ENERGY CHANGES INVOLVED IN SECRETION 161 



and the pressures of the substances in the lymph be represented 

 by p a , p b , p c ...... p n , and the corresponding pressures in the 



secretion by p' a , p' b , p' c ...... p' n \ then the expression for the 



work done upon each substance in its production from the pressure 

 in the lymph to the pressure in the plasma will be the same as 

 that given above for a single substance ; for example, for substance 



Q v' 



A the expression will be - RT log . Accordingly the -value 



of the total amount of work done against osmotic pressure (W) 

 will be given by : 





If any of the constituents is electrolytically dissociated, then 

 Q in the expression for the work done in separating it must be 

 multiplied by the dissociation factor, because the osmotic pressure 

 will be higher on account of the dissociation, and correspondingly 

 more work will be done in the separation ; thus in the case of the 

 sodium chloride of the urine, for example, at the concentration 

 at which that salt is there separated, it is almost completely dis- 

 sociated, and Q must be multiplied by the factor I 1 9 approximately 

 in order to obtain the amount of work done. 



The above investigation of an expression for the amount of 

 work done against osmotic energy in separating a secretion is 

 entirely different from that usually given, which is quite erroneous 

 in that it supposes all the constituents of the secretion to be 

 equally concentrated in the process of separation from the plasma. 

 Such a supposition is wrong in fact, and leads to quite a wrong 

 expression for the total amount of work done, as well as for the 

 work done upon each constituent. For example, while the con- 

 centrations of urea in plasma and urine are respectively 0-04 and 

 2-0 per cent, respectively in human urine, the similar concentra- 

 tions of sodium chloride are O55 and T10 per cent. ; and hence 

 in the expressions for the work done in secreting urea and sodium 



7) 



chloride respectively the factor log e has quite a different value 



in the two cases, being Iog e 50 in the case of the urea and Iog e 2 in 



L 



