CHEMICAL CONSTITUTION AND POISONOUS ACTION 271 



particular animal, for this leaves uncertain the concentration needed to act 

 upon the responding cells and cell-elements in order to produce the effect 

 observed l . 



In supra-maximal concentrations of poison an organism may be injured and 

 die either rapidly or after a very long time, according to the nature of the poison 

 and its degree of concentration. This latter behaviour, which Overton 2 terms a 

 progressive action, is not peculiar to the action of poisons. Transitory exposure to 

 high temperatures or to the action of poisons may alike cause gradual death on 

 the subsequent restoration to optimal conditions. This may even occur when no 

 poison remains in the cells, although the retention of a portion of the poison may 

 naturally cause the injurious action to continue for some time. 



SECTION 75. The Influence of Chemical Constitution on Poisonous 



Action. 



It is easy to understand why acids and alkalies should act as poisons 

 to all plants, although owing to our ignorance of the physical and chemical 

 constitution of the protoplasm we are in most cases unable to predict 

 whether a substance of known chemical composition will act as a poison. 

 Hence actual experiment is usually necessary to determine whether any 

 material is poisonous, nutritious, or indifferent. The fact that different 

 protoplasts respond dissimilarly is sufficient to show that the protoplasm 

 varies more or less in its physical character and chemical composition. 

 Experiment has shown that the nutrient value and also the poisonous 

 action of allied chemical substances may differ widely, while dissimilar 

 substances may be physiologically equivalent in the above respects 3 . 



Hence the physiological value of a substance may be considerably 

 modified by a slight change of molecular structure, whereas similar changes 

 involving substitution, rearrangement, or polymerization in two different 

 compounds do not always result in corresponding alterations of their 

 physiological action. For instance, the poisonous character of organic com- 

 pounds is usually but not always increased by the addition of chlorine atoms 

 or nitro groups. Further, the substitution of hydroxyl, ethyl, or methyl for 

 hydrogen, or the introduction of amido groups, increases the poisonous action 

 in some cases, but decreases it in others. The members of the alcohol series 

 become more poisonous as the molecular weight increases, but this is not 

 always the case in such series. The poisonous action is also increased when 

 the introduction of a carboxyl group renders a substance acid or increases its 



1 Cf. Overton, Vierteljahrsschrift d. Naturf. Ges. in Zurich, 1899, Bd. XL1V, p. 128 ; Kunkel, 

 Toxicologie, 1899, p. 4. 



2 Overton, 1. c., p. 128. 



3 For details see Loew, System d. Giftwirkungen, 1893, pp. 44, 92, 129; Kunkel, 1. c., 

 pp. 391,402 seq. ; Overton, I.e., p. 124; True and Hunkel, Bot. Centralbl., 1898, Bd. LXXVJ, 

 p. 398 (phenol) j \Vehmer, Chemiker-Zeitung, 1897 (benzoic acid). 



