ENERGY CHANGES INVOLVED IN SECRETION 165 



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 semi-permeable 

 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 semi-permeable membrane, 

 could form the secretion 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 semi-permeable 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 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 

 the dissolved molecules themselves, they may be caused to move 

 in a definite direction and at a definite speed through the cell, 

 different from that of the water in which they are dissolved. A 

 similar directive movement, in fact, to that seen in the case of 

 dissolved ions and colloidal molecules in the electric field may occur. 



