80 INTIMATE ASSOCIATIONS OF INORGANIC IONS 



potassium, etc. depends on its ionic pressure in the lymph as 

 well as on the affinity for it possessed by the particular tissue 

 in question. Certain forms of malnutrition may depend not 

 so much on the malabsorption of an inorganic ion as on the 

 diminished affinity for that substance as the result of some 

 intoxication or devitalisation of the living tissues. 



But even when an ion is present in the lymph in a concentra- 

 tion greatly above its concentration in the cell, that substance is 

 not absorbed in anything like the degree which one would expect 

 of it, if one had regard only to its concentration over iso-tonicity. 

 The living tissues have a "power of refusal." 



This explains what is so well recognized, that it is impossible 

 to over saturate the tissues with any of the mineral substances 

 iron, arsenic, calcium, or even oxygen. This fixedness of limit 

 for saturation of protoplasm by chemical substances explains 

 the impossibility of indefinite increase in bulk of tissues by 

 overfeeding with nitrogenous food, of increasing the intensity 

 of tissue-changes to any notable extent by the breathing of pure 

 oxygen by healthy persons or of increasing, for instance, the 

 iron or phosphorus content of the healthy red marrow or brain. 

 After being satisfied, the tissues have a power of refusal one 

 of the expressions of "functional inertia." 1 



The same line of reasoning applies to the gases concerned 

 in metabolism. Thus oxygen must be under a certain pressure 

 in order to enter properly into union with the living matter. 

 Whereas oxygen at the partial pressure of one-fifth of an atmos- 

 phere suffices for the perfusion fluid for a frog-heart, it must 

 be under the pressure of one atmosphere in the fluid 2 necessary 

 for the mammalian heart. In the actual blood, which could 

 not take up anything like this quantity of oxygen in solution, 

 this high pressure is functionally represented by the loose 



1. Harris, D. Fraser : The functional inertia of living matter. London, Churchill 

 1908. 



2. Ringer-Locke solution consists of 



NaCl, 0.9% NaH CO 3 0.01 to 0.0 37, 

 Ca Cb, 0.024% Dextrose, 0.1% 

 K Cl, 0.042% 

 Solution fed to the heart under the pressure of one atmosphere of oxygen. 



