2 THE EQUILIBRIUM OF COLLOID AND 



inorganic ions, than it is by interfering with the supply of organic 

 foodstuffs. For, in the latter case, the cell can oxidise the com- 

 bustible materials present in storage within it, and even use up a 

 portion of its own intrinsic substance before its activities come to 

 a standstill ; but when the inorganic ions, forming a constitutional 

 part of the living cell, are altered, and the equilibrium between 

 protoplasm and ion thus destroyed, the cell activities are imme- 

 diately 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 



