214 PRINCIPLES OF GENERAL PHYSIOLOGY 



neutralised by any amount of either calcium or sodium salt nor by both 

 together. 



The fact that calcium has a much more powerful action than sodium has is not 

 unexpected if we look upon the effect as exerted on the cell membrane. Ca* ', as 

 a bivalent ion, has much greater action on colloidal aggregation than sodium has. 

 Strontium chloride has an effect about equal to that of calcium chloride ; barium 

 chloride has also a high value, but is very toxic. Magnesium chloride has 

 relatively little action, so that the valency of the ion is not the only factor 

 concerned. 



Sodium chloride, in the concentration in which it exists in sea water, cannot 

 be neutralised by potassium chloride alone, calcium must also be present. 



A further interesting fact is that the toxic action of acids is also abolished by 

 sodium ions and still better by calcium ions. 



If electrical phenomena play a part in the action of ions in general, it is possible that 

 the affinity of an ion for its charge may have to be taken into account, as insisted upon by 

 A. P. Matthews (1904). The most active ions would be expected to be those which part 

 with their charges most easily. Although we must admit, with this author, that physiological 

 action has frequently no connection with chemical structure, for example, beryllium sulphate, 

 lead acetate, sugar, phloroglucinol and saccharin all taste sweet, it is undoubtedly going 

 too far to say that all actions of enzymes or toxins have nothing to do with chemical structure, 

 or that the action of a lead or other salt on the living organism is determined by tin- 

 character and number of its electrical charges and by the ease with which it parts with 

 these charges, and by nothing else. 



ACTION OF SALTS IN PARTICULAR INSTANCES 



In order to realise the many and various ways in which electrolytes intervene 

 in physiological processes, it will be instructive to refer briefly to a few typical 

 cases ; some of these will require more detailed treatment in future chapters, so 

 that they may be merely mentioned here. 



The illustration by Hoeber (1911, p. 444) of our methods of regarding the 

 combined effect of the various ways in which such actions may be exercised, is an 

 apt one. He likens our conceptions to a mirror, which, in its present condition, 

 does not give a sharp image. If the image appears to be a confused one, we must 

 not jump to the conclusion that the mirror itself is an inappropriate one and 

 distorts the object to be reflected, but that it is not sufficiently polished to show 

 fine details as well as it does the coarser outlines. The physical chemistry of 

 colloids, to mention one fact only, is still too full of gaps to answer all that it 

 may be capable of. 



It is perhaps well to name again the possible ways in which a salt or other 

 electrolyte may act ; the electrical charge, as such, has its effect ; there is also the 

 effect on the solvent, shown by lyotropic actions, and frequently expressed in the 

 " Hofmeister series " ; finally, we may have effects, not included in any of these 

 and more nearly related to purely chemical action, so that they are often exerted 

 by the salts of one element alone, or by those of closely related ones. 



The Sitjn of the Electrical Charge on Cell Membranes, as worked out by Mines 

 (1912), is the first of these general effects to which we may call attention. 



On Adsorption by Surfaces. When a substance with an electrical charge is 

 adsorbed by the surface of a colloid, the amount adsorbed depends greatly on 

 the sign of the charge of the surface, whether similar or opposite to that of the 

 substance adsorbed. By electrolytes, the charge of the surface can be annulled 

 or reversed. 



Hamoglobin. An important action of electrolytes on the dissociation of 

 oxyhaemoglobin, described by Barcroft and Camis (1909), probably depends on the 

 colloidal nature of this substance. At a given pressure of oxygen, less of this 

 gas is taken up by haemoglobin in presence of salts than in pure water. For 

 example, at 30 mm. of mercury of oxygen pressure, the percentage saturation 

 in water is 85, and in Ringer's solution only 60. The effect is still more marked 

 with acids, and is a delicate indication of the hydrogen ion concentration in 

 blood. The importance of these facts will be seen later in connection with the 

 supply of oxygen to the tissues. 



