CHANGES WROUGHT /A/ PATHOLOGY. H7 



chemical compositions. We are able to recognize in this 

 only a general property of colloidal mixtures, the laws 

 governing which ZSIGMONDY has formulated in his inves- 

 tigations on CASSIUS'S gold-purple in the following way: 



" As most important I consider the recognition of the 

 fact that a mixture of colloids may, under certain circum- 

 stances, behave as a chemical compound, and that the 

 properties of one of the constituents of such a mixture 

 may be concealed through those of another." 



An especially remarkable illustration of the identity 

 of the neutralization of toxin with antitoxin and the 

 neutralization of two colloids is furnished by a phenomenon 

 which has also been discovered by EHRLICH, and a de- 

 scription of which we will introduce, with a few figures. 



As the standard of a lethal dose of diphtheria toxin 

 is taken the amount which will kill a guinea-pig of 250 

 grams in from four to five days. EHRLICH added to one 

 immunity unit that is, one cubic centimeter of antitoxin 

 serum, capable of counteracting the poisonous effects of 

 100 simple lethal doses enough diphtheria toxin until 

 the mixture showed no toxic properties and indicated 

 the amount of toxin necessary to accomplish this by 

 L . This is usually less than one hundred, for the neu- 

 tralizing toxin has, as a rule, stronger neutralizing than 

 toxic properties. Without a knowledge of the properties 

 of colloids one would expect that through the addition of 

 a simple toxic dose to the approximately neutralized mix- 

 ture L one would obtain a product capable of killing 

 a normal guinea-pig in from four to five days. EHRLICH 

 found', however, that several simple toxic doses have to 

 be added before the mixture again assumes the effect of 

 a free lethal dose. From our knowledge of the formation 



