THE CHARACTERISTICS OF ORGANISMS ii 



mental fact that streams of matter and energy, such as food and 

 light, are continually passing into the organism, and that other 

 streams are continually passing out, for instance in the form of 

 carbon dioxide and heat. On the other hand, the comparison has 

 its weakness and possible fallaciousness; for it is too simple. It 

 does not do justice to the characteristic way in which the organism- 

 whirlpool acts on the stream which is its environment; it does not 

 do justice to the characteristic way in which the organism-whirlpool 

 gives rise to others like itself. No one who believes that higher 

 animals (at least) have a mental aspect that counts, can agree 

 that the organism is exhaustively described as "nothing but the 

 constant form of a turmoil of material molecules." And even if 

 the mental aspect be ignored, there remains as a fundamental 

 characteristic that the "constant form" is secured by organic 

 regulation from within. Life is nothing if not regulative. 



Biology has come nearer the crayfish since Huxley's day, and it 

 is profitable to linger over the fact that the living creature persists 

 in spite of its ceaseless change. As a matter of fact it persists 

 because of the self -repairing nature of its ceaseless change. Hence 

 we give prominence to this material flux. 



Metabolism of Proteins. — Proteins are nitrogenous carbon- 

 compounds that are present in all organisms, and, apart from 

 water, of which there is seldom less than 70 per cent., they con- 

 stitute the chief mass of the living substance. They are intricate 

 compounds, with large molecules, which are built up of groups of 

 amino-acids, i.e. fatty acids in which one of the hydrogen atoms is 

 replaced by the «wwo-group NH2. Proteins, such as white of egg, 

 or the casein of cheese, or the gluten of wheat, do not readily diffuse 

 through membranes; they occur, as will be afterwards explained, 

 in a colloid state, and although some, e.g. haemoglobin, the red 

 pigment of the blood, are crystallisable, they are not known in 

 a crystalloid state in the living body. Though relatively stable 

 bodies, proteins are continually breaking down and being built up 

 again within the cells of the body, partly under the direct influence 

 of ferments or enzymes. 



There are constructive, synthetic, upbuilding, or winding-up 

 chemical processes always going on in the living organism, which 

 are conveniently summed up in the word anaholism, applicable, of 

 course, to the synthesis of other carbon-compounds besides pro- 

 teins, notably to the formation of carbohydrates in the sunned 

 green leaf. There are also disruptive, analytic, down-breaking, 

 running-down chemical processes always going on in the living 

 organism, which are conveniently summed up in the word kata- 

 holism — applicable, of course, to other carbon-compounds besides 

 proteins, as, for example, to the breaking down of amino-acids into 



