342 THE president's address. 



distinctive peculiarity, the mark and sign of life. The metabolic 

 process varies infinitely in detail in different cases, but remains 

 throughout the same in principle : a chemical transmutation of 

 substances to build up the complex material of the living body, 

 and the breaking down again of the living substance to produce 

 energy. The process of metabolism may be temporarily in 

 abeyance, but complete inhibition and permanent cessation of 

 metabolism means death ; the body ceases to be living and 

 becomes merely a mass of inert and lifeless substance. If a 

 living body appears to us as a stable body, the fact is due solely 

 to the limitations of our senses, which cannot take cognisance of 

 the process of incessant change that is going on. Could we either 

 magnify the substance of the living fabric, or increase the range 

 of perception of our senses to such an extent that we could 

 actually observe the chemical and physical changes taking place, 

 then a living organism, however minute, would appear to us to 

 hum like a factory or roar like a furnace. Chemical molecules 

 are being taken in, broken up, their constituent atoms combined 

 with others to build up huge molecules containing hundreds and 

 thousands of atoms in more or less unstable union. These mole- 

 cules in their turn are breaking down and smaller groups of 

 atoms are being set free with explosive suddenness, producing 

 heat, movement and other forms of energy. 



If now we examine further into the composition of living bodies, 

 we find them to contain universally a substance known as 

 protoplasm, which presents itself as a viscid, slimy fluid, very 

 rarely clear and transparent and then only in parts, but as a 

 rule turbid and containing great numbers of granules and 

 enclosures of various kinds. Some living bodies consist entirely 

 of protoplasm : in others various structures and mechanisms are 

 produced in and by the protoplasm, and by this means a very 

 complex organisation may be produced. The general statement 

 can be made, however, that living bodies consist either of 

 protoplasm alone or of protoplasm combined with the products 

 of its own vital activity. Protoplasm may, in short, be identified 

 as the material basis of life. 



When this substance, protoplasm, is examined further, it is 

 found that from the chemical point of view it consists chiefly of 

 substances known as proteins, the most complex chemical sub- 

 stances known. A famihar example of a protein is albumin. 



