258 THE POWER OF RESISTANCE TO EXTREMES 



mined whether the neutral salts do not exercise a poisonous action when 

 in still greater concentration. 



Since bacteria plasmolysed in a concentrated solution soon re-expand, 

 the injury produced in a strong solution of an innocuous substance can only 

 be due to the direct osmotic action of the latter. In this case, however, 

 solutions of high osmotic concentration are present both inside and outside 

 the protoplast, so that the conditions differ from those in a cell whose 

 turgor has been decreased or removed by transpiration. It is, however, 

 unknown whether different species always exhibit similar differences of 

 resistance in the two cases, although it is certain that no exact parallelism 

 exists between resistance to drying and resistance to plasmolytic solutions. 

 The injurious action of the latter in general increases as the concentration 

 rises, and although as usual the spores are most resistant, the vegetative 

 cells of many micro-organisms remain living in concentrated solutions 

 without growing for a few weeks or even months, whereas others die in a 

 few hours. De Freytag 1 found that anthrax bacilli died in two hours in 

 a nearly saturated solution of salt, but the spores not until six months, the 

 growth limit lying at a concentration of 7 to 10 per cent. Cholera bacilli 

 with a similar growth limit died in six to eight hours, but typhus bacilli 

 only after five months. 



Permanent plasmolysis always produces death sooner or later, and 

 this is accelerated by a rise of concentration in the case of cells resistant to 

 drying as well as in that of non-resistant ones. Different seeds, like other 

 organs, are unequally resistant, and thus some soon die in sea-water 2 , whereas 

 others are distributed by ocean currents 3 , and are either comparatively 

 resistant to the action of sea-water or possess relatively impermeable coats. 



PART V 



CHEMICAL AGENCIES 



SECTION 72. The General Properties of Poisons. 



Every substance which in larger or smaller doses produces, in virtue of 

 its chemical properties, functional disturbances ending ultimately in per- 

 manent injury or death can be classed as a poison 4 . Many organic and 



1 De Freytag, Archiv f. Hygiene, 1890, Bd. xi, p. 81. Cf. also Pettersen, ibid., 1900, Bd. xxxvn, 

 p. 3; Wehmer, Centralbl. f. Bact., 1897, 2. Abth., Bd. Ill, p. 209; Lafar, Technische Mykologie, 

 1897, p. 193; Schmidt-Nielsen, Biol. Centralbl., 1901, Bd. xxi, p. 68. 



a Cf. Thuret, Arch. d. sci. phys. et nat. d. Geneve, 1873, T. XLVII, p. 177. 



s Schimper, PHanzengeographie, 1898, p. 32. 



4 On the term 'poison' cf. Kobert, Lehrbuch d. Intoxicationen, 1893, p. 9; Kunkel, Handb. 



