THE APPEARANCE OF LIFE 65 



upon certain organic substances, the carbo-hydrates, fats, and 

 the albuminoid substances in particular, causing fundamental 

 changes, and themselves undergoing transformations so slight 

 in character that some experimentalists have thought they are 

 not modified at all by their activity. Certainly the influence they 

 exert is entirely out of proportion to the amount of their own 

 substance that is altered and the enormous mass of substance 

 they transform. There is an exceedingly large number of these 

 ferments acting respectively on the carbo-hydrates {diastases) 

 on the fats {lipases) or on albumens. Each one possesses its 

 own specific action — decomposition, hydration, dehydration, 

 oxidation, reduction, coagulation, or dispersion, and though 

 simple, they suffice to displace, transform or break up complex 

 organic substances. Each ferment frequently has some counter- 

 ferment which neutralizes what it has accomplished ; some are 

 only active when associated with others which assist them ; 

 frequently they possess a reversible activity, and are capable 

 under certain circumstances of reconstituting the bodies they 

 have destroyed. 1 They are frequently poured into the body of 

 the organism by glands outside of which their action takes place, 

 but they also mix with other associated substances to form a 

 vital element, and their very presence suffices to stimulate the 

 activity of substances that would otherwise remain inert. 

 Through their agency, associated organic substances undergo 

 unceasing interchanges and reciprocal modifications in the 

 presence of the oxygen of the air and the water impregnating 

 them. The larger organic molecules break down, so to speak, 

 upon the others ; but it is the characteristic of life that in this 

 disintegration the more complex substances split up the simpler 

 and annex the broken-down fragments, so that the unceasing 

 process of decomposition is yet balanced by a building-up and 

 an actual increase of the substance brought into action. This 

 increase is called nutrition, and its natural consequence is 

 reproduction. 



Life, thus understood, is not the work of a single substance, 

 but rather a result of the reciprocal reactions of a certain 

 number of definite substances. These, moreover, are not 

 without individuality. They appear in a relatively small 

 number of groups, which in all living organisms seem to possess 

 the same fundamental chemical structure although they differ 



1 I, 664. 



