INTRINSIC ACTIVITY OF SECRETING CELLS 263 



each in equilibrium with B, and hence are in equilibrium with one 

 another, so that when the final concentrations are attained the ratio 

 of concentrations in A and C must be the same as if B were left out 

 and A and C had been placed in contact and allowed to come into equili- 

 brium. The only factor which affects the result apart from equilibrium 

 is the rate of diffusion of the substance x through the layer B, and this 

 may not bear any constant relationship to the solubility of x in B. 



We see, therefore, that a high solubility of any dissolved sub- 

 stance in a supposed lipoid membrane or in the cell protoplasm, 

 will cause a corresponding accumulation of that substance in 

 the lipoid membrane or in the cell protoplasm, but cannot act 

 as an engine or energy producer for sending the substance through 

 the cell as a secretion or an absorbed product. 



The substance taken up as a result of higher solubility, such 

 as an anaesthetic absorbed in lipoids, or by fat in ordinary adipose 

 tissue, is hence imprisoned to that same extent in the fat or lipoid, 

 and kept from attacking or combining with the protoplasm; and 

 accordingly the presence of such bodies, instead of aiding or causing 

 anaesthesia, acts in the opposite sense by forming a reservoir for 

 the anaesthetic where it is inert so far as the cell protoplasm is 

 concerned, which is its real objective so far as production of anaes- 

 thesia is concerned. 



The view expressed above, that those substances which are 

 actively absorbed and retained by the tissue cells form unstable 

 physical or chemical compounds with the cell protoplasm dependent 

 upon the osmotic pressure of such substances, cannot any more than 

 the others which have just been criticised be put forward as an 

 explanation of the active work of the cell in secretion and absorp- 

 tion, when the product is not to be retained in the cell, but is to be 

 turned out in greater concentration than that at which it entered. 

 For substances in such unstable combination, although subject to 

 different laws of relationship between concentration and osmotic 

 pressure, obviously come into equilibrium also at a given point 

 of concentration and osmotic pressure, and hence their formation 

 cannot be turned into a continuous source of energy for the per- 

 formance of work by the cell, such as is required to fit the case of 

 secretion. 



The formation of such unstable compounds is capable of ex- 

 plaining the selective uptake and retention of constituents by the 

 cell, just as the different solubilities of different constituents by the 



