



51 C4ibson and Collins (Jour. Biol. Chem., 1907 (3), 233) question the reliabil- 

 ity of some of Pick's results, and repudiate the salt fractionation metiiod of clas- 

 sifying proteins. 



52 During immuniyation the antitryptic power of tlie horse serum increases 

 with the antitoxin increase (Krause and Klug, Berl. kiln. \\(Hh.. 1908 (45), 

 1454. 



53 Jour. Exp. Med., 1916 (24), 515: 1917 (25), 231. 



