322 THE EQUILIBRIUM OF COLLOID AND 



dialysis or incineration and titrated to the same indicator, the 

 alkalinity now amounts to only 0-03 to 0-04 normal. Subtracting 

 these amounts due to inorganic constituents from the higher figure. 

 we obtain the result that the combining power of the serum pro- 

 teins alone for acid is equivalent to about 0-14 normal. 1 Now 

 the interesting point about this figure is that it coincides almost 

 exactly with the total osmotic concentration of all the salts naturally 

 occurring in the serum or plasma. The depression of freezing- 

 point of mammalian sera is on the average equivalent to that of a 

 0-9 per cent, solution of sodium chloride, and the molecular weight 

 of sodium chloride being 58, this corresponds to a 0-15 normal 

 solution. 



In addition to this direct evidence from the chemical side, 

 there are certain physiological correspondences between amounts 

 of protein and crystalloid in the blood which must be obeyed, or 

 otherwise the excess of salt in the plasma is removed by the kidneys. 

 This action comes into operation as soon as the plasma salts exceed 

 the amounts which can be loosely held by the proteins. 



The salts in cells are held more firmly adsorbed or combined 

 than is the case in the plasma, as is shown by effects on the elec- 

 trical conductivity and by the difficulty of dialysing the salts 

 from the cells. 



Thus it is found that although the osmotic concentration of 

 the salts in the red blood-corpuscles is nearly the same as in the 

 plasma, as shown by the depressions of freezing-points, 2 yet the 

 electrical conductivity of the separated corpuscles is only one- 

 fourteenth to one-seventeenth of that of the separated serum. 

 Part of this difference is mechanical and due to the envelopes of 

 the corpuscles rendering the conducting fluid non-homogeneous; 

 but even after removing this factor by laking, the conductivity of 

 the laked corpuscles still remains only at one-fifth to one-sixth of 

 that of the serum. This difference is undoubtedly due to the 

 attachment of the ions to the haemoglobin interfering with the 

 ionic velocities, for on dialysing against distilled water and then 

 reducing the volume of the dialysate to such a degree as to re- 

 present the original concentration of the salts before dialysis, it is 

 found that the conductivity of the free salts in the dialysate has 



1 The amount of this combining power of the protein may be better 

 appreciated by some if it be stated as equivalent to about 0-51 per cent, of 

 hydrochloric acid. 2 Vide infra. 



