270 ENERGY CHANGES INVOLVED IN SECRETION 



transformation of a corresponding small amount of the energy 

 which it takes up as nutrient matter from the plasma. That 

 anything approximating to the osmotic pressure of the separated 

 urine develops in this process of energy transformation, or indeed 

 that there is any pressure developed whatever, we possess not 

 the smallest fraction of experimental evidence. All that is known 

 is that there is a small increase in osmotic energy, provided by 

 the expenditure of energy by the secreting kidney cell. The view 

 that the kidney cell is something in the nature of a semipermeable 

 membrane with a difference in pressure upon its two ends of many 

 atmospheres of pressure is an entirely erroneous one; no cell in the 

 body could withstand such a difference in pressure for a moment; 

 there is no evidence that such a pressure exists in the kidney tubules 

 in fact, it most certainly does not exist. Finally, no arrangement 

 in the nature of a semipermeable membrane could form the secre- 

 tion with accompanying concentration of dissolved substances. 

 In the first instance, because for such an operation, as has already 

 been pointed out, energy is required which a semipermeable 

 membrane cannot yield. Since an energy machine such as the cell 

 must be utilised for producing the secretion, we at once lose on the 

 introduction of such a machine all necessity for the maintenance of 

 hydrostatic pressure in opposition to osmotic pressure, and there is 

 no more reason why the kidney cells should be supposed to be exposed 

 to the osmotic pressure than there is to suppose that the walls of the 

 bladder should have to withstand the osmotic pressure of the urine 

 after it has been secreted and passed into the bladder. 



In an exactly similar manner, the work done in the secretion 

 of any constituent of any secretion can be calculated if the pressures 

 or concentrations in plasma and secretion and the amount of 

 secreted substance and volume of secretion are known. 



As to the mechanism or type of energy transformation by 

 which the cell does its work nothing is known ; similar phenomena 

 of concentration of ions and of dissolved colloids by means of 

 movement in the electric field have long been known, and it is 

 probable that it may be the case that the living secreting cell, 

 by developing differences in electrical potential at its two ends, 

 or by developing differences in energy potential of some other 

 form of energy such as that which intrinsically belongs to the 

 living cell, may establish a directive influence upon substances 

 in solution, as a result of which, and of energy potentials upon 



