32 ,-,;. t .. .SIQtflFIQANCE OF FOODSTUFFS 



The discovery by Schmiedeberg and Bunge in 1876 of the synthesis 

 of hippuric acid from benzoic acid and glycocoll in the tissues of the 

 kidney, 1 disposed of this untenable distinction, and while we are cer- 

 tainly to be regarded as primarily parasitic upon the vegetable and 

 lower orders of the animal kingdom, yet we are not so unable to create 

 constituents of living matter, as earlier investigators imagined. We 

 know now that animal tissues can perform a multiplicity of syntheses 

 whereby constituents of protoplasm are made which the food does not 

 contain preformed. It will be found, however, to be a general charac- 

 teristic of syntheses carried out in animal tissues, that the storage of 

 energy or heat-value which is accomplished thereby is usually small, 

 whereas in green plants syntheses are accomplished which involve the 

 locking up, for longer or shorter periods, of very large quantities of 

 energy; for eons as in coal deposits, or for the brief period of a single 

 winter as in the seeds which consume their stored-up energy when 

 they germinate in the spring. 



The reason for this distinction is not far to seek. The green plant 

 has an inexhaustible reservoir of energy upon which to draw; the 

 radiant energy of the sun; and the energy which is locked up in the 

 starches, fats and proteins, which plants synthesize from the most 

 elementary products of combustion, is derived in the long run from the 

 sun. The animal has no comparable capital to draw upon, and if an 

 animal is to perform a synthesis involving absorption of heat or energy, 

 it can only do so at the expense of its current account, that is to say 

 by the degradation of its own tissues or food reserves. On the whole, 

 therefore, and with the exceptions noted, green plants are the prime 

 conservers of energy, while the function of animals is to dissipate it 

 again. The whole fever and bustle of life upon the earth is therefore 

 none other than a transitory phase through which continually passes 

 a minute fraction of the colossal outpourings of solar energy. 



THE CONSERVATION OF MATTER. 



Whatever may be the relative efficiency of different types of proto- 

 plasm as storers of energy and creators of living matter, they are all 

 alike subject to the law of the Conservation of Matter. 2 That is to say, 

 although an animal or plant cell may create new chemical compounds ; 

 new permutations and combinations of the chemical elements, it cannot 

 create new elements. All of the carbon in its tissues must have been 

 derived, for example, from carbon from without. If an animal gives 

 off nitrogen in the form of urea, it must either take up fresh nitrogen 

 from without, or else its tissues must remain permanently poorer in 

 nitrogen. 



1 Thai this synthesis occurs in some organ or tissue of the body had been recognized 

 by Wohler as early as 1824. 



2 The applicability of the law of the Conservation of Matter to living organisms was 

 first demonstrated by its discoverer, the French chemist Lavoisier (1743-1794), and 

 subsequently confirmed in detail by Licbig (1803-1873). 



