IONS IN IMMUNITY 121 



which for the complement is carried to the maximum. 

 The amboceptor exercises the function of bringing 

 about a modification of the conditions which deter- 

 mine the distribution of the complement. It causes 

 the complements to become monotropic by union 

 with its substance ; and the complements are 

 localised by amboceptors which are united with 

 some other substance such as the cells. Such is 

 the amboceptor theory of Ehrlich. 



That the proteid substances are able to act upon 

 one another is undoubted. But all authorities are 

 not agreed upon the foregoing explanation. Ehrlich's 

 theories are not accepted without an attempt being 

 made to render the subject somewhat clearer. This 

 attempt is made through the study of the action of 

 ions upon colloids and by the laws of colloidal 

 chemistry ; to which we must now return, 



" Let us suppose that a sufficient number of ions 

 are introduced into a colloidal solution of a metal, 

 which represents a suspension of weakly charged 

 electro-negative particles. In consequence of elec- 

 trical attraction, the negative colloidal particles will 

 collect about the electro-positive ions, until, through 

 the heaping up of a sufficient number of such par- 

 ticles, the collecting ions will be electrically neutral- 

 ised. When the aggregates thus formed have 

 reached a sufficient size, the solution becomes turbid 

 and finally a precipitate drops to the bottom."* 

 According to the ionic theory a similar process takes 

 place in the reactions of precipitins, agglutinins, and 

 probably the antitoxins. 



* Pauli's "Physical Chemistry in the Service of Medicine," 

 p. 109, 



