THE president's ADDRESS. 341 



also exhibit specific form. No lifeless things reproduce their 

 kind, but reproduction may be regarded as discontinuous growth, 

 and the offspring produced by a living body is not always 

 similar to the parent, but sometimes very different from it, as in 

 the well-known phenomena of alternation of generations. No 

 inanimate object, however, exhibits sexual characteristics or 

 psychical faculties. 



Analysis of the properties of living things shows that their 

 most distinctive characteristic is that which is known as 

 metabolism, signifying that, however distinctive and apparently 

 constant the form and characters of the living body may be, 

 considered as a whole, its substance is undergoing incessant 

 change. A living organism of any kind takes up substances 

 from its environment and causes them to undergo chemical 

 changes which result in their being built up into the substance 

 of the living body itself. At the same time the living substance 

 is also undergoing changes which result in its breaking down, 

 with production, on the one hand, of simpler and more stable 

 compounds than those which constitute the living substance, 

 and, on the other hand, of energy in various forms, such as 

 movement, heat, electrical changes, etc. Hence the principal 

 manifestation of life is the exercise of two processes of change 

 of substance ; the one, termed anabolism, is the building up of 

 the complex chemical substances composing the living body from 

 simpler materials ; the other, termed catabolism, is the breaking 

 down of these complex bodies in order to generate energy. If 

 the process of building up the body-substance is more active than 

 that of breaking it down, as is usually the case, the result is 

 growth or reproduction. The growth of a living body is there- 

 fore quite different from that of a not-living body, such as a 

 crystal, which grows without chemical assimilation. A crystal of 

 salt or sugar, for instance, can only grow in a liquid in which 

 salt or sugar has been dissolved ; but to grow a fern in a pot, it 

 is not necessary to supply it with solution of fern, but only with 

 water containing inorganic salts, air and light : then by means 

 of the energy absorbed from the sun's rays the fern is able to 

 absorb the simple substances that it obtains from its environment, 

 to build them up into the complex fabric of its body, and to grow. 



Whatever the form or specific characteristics of a living body, 

 this fundamental vital property of metabolism remains its most 



