45 CONSTRUCTirE AND DESTRUCTIVE METABOLISM 



but quantitative estimV.ions are possible only by macrochemical methods, and 

 these may enable deductions to be made for which qualitative microchemical 

 methods afford no sure basis. 



The facts obtained by these means when properly interpreted, and when 

 full attention is paid to the special properties of the living organism, may enable 

 a certain insight to be gained into the invisible processes which lead to the 

 formation of visible end-products. No general methods of investigation and 

 experimentation can be given which will be applicable to all cases, for the 

 manner in which a given problem is attacked should be adapted to the nature 

 of the phenomena for which an explanation is required. 



An account of certain of the physiological applications of machrochemistry 

 are given by Hoppe-Seyler, Handbuch der physiol.-chem. Analyse, 1893; J. Konig, 

 Unters. landw. u. gewerblich wichtiger Stoffe, 1891 ; Dragendorff, Qual. u. quant. 

 Analyse d. Pflanzen, 1842, and in the special works given. A general summary 

 of microchemical methods is given by A. Zimmermann, 1892, Mikrotechnik 

 (translated by Humphreys). Physiological methods, such as when the reactive 

 power of another organism is used as a test for the presence of a given substance, 

 oxygen by means of bacteria, malic acid or cane-sugar by antherozooids ', are 

 of great importance and may probably be employed to a greater extent than at 

 present, for by these means an approximately accurate quantitative determination 

 is possible, while at the same time the precise point at which a particular substance 

 is evolved can be observed. 



The chemical properties of the substances found in plants are described in 

 hand-books of chemistry, and also by Husemann in Die Pflanzenstoffe, 1882-4; 

 Ebermayer, Physiol. Chemie, 1882; Tollens, Handbuch der Kohlenhydrate, 

 1888-95. The special literature concerning the specific composition of different 

 plants and the changes which occur under varying cultural conditions and at 

 different stages of development have already been mentioned, but a detailed 

 summary of the special literature upon these points, however desirable it might 

 be, would be out of place here. In Konig's Chemie d. Nahrungs- und Genuss- 

 mittel, 1889, 3. Aufl., no attention is paid to physiological considerations. A few 

 points regarding the chemical composition of fungi and bacteria are given by 

 Zopf, Pilze, 1890, p. 117; Fliigge, Mikroorganismen, 2. Aufl., 1896, Bd. i, p. 93; 

 Marschall, Centralbl. f. Bact., 1897, Bd m, p. 154. 



Historical. Even in the earliest times, the fact was recognized that plants 

 are able to form substances which are not present in their food 2 , but it was 

 only at a much later date that precise determinations were made of any of the 

 metamorphoses which the absorbed substances may undergo. Thus Rollo pointed 

 out that sugar is formed during the germination of barley, and Senebier showed 

 that the oil and starch in seeds act as stored food-material from which various 

 substances are produced on germination, which process he compared to fermentation 3 . 



1 Pfeffer, Unters. a. d. Bot. Tnst. z. Tubingen, 1884, Bd. I, pp. 413, 432 ; 1888, Bd. II, p. 633. 

 a Cf. Sachs, History of Botany (Garnsey and Balfour), 1890, p. 480. 



* Rollo, Ann. d. chim., 1798, T. XXV, p. 40; Senebier, Physiol. veget., 1800, T. Ill, p. 406. 

 Cf. also de Candolle, Physiol., 1833, T. I, pp. 170, 266. 



