VARIABILITY OF THAT CHARGE 95 



portant is a proper balance of the salts in the 

 organism. Hober has found by experiment that the 

 red blood corpuscles, under normal conditions, are 

 negatively charged ; but that they are susceptible 

 to changes which depend upon variations in the en- 

 vironment, especially changes in the ionic constitu- 

 tion and concentration. For example, in an iso- 

 tonic sugar-sodium-chloride mixture the red blood 

 corpuscles become electro-positive under the influ- 

 ence of C0 2 , and regain their normal reaction when 

 the CO o is withdrawn.* The inference is that red 

 blood corpuscles suffer a complete change in their 

 electrical reaction during their passage through the 

 pulmonary circulation. Many other cells likewise 

 show this variability in electrical reaction. Accord- 

 ing to modern investigations the fluids of the body 

 are neutral ; the free H and OH ions exist in them in 

 the same proportion as in the molecule of water. 

 How then is the variability in the reaction of cells 

 to be explained ? Why for instance do the red 

 blood cells change their reaction when their environ- 

 ment is changed ? or why does a protein assume a 

 positive electrical charge when it is exposed to the 

 presence of an equal number of H and Cl ions ? It 

 is because the colloid is semi-permeable to ions ; the 

 protein takes up more H than Cl ions ; and the same 

 liolds good for OH ions when it is submitted to the 

 influence of alkalies. The red blood corpuscle 

 becomes positive when exposed to the presence of 

 CO 2 because it is permeable for some of the negative 

 ions which it contains and which leave it, whereby 

 an excess of the positive ions remains. 



* Loc. cit., p. 150. 



