CHEMICAL NATURE OF ANTITOXINS. 477 



accordingly simply state the facts ascertained. We may note, 

 however, that it is not a serious objection that in certain animals 

 other tissues than that of the central nervous system can combine 

 with tetanus toxin — this might take place with or without result- 

 ling symptoms ; the important fact is that in the nervous system 

 certain molecules have an affinity for the toxin. 



It will be seen from what has been stated with regard to the 

 relation of toxin and antitoxin, that the fixation of toxin by the 

 tissues leads up theoretically to the possible production of anti- 

 toxin. In other words, the substance which, when forming part 

 of the cells, fixes the toxin and thus serves as the means of 

 poisoning, may act as an antitoxin when free in the blood. This 

 will be discussed below in connection with Ehrlich's theory of 

 passive immunity. 



We may conclude this portion of the subject by saying that 

 (i) zV is practically proved that antitoxin acts as such by combining 

 •with toxin, and (2) dntitoxin, is probably represented by molecules 

 normally present in the cells or ignore rarely^ in the fluids of the 

 body. 



Within recent years a large number of anti-substances have 

 been obtained against substances other than toxins. As ex- 

 amples we may mention precipitins, which are produced by the 

 injection of the serum of another animal, and which produce 

 an opacity when added to that serum ; various anti-ferments, e.g. 

 anti-rennet, anti-coagulins, also anti-complements (vide p. 482). 

 All these act in a manner corresponding to antitoxins ; for 

 instance, the addition of anti-rennet to milk prevents the latter 

 being curdled by rennet. Their production is apparently 

 governed by the same laws. 



Of the chemical nature of antitoxins we know little. From 

 their experiments C. J. Martin and Cherry deduce that while 

 toxins are probably of the nature of albumoses, the antitoxins 

 probably have a molecule of greater size, and may be allied to 

 the globulins. Hiss and Atkinson have also come to the con- 

 clusion that antitoxin belongs to the globulins. They found that 

 the precipitate with magnesium sulphate from anti-diphtheria 

 serum contained practically all the antitoxin, and that any sub- 

 stance obtained which had an antitoxic value gave all the 

 reactions of a globulin. They also found that the percentage 

 amount of globulin precipitated from the serum of the horse 



