ON THE ELECTRICAL CHARGE OF PROTEIN. 145 



a positive or a negative charge? We create in this way 

 repellent electrical forces between the smallest particles 

 of colloidal material, which will work against the surface 

 tension, which tends to make them coalesce and pre- 

 cipitate. If the protein is given an electrical charge 

 through the addition of a little acid or alkali, then, as 

 experiment shows, its precipitation through alcohol is 

 inhibited or entirely prevented. We may imagine from 

 this that for precipitation through non-electric forces 

 conditions must exist somewhat similar to those which 

 HARDY and BREDIG believed to exist for electrolytes. 



In passing it may be mentioned that our uncharged 

 protein is readily coagulable through heat and, as may 

 be imagined, through acetic acid-potassium ferrocyanide, 

 phosphotungstic acid, and phosphomolybdic acid. In 

 the first case we are dealing with an as yet not entirely 

 understood chemical change in the protein brought about 

 through the high temperature. In the second case the 

 protein is first charged positively through the acetic acid, 

 to be precipitated later by the various oppositely charged, 

 probably colloidal, acid ions. 



These conversion and precipitation experiments are 

 able to answer the question, In what electrical condition 

 do the proteins exist in the blood and the tissue fluids? 

 Since alkalies impart a negative, acids a strongly positive, 

 reaction to proteins, one is able to draw conclusions from 

 the reactions of animal fluids as to the charge of the 

 proteins contained in them. Modern investigations have 

 solved for us the question of the reaction of the tissue 

 fluids, or, to put it more accurately, the relation between 

 their content of H and OH ions. According to these 

 investigations, the body fluids are neutral. The free 



