2 9 2 SCIENCE PROGRESS. 



and has its osmotic pressure raised by the waste products 

 of the cellular metabolism. 



These few examples will serve to show the many 

 possible applications of the theory of osmotic pressures in 

 determining the work done in the chemical functions of 

 the body. It seems to me probable, however, that the 

 theory may be of yet wider application. In the paper 

 above quoted Heidenhain, after comparing the living cell 

 to a steamer which may, and often does, float down with 

 the stream, but can, under circumstances, move up against 

 the stream, points out that our knowledge of the structure 

 of this mechanism is so imperfect and restricted by instru- 

 mental shortcoming's that physiologists cannot at present 

 attempt to say how a given force is evolved in the cell, but 

 must confine themselves to locating the exact seat of the 

 energies in the body. I think this is perhaps rather too 

 pessimistic a view to take of our possibilities. Secretion- 

 pressure, movement, are among the phenomena regarded 

 as essentially vital, and yet the botanist will explain root- 

 pressure, movement, as consequences of changing osmotic 

 pressures. We know already that every manifestation of 

 activity is associated with katabolic changes, that is, a 

 breaking down of large unstable molecules into smaller 

 and more stable molecules, so that, wherever these changes 

 are going on, there must be a rise of osmotic pressure. All 

 we want is a suitable mechanism to direct the process, and 

 it is possible that we may explain muscular work, secretion- 

 pressure as directly due to these changes in osmotic 

 pressure. 



The possibility of such an explanation seems to have 

 struck several observers, but, so far as I am aware, no serious 

 attempt has yet been made to place an explanation along 

 these lines on a firm experimental basis. 



Ernest Starling. 



