516 CONSTRUCTIVE AND DESTRUCTIVE METABOLISM 



protection play a most important part in determining the character and 

 course of metabolism : thus starch remains intact in the presence of an 

 abundance of sugar, and probably every form of reserve-food-material 

 can be protected by the presence of a suitable nutrient substance. It 

 is, on the other hand, of the utmost importance that in case of need 

 the plant should be able to utilize as much as possible of the nutrient 

 material at its disposal (Sect. 78), so that a substance may be reassimilated 

 under such circumstances which normally remains permanently aplastic. 

 Similarly the fact that a substance can re-enter into metabolism does 

 not necessarily show that its temporary permanence is due to a balance 

 existing between the processes of disintegration and reconstruction, although 

 it is always possible that the apparent constancy of a product may be 

 attained by these means. 



The relations between mass and chemical action are of the utmost 

 importance in the regulation of metabolism, for by the continual removal 

 of the products by diosmosis, metamorphosis, or combination, a feeble 

 chemical action may be carried to completion, and hence by such means 

 the plant is able to stop or continue a given metabolic process according 

 to its needs l . The gradual decomposition of the passively secreted tannate 

 of methyl-blue affords an immediately evident example of a reaction of 

 this kind, and by similar means a salt of the strongest acid may be 

 completely decomposed by the weakest free acid. Trifling and hardly 

 perceptible reactions or dissociations may in this manner produce results 

 of altogether disproportionate magnitude. The removal of the products 

 is however due to the vital activity, and the latter frequently also creates 

 the partial reaction or molecular dissociation which forms the necessary 

 preliminary to any such action as mentioned above 2 . 



Indeed physiological regulation is primarily due to the direct reaction 

 of the organism, as for example when a deficiency of a substance excites 

 its production, and it is only by such means that any correlation of growth 

 is possible or that the formation of diastase can be regulated in Penicillinui. 

 Similarly the conversion of starch into sugar may be inhibited by an 

 accumulation of the latter which is insufficient to stop diastatic action, 

 so that we are here dealing not with a direct chemical action but with 

 a physiological reaction (Sect. 91). Moreover in the selection of food- 

 substances during metabolism chemical relationship is by no means of 

 primary importance (Sect. 67). 



1 Pfeffer, Osmot. Unters., 1877, p. 163; Oxydationsvorgange in lebenden, Zellen, 1889, p. 463. 

 Cf. also Sect. 22. The relations between mass and chemical action were first clearly recognized by 

 Eerthollet. Cf. Ostwald, Grundriss d. allgem. Chemie, 1890, 2. Aufl., p. 289. 



2 On the special properties of the cell, cf. Sect. 7 seq. ; diosmosis, Chap, iv; the importance of 

 surface tension- energy, Sect. 12. The osmotic pressure exercises but little effect. Cf. Ostwald, 

 Allgem. Chemie, 1891, 2. Aufl., Bd. i, pp. 1014, 1045. On reactions in confined spaces, cf. Liebreich, 

 Zeitschr. f. physik. Chemie, 1890, Bd. v, p. 536; Budde, ibid., 1891, Bd. vrr, p. 600. 



