6 THE EQUILIBRIUM OF COLLOID AND 



The most essential and as it were the central constituents in 

 building up the excessively complex physico-chemical aggregation 

 which we term protoplasm or bioplasm, are the protein bodies. 

 By means of the proteins, the fats and carbohydrates are knitted 

 together with the variously constituted proteins themselves and 

 with the ions of the inorganic salts to form a united system. The 

 component parts of this system are only lightly held together, 

 each is held in by the pressure of a free portion of it in the cell 

 fluid, and for the life and activity of the cell it is essential that 

 the osmotic pressure of each constituent should lie within a certain 

 range, so that it neither becomes fixed quite permanently nor so 

 completely liberated as to be absent from the cell when it is required 

 for the chemical transformations which yield the supply of energy 

 to the cell. During the molecular vibrations which accompany 

 this labile equilibrium in which the intensities of attachment of the 

 various constituents to the bioplasm are all the time varying, the 

 organic oxidisable substances, viz. the proteins themselves, the 

 fats and carbohydrates, suffer temporary molecular disruptions 

 during which the oxygen also held in the bioplasm comes into 

 union with them, and the oxidised products as they increase in 

 pressure are shed off from the cell. 



As has been stated above, the inorganic ions exercise the 

 function in the cell of favouring these chemical disruptions, for 

 when by lowering their osmotic pressure in the cell fluid they are 

 dissociated off from the bioplasm, the oxidation processes which 

 form the chemical basis for the cell's activities also come to 

 an end. 



Although it is impossible at the present time to^aj^iJSfiiail^ 

 synthesise any of the proteins of the cells or body fluids, and still 

 less to build these up synthetically with the other constituents 

 mentioned above into bioplasm, or living matter, yet we have even 

 now obtained much insight as to the general character of the con- 

 stitution of proteins, and the main plan upon which details are 

 still to be worked out lies before us. 



This knowledge has been arrived at by two different channels 

 of approach, viz. that of studying the cleavage products of proteins 

 in which Schiitzenberg was the great pioneer, followed by a host 

 of others ; and that of building together such cleavage products 

 into bodies closely resembling in many respects- the naturally 

 occurring proteins, in which Emil Fischer is now leading the way, 



