j3« LIFE : OUTLINES OF GENERAL BIOLOGY 



clearer, firmer biology. For the biologist has questions of his owi to 

 ask and answer, which are beyond the scope of chemistry and 

 ph}'sics as we know them to-day. For him the living organism is an 

 individuality — not a vat or an engine. It is an integrate, suffused 

 with awareness and with some measure of endeavour. In many cases 

 it has clearly a mind of its own. In its reproduction, development, 

 and purposive agency, in its heredity, variation and evolution, the 

 organism transcends chemistry and physics. There are treasures in 

 its sea which cannot be caught in the meshes of the chemical and 

 physical net. The organism is alive. 



THE CHEMISTRY OF THE ANIMAL BODY 



I. THE FOOD AS A SOURCE OF ENERGY.— In the chapter of 

 this book which deals with the living cell, it is explained that the 

 energy of the animal body has its source in the chemical reactions 

 which go on there, and that by far the most important of these 

 reactions are oxidations. In typical cases, the carbon of the food is 

 oxidised to carbon dioxide, and the hydrogen to water. It will be 

 explained later that the animal has certain particular chemical 

 requirements, but as iar as energy-output is concerned the essentials 

 are that there should be a suftkient supply of organic food-material 

 (containing carbon and hydrogen), and sufficient oxygen to combine 

 with it. These, it may be recalled, are also the chemical require- 

 ments of the internal-combustion engine. 



Just before the French Revolution, Lavoisier had shown that 

 a candle was able to give out energy — light and heat — because it 

 oxidised carbon to carbon dioxide; he went farther and, aided by 

 the great physicist Laplace, showed that the same thing was true 

 of the animal body. His apparatus was rough and ready, and he 

 failed to avoid several pitialls; but he successfully proved his main 

 points. He could fmd out how much carbon an animal burnt in a 

 given time, by measuring the amount of carbon dioxide which it 

 breathed out; and at the same time he measured the amount of heat 

 produced by the animal, and compared these figures with the amount 

 of heat generated by an equivalent amount of carbon burnt in a 

 laboratory experiment. He found that nearly the whole of the 

 heat of the animal's body was due to the combustion of carbon. He 

 also knew that some of the oxygen used up combined with hydrogen, 

 but it was not till somewhat later that Dulong and Depretz were 

 able to draw up satisfactory balance-sheets in which the amounts 

 of oxygen used up, of carbon dioxide and water produced, and of 

 energy evolved, corresponded reasonably well. In the meanwhile, 

 however, Lavoisier had found that the body uses up far more 

 oxygen when it is performing any sort of extra work — muscular 



