266 ENERGY CHANGES INVOLVED IN SECRETION 



quantity Q grms. in solution at pressure p l to pressure p 2 will be 



RT 2 log P *. 



M & p l 



If now there are any number of substances A, B, C . . . N in 

 solution in the secretion in quantities Q a , Q,,, Q, ; . . . Q , and the 

 molecular weights of the substances be M,,, M/,, M c . . . M w , and 

 the pressures of the substances in the lymph be represented by 

 Pa> Pb> PC- - p n > an d the corresponding pressures in the secre- 

 tion by p' n9 p' h , p r . . . 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 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 : 



= og. 



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 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 concentrations of urea 

 in plasma and urine are respectively 0-04 and 2-0 per cent. 

 in the human organism, the similar concentrations of sodium 



