10 LIFE: ITS NATUBE, OEIGIN AND MAINTENANCE 



among the characteristic phenomena of life are the processes of assi- 

 milation and disassimilation, the taking in of food and its elaboration.* 

 These, surely, it may be thought, are not shared by matter which is not 

 endowed with life. Unfortunately for this argument, similar processes 

 occur characteristically in situations which no one would think of 

 associating with the presence of life. A striking example of this is 

 afforded by the osmotic phenomena presented by solutions separated 

 from one another by semipermeable membranes or films, a condition 

 which is precisely that which is constantly found in living matter.! 



It is not so long ago that the chemistry of organic matter was 

 thought to be entirely different from that of inorganic substances. But 

 the line between inorganic and organic chemistry, 



which U P to the middle of the last century appeared 

 sharp, subsequently became misty and has now dis- 

 appeared. Similarly the chemistry of living organisms, which is now 

 a recognised branch of organic chemistry, but used to be considered as 

 so much outside the domain of the chemist that it could only be dealt 

 with by those whose special business it was to study * vital ' processes, 

 is passing more and more out of the hands of the biologist and into those 

 of the pure chemist. 



Somewhat more than half a century ago Thomas Graham published 

 his epoch-making observations relating to the properties of matter in 



the colloidal state : observations which are proving 

 Tli6 colloid coiistitu- n L ' j t *ii 



tion of living; matter all-important in assisting our comprehension of the 



identity of physical properties of living substance. For it is becoming 



c?s d ses Cl in*lfrin ^ad every day more a PP arent that the chemistry and 

 non-living matter. physics of the living organism are essentially the 

 chemistry and physics of nitrogenous colloids. Living 

 substance or protoplasm always, in fact, takes the form of a col- 

 loidal solution. In this solution the colloids are associated with crystal- 

 loids (electrolytes), which are either free in the solution or attached 

 to the molecules of the colloids. Surrounding and enclosing the 

 living substance thus constituted of both colloid and crystalloid material 

 is a film, probably also formed of colloid, but which may have a 

 lipoid substratum associated with it (Overton). This film serves the 

 purpose of an osmotic membrane, permitting of exchanges by diffusion 



* The terms ' assimilation ' and ' disassimilation ' express the physical and chemical 

 changes which occur within protoplasm as the result of the intake of nutrient material 

 from the circumambient medium and its ultimate transformation into waste products 

 which are passed out again into that medium ; the whole cycle of these changes being 

 embraced under the term ' metabolism. ' 



f Leduc (The Mechanism of Life, English translation by W. Deane Butcher, 1911) 

 has given many illustrations of this statement. In the Report of the meeting of 1867 

 in Dundee is a paper by Dr. J. D. Heaton (On Simulations of Vegetable Growths by 

 Mineral Substances) dealing with the same class of phenomena. See also J. Hall- 

 Edwards, Address to Birmingham and Midland Institute, Nov. , 1911. The conditions of 

 osmosis in cells have been especially studied by Hamburger (Osmotischer Druck und 

 lonenlehre, Wiesbaden, 1902-4). 



