476 IMMUNITY. 



mixtures are allowed to stand before filtration the less 

 toxine passes, till a time is reached when no toxine is found 

 in the filtrate. Further, if the portion of fluid which at 

 this stage has not passed through the filter be injected into 

 an animal, no symptoms take place. This shows that after 

 a time neutralisation is complete. Other points of re- 

 semblance to simple chemical union are found in the facts 

 that neutralisation takes place more rapidly in strong solu- 

 tions than in weak, and that it is hastened by warmth and 

 delayed by cold. It has been found that if these factors 

 be taken into account and a standard toxine of definite 

 strength be employed, a toxine can be titrated against an 

 antitoxine with corresponding accuracy to what obtains in 

 the case of an acid and an alkali. These facts are strongly 

 in favour of toxine neutralisation consisting in a chemical 

 union, and such a view would also throw light on the other- 

 wise somewhat puzzling fact that while, e.g., by lapse of time 

 the toxicity of a toxine may become diminished, it may still 

 require the same proportion of antitoxine to neutralise it as 

 it did before. On the chemical theory this, according to 

 Ehrlich, is due to the disintegration of the toxophorous 

 atom group of the toxine molecule (vide p. 161), while the 

 combining (haptophorous) group still remains unaltered. 

 Quite analogous cases could be cited from pure chemistry. 

 The next question to be considered is the mode of pro- 

 duction of antitoxines. In the first place, we have evidence 

 of naturally existing antitoxines. Wassermann and Takaki 

 and others have shown, that in the grey matter of the central 

 nervous system of animals susceptible to tetanus there nor- 

 mally exist bodies which have the power of neutralising a 

 certain amount of tetanus toxine, presumably by combining 

 with it. This neutralising power is of course demonstrated 

 by injections in another animal. Similarly in some horses 

 the serum has been found to have antitoxic properties 

 against diphtheria toxine, and Fraser has shown that ox- 

 bile has a degree of antitoxic action against serpents' 

 venom. It may further be noted here that in the nervous 

 system of the common fowl, on which tetanus toxine has 



