250 INTRINSIC ACTIVITY OF SECRETING CELLS 



as the saliva where the total osmotic pressure is less than that of 

 the plasma, the osmotic pressure of certain constituents is higher 

 than their pressure in the plasma for example, in the saliva, the 

 pressure of dissolved carbon dioxide, of calcium salts, and of the 

 sulphocyanide ; (3) that new constituents appear in the secretion 

 as a result of chemical activity in the cell which are entirely absent 

 in the plasma, and are not sent into the plasma, but into the gland 

 duct, by means of cellular activity and in opposition to the operation 

 of osmotic energy; (4) the alteration in many cases of chemical 

 reaction by concentration of hydrogen or of hydroxyl ions in the 

 secretion high above the concentration which they possess in the 

 plasma, may be quoted as an example of cellular activity producing 

 an effect in opposition to osmotic pressure. 



Now it is clear that while the source of energy residing in the 

 blood-pressure might separate a secretion, with concentration 

 possessing any value up to that of the same dissolved constituent 

 in the plasma, it cannot produce a concentration in even a single 

 constituent exceeding the value of the concentration of that same 

 constituent in the plasma, and certainly cannot produce a new 

 constituent not present in the plasma. When the results of ex- 

 periment are taken in conjunction with this statement, it is found 

 that in every secretion in the body cellular activity must be brought 

 into action in other words, the secreting cell must furnish energy 

 in the process of secretion and this not only holds obviously for the 

 new constituents, but also for all those crystallised and inorganic 

 constituents which are found in the secretion at a higher concentra- 

 tion than in the plasma, and hence possess more osmotic energy. 



Not only does the increase in concentration of certain con- 

 stituents in the secretion above their concentration in the plasma 

 rule out, as far as these constituents are concerned, the operation 

 of nitration and osmosis, but it also rules out any passive view of 

 the secretion whatever which does not involve work done by the 

 cell as an active energy transformer. 



// any single substance is increased in concentration in a secretion 

 above the concentration which it possesses in the plasma, then such 

 increase in concentration involves the performance of work against 

 osmotic pressure, 1 and in consequence the expenditure of energy by 



1 This does not mean that the osmotic pressure is balanced or overcome 

 by hydrostatic pressure in the cell, but that osmotic or volume energy must 

 be replaced by energy in another form by the agency of the cell. 



