EQUILIBRIUM OF COLLOID AND CRYSTALLOID 301 



and the equilibrium between protoplasm and ion thus destroyed, 

 the cell activities are immediately affected, and after a short 

 period of pathological activity everything comes to rest. 



An analogy with another form of energy transformer may 

 make this clearer. If the fires are banked under the boiler of a 

 steam-engine the head of steam in the boiler will for a longer or 

 shorter period keep the steam-engine going: this is comparable to 

 stopping the organic food-supply of the cell; but if there is a 

 sudden burst in the boiler, if the cylinder blows off, or if there is 

 a break in any essential part of the machinery, then there is a 

 sudden stoppage of the engine, often preceded by a very brief 

 period of excessive activity : this is comparable to interference 

 with the inorganic ions of the cell. The inorganic ions form in fact 

 an intrinsic and indispensable part of the cell's structure, in the 

 absence of which it can no longer utilise its food-supply, however 

 abundant that supply may be or suitably adapted for the nutrition 

 of the normal cell. 



These effects, although they may be demonstrated in any living 

 tissue, are seen perhaps most typically in the case of the isolated 

 and perfused heart muscle. If the fluid caused to flow through 

 the heart consists of distilled water, to which organic foodstuff, 

 in the form, say, of dextrose, has been added, the heart-beat ceases 

 almost instantaneously. If next the experiment be repeated upon 

 a fresh heart, using instead a solution of pure sodium chloride 

 in distilled water, of such concentration that it is isosmotic with 

 the natural serum of the animal, there ensues a considerably longer 

 period of perhaps some minutes' duration before the heart-beat 

 disappears. The sodium chloride solution, however, although 

 possessing the proper osmotic pressure, is unable for any con- 

 siderable time to preserve the heart-muscle cells in normal con- 

 dition. By supplying the proper osmotic concentration it has 

 prevented the cells being suddenly broken up, but it has a zero 

 pressure for certain ions indispensable to the heart's activity; 

 these have slowly diffused out, and the period of the heart's action 

 has been determined by that moment at which the concentration 

 in the protoplasm has reached a certain minimal value. 



The most important of the ions which have been washed out 

 of the cardiac muscle cells by the current of pure sodium chloride 

 solution are the potassium and calcium ions. It still possesses 

 abundance of combustible organic material to furnish the energy 



