A. E. HILTON ON THE NATURE OF LIVING ORGANISMS. 47 



freely, is restrained from acting violently; so that, once more, we 

 have the equilibrium necessary to life. 



We must now consider some of the products of the " automatic 

 chemical machinery" which has been described. Plasm is by no 

 means a perpetual motion machine, independent of surroundings. 

 On the contrary, unless reinforced from without, it speedily 

 exhausts itself, and either dies or its animation is suspended. 

 It works effectively only so long as it acts as a medium for the 

 intake and output of materials which it absorbs and modifies ; 

 and it thrives only so far as those materials are suitable for 

 conversion into addition plasm, or plasm-structures — in other 

 words, for the growth and upbuilding of the organism. 



One result of this constant " metabolism," or chemical chancre 

 of plasm and its working stock, is the production of acids. Now 

 life phenomena only occur in neutral media. Sea water, for 

 example, is practically a neutral fluid ; and the liquids in the 

 tissues of plants and animals are also neutral. Acids, therefore, 

 unless counteracted, act as poisons ; and organisms would be in 

 perpetual danger of perishing from their own products if their 

 acids were not continually neutralised. There are other products 

 of the plasm-machinery, however, which, by combining with the 

 acids, not only avert the danger, but form salts highly beneficial 

 to the organism, especially in regard to the action of muscles, 

 nerves, or glands. By this means, again, life is preserved in 

 equilibrium. 



Other products of the chemical machinery are substances 

 forming the framework by which the plastic plasm builds itself 

 up into definite structures, The machinery operates in two ways. 

 It works up into additional plasm the absorbed materials suitable 

 for growth, and so increases in mass; and it works out of its 

 wheels, so to speak, the substances it cannot utilise in that way, 

 and which would clog its movements if not extruded. This 

 results in precipitations of those substances, away from the 

 central points of activity. Every small mass of plasm con- 

 sequently forms a film at its surface. The plasm, enclosed in its 

 surface film, may be a nucleus or a free cell. When a larger 

 plasm mass divides up into a number of cells, by reason of forces 



