504 CONSTRUCTIVE AND DESTRUCTIVE METABOLISM 



origin of these zymogens i.s entirely unknown. Both aerobic and anaerobic 

 plants produce enzymes, and the non-formation of these substances by 

 aerobic organisms in the absence of oxygen affords no proof that they are 

 oxidation-products l . 



Changes in the rate of production. Liborius and Fermi 2 have both shown that 

 the production of proteolytic ferments as well as of invertin and other enzymes is 

 dependent upon the cultural conditions, for the absence of proteids, the addition 

 of quinine, antipyrin, &c., or subjection or a high temperature may partially or 

 entirely inhibit the process of their secretion. This result appears to be often 

 induced by unfavourable cultural conditions, but in many cases no enzymes are 

 formed although growth remains active. An excess of the products of enzymatic 

 action may also constitute an inhibitory stimulus. Thus Katz 3 found that Penicil- 

 lium glaucum forms no diastase when more than i*- per cent, of cane- or grape- 

 sugar is present in the nutrient fluid. Bacterium megatherium behaves similarly, 

 whereas Aspergillus niger produces traces of diastase even in a 30 per cent, solution 

 of sugar. Penirillium ceases to form diastase when growing actively in sugar- 

 solution, but not during active or feeble growth upon 3 per cent, or 10 per cent. 

 solutions of quinolic acid. Hence it is evident that we are dealing with a specific 

 stimulatory action, which is more powerful in the case of dextrose and cane-sugar, 

 and less so in that of maltose and lactose. Aspergillus niger reacts in a similar 

 manner but not so strongly, and similar relationships will probably hold good 

 for other ferments as well, although a stimulus which suppresses the formation of 

 diastase need not necessarily affect the production of other ferments 4 . 



It is not the mere excretion of ferment which is affected by the concentration 

 of the nutrient solution, for the diastatic activity of the excreted ferment often 

 becomes markedly influenced only in highly concentrated sugar solutions 5 . Direct 

 experiments, moreover, have shown that no diastase is present within plants of 

 Penicillium grown on a 2 per cent, solution of sugar. 



Certain fungi and bacteria, however, produce diastase even in sugar solution, 

 although Wortmann's results are not trustworthy, since they were obtained with 

 a mixture of bacteria". 



In the case of Phanerogams the accumulation of sugar seems only to depress 



1 See Griiss, Landw. Jahrb., 1896, Bd. xxv, p. 425. 



2 Liborius, Zeitschr. f. Hygiene, 1886, Bd. i, p. 156; Fermi, Centralbl. f. Bact.. 1891, Bd. x, 

 p. 465 ; 1892, Bd. xn, p. 714; 1895, Abth. ii, Bd. I, p. 482 ; Fernbach, Ann. d. 1'Inst. Pasteur, 

 1890, T. iv, p. 641. Cf. Fliigge, 1. c., Bd. I, p. 209 ; Beyerinck, Centralbl. f. Bact., 1895, Abth. ii, 

 Bd. I, p. 226. 



3 [Katz, Die Regulatorische Bildung von Diastase durch Filze, Jahrb. f. wiss. Bot., 1898, 

 Bd. xxxi, p. 599.] See Sitzungsb. d. Sachs. Ges. d. Wiss., 1896, p. 513. 



* Beyerinck (Aliment photogene, 1891, p. 23, Sep.-abdr. a. Archives Neerlandaises, T. xxiv) 

 observed that in a few luminous bacteria the secretion of diastase may be depressed by the addition 

 of sugar but not that of proteolytic enzymes. 



5 For literature see Schleichert, Die diastat. Fermente, 1893, p. 45; A. Meyer, Starkekorner, 

 I ^95P-66; Griiss, Landw. Jahrb., 1896, Bd. xxv, p. 399; Tammann, Zeitschr. f. physik. Chemie, 

 1889, Bd. in, p. 32. 



6 Biisgen, Ber. d. Bot. Ges., 1885, p. Ixvi; Krabbe, Jahrb. f. wiss. Bot., 1890, Bd. xxi, p. 564; 

 "Wortmann, Zeitschr. f. physiol. Chemie, 1882, Bd. vi, p. 316. 



