120 PHYSICAL CHEMISTRY IN MEDICINE. 



from each other. If we begin with an excess of toxin 

 to which successive small amounts of antitoxin are added, 

 the formation of aggregates will be able to follow a 

 different course than when the reverse is the case, when 

 we start with an excess of antitoxin. EHRLICH has 

 worked according to the first method, while PICK and 

 SCHWONER utilized the second method and came to the 

 conclusion that the laws governing the combination 

 between toxin and antitoxin were totally different from 

 those discovered by EHRLICH.* It can easily be seen 

 how through changes in only a few conditions an enormous 

 variety in the character of the colloidal reactions is 

 brought about, a behavior which is rendered apparent 

 through a consideration of the numerous well-studied 

 transitions existing between colloids and crystalloids. 

 A colloidal solution consists of a suspension of fine par- 

 ticles which have assumed an electrical charge through 

 giving off ions, just as have electrodes. If now the 

 suspended particles become steadily smaller, while at the 

 same time their electrical charge grows, they approximate 

 more and more the behavior of ions, until finally the 

 colloid passes over into a crystalloid, which dissociates 



* The relations existing here can be illustrated also by examples of 

 protein precipitation. The precipitation of protein through the heavy 

 metals is dependent upon the neutralization of the negative protein 

 through the positive colloidal metallic hydroxide. The precipitates 

 formed are, however, not soluble to the same extent in excesses of the 

 individual colloids. The silver-protein precipitate is, for example, soluble 

 in an excess of protein, but not in an excess of the silver salt. In th e 

 former case we have to do with the formation of variable aggregates' 

 in the second with simple neutralization according to the manner 

 observed by Pick on his toxostabile sera when large amounts of anti- 

 toxin have toxin added to them. 



