THE COMMONER METABOLIC PRODUCTS 451 



De Saussure proved that seeds lose in weight by respiration during germination, 

 and Proust made the first comparative analyses of germinated and dormant barley- 

 corns, from which important conclusions as to the formation of sugar from starch 

 were drawn 1 . De Saussure proved in the same manner that sugar and dextrin-like 

 substances are produced as the starch disappears during the germination of wheat, 

 and he showed that sugar is also formed when oily seeds germinate". 



Although the analytical methods employed were faulty, still a sound basis was 

 laid for the further researches of later authors, such as Hellriegel, 1855, Oudemans 

 and Rauwenhoff, 1859, &c. 



The microchemical methods now largely used were first systematically employed 

 by Sachs, who obtained by these means a general idea as to the metamorphoses 

 which plastic substances may undergo, and also as to their importance for trans- 

 location and for constructive purposes 3 . 



The results thus obtained as regards non-nitrogenous bodies still hold good, 

 although it is now known that a great variety of substances may be produced by 

 the decomposition of proteids. 



SECTION 78. The Commoner Metabolic Products. 



It is more convenient to discuss the relations of different substances 

 and groups of substances to metabolism than to study each separate 

 metabolic activity in detail, although the latter plan would be more desirable 

 from a physiological point of view were our knowledge not so incomplete. 

 Hence the economic importance of different substances does not concern 

 us here, nor can any complete account be given at present of those aplastic 

 materials whose importance in metabolism is unknown. It is beyond our 

 scope to do more than give the main facts and principles of metabolism and 

 to illustrate them by examples, while in dealing with different groups of 

 substances it must always be remembered that the same material may 

 subserve a variety of purposes, and that to attain a particular end bodies of 

 very heterogeneous chemical constitution may co-operate with one another. 

 Hence the distinction between formative, plastic, and aplastic materials 

 simply indicates very generalized metabolic characteristics, and does not 

 allow any sharp line of demarcation to be drawn between different 

 substances or groups of substances (Sect. 77). 



In addition to various proteids the living protoplast contains other 



1 De Saussure, Rech. chim., 1804, p. 16 ; Proust, Ann. d. chim. et d. phys., 1817, T. v, p. 342. 

 Berard (ibid., 1821, T. XVI, pp. 152, 225) performed similar comparative analyses on ripening fruits. 



2 De Saussure, Mem. d. 1. Soc. d. Phys. et d'Hist. Nat. d. Geneve, 1833, T. vi, p. 27 ; Bibl. 

 univ. d. Geneve, 1842, T. XL, p. 370. 



3 Sachs, Uber einige mikroskopisch-chemische Reactionsmethoden, Sitzungsb. d. \Vien. Akad., 

 1859, Bd. XXXVI, p. 5, and Keimung d. Schminkbohne, ibid., 1859, Bd. XXXVII, p. 57; Uber d. 

 Stoffe, welche das Material zum Wachsthum d. Zellhaute liefern, Jahrb. f. wiss. Bot., 1863, Bd. in. 

 p. 183. Cf. also Rochleder, Chem. ti. Physiol. d. Pflanze. 1X58. pp. 99, 147. 



G g 2 



