146 PHYSICAL CHEMISTRY IN MEDICINE. 



hydrogen and hydroxyl ions exist in them in the same 

 proportion as in water. This is shown most harmoni- 

 ously not only through tests with proper indicators, 

 such as phenolphthalein, but also through electrical 

 measurements. Litmus, which was formerly employed 

 as an indicator, is itself too strong an acid to show 

 the presence of the weak acids of the tissue fluids, 

 and indicates therefore an alkaline color reaction. If 

 we remember that uncharged protein cannot be pre- 

 cipitated through the positively charged heavy metals, 

 while the proteins of the tissue fluids can at once be 

 precipitated by them, the conclusion is inevitable that 

 native protein carries a negative charge. This charge 

 can be derived only from the hydroxyl ions that are split 

 off from the salts of the serum, which, in harmony with 

 the above-described experiments, must be the carbonates 

 and phosphates. If sodium bicarbonate is added to fresh 

 non-charged protein, this assumes a strong negative 

 charge even though the resulting mixture is neutral 

 toward litmus and acid toward phenolphthalein. In an 

 experiment conducted with such a sodium bicarbonate- 

 protein, it was found that the relation of nitrogen at the 

 cathode was to that at the anode as 3:5; while the 

 nitrogen content of the middle beaker was expressed by 4. 



IV. 



We are now acquainted with sufficient facts to study 

 more closely the conditions for the precipitation of 

 native electronegative protein, and to compare these 

 whenever necessary with those of uncharged or artificially 

 charged protein. 



