11$ PHYSICAL CHEMISTRY IN MEDICINE. 



of aggregates in the process of colloidal precipitation, this 

 result was to be expected, for each of the toxin doses 

 added to L distributes itself over all the aggregates already 

 present, in consequence of which the mixture can attain 

 the unit toxicity only after several doses have been added 

 to it. 



Through an investigation carried out by the chemist 

 BILTZ, who has brought much light into this field, we 

 are familiar with phenomena observed upon inorganic 

 colloids that are entirely analogous to the EHRLICH 

 phenomena just described. BILTZ studied quantitatively 

 the neutralization of arsenious acid by its well-known 

 antidote, iron hydroxide, of which the former represents 

 an electronegative radicle, the latter an electropositive 

 colloid. These investigations showed that a neutralized 

 mixture of the two that is, one corresponding with the L 

 toxin-antitoxin mixture, therefore still has the power of 

 uniting with arsenious acid and rendering several poison- 

 ous single doses harmless. A certain analogue of the 

 EHRLICH phenomenon in the field of precipitation is per- 

 haps to be found in the following. It is often possible, as 

 has already been pointed out, to dissolve a precipitated 

 colloid in an excess of the precipitating colloid. If the 

 addition of a colloidal solution to a neutralized precipitated 

 mixture corresponding with the LO value of EHRLICH is 

 continued until the precipitate is redissolved, much more 

 of this colloid is required for this purpose than when a 

 colloid has added to it all at once an excess of a second 

 colloid. The intimate connection between this phenom- 

 enon and the behavior of a colloid when precipitated 

 through the addition of successive small doses of a second 

 colloid can readily be seen. The procedure is the same, 



