CHEMOTAXIS AND OSMOTAXIS 353 



also inhibited in various ways. Possibly the unequal distribution of the materials in 

 the cell may act as a stimulus, which will be maintained so long as a difference of 

 concentration exists on the two sides. 



Many bacterial protoplasts re-expand rapidly or slowly in plasmolysing solutions, 

 but others not at all 1 . These properties are not constant, however, and specific 

 peculiarities are often shown in regard to particular substances. The two bacteria 

 used by Massart behaved similarly on the whole, although asparagin repelled Bacillus 

 megatherium as strongly as potassium nitrate, but Spirillum undula not at all in the 

 concentrations used. This may be due to the especially rapid penetration of Bacillus 

 megatherium by asparagin ; but, for the reasons given, it is difficult to form a final 

 judgement. 



Many organisms show no negative osmotaxis when placed in solutions which 

 strongly plasmolyse them 2 . On the other hand, Massart found that Tetramitus 

 rostratus showed negative chemotaxis, although it has the power of rapidly accommo- 

 dating itself to concentrated solutions without its power of movement being affected. 

 Hence Fischer is hardly justified in concluding that the production or non-production of 

 plasmolysis indicates the presence or absence of a capacity for osmotactic reaction. 

 The causes which overcome or antagonize repulsion are not necessarily always the 

 same, and repulsion, like chemotaxis, may often be produced by solutions in which the 

 organism is capable of continued existence. It depends upon the properties and 

 power of accommodation of the organism whether the transference to a concentrated 

 solution hinders or inhibits the power of movement, and whether death ensues rapidly 

 or gradually. 



As the result of the attraction and repulsion, organisms of different sensibility 

 collect in zones at variable distances around the mouth of the capillary tube from 

 which the concentrated solution is diffusing. The gradual dilution caused by diffu- 

 sion, together with the accommodation of the organisms and the consumption of oxygen, 

 may cause the organisms in two zones to change places, or may induce the exit from 

 the capillary of forms which had previously penetrated it 3 . Excreted products of 

 metabolism may also produce attraction, and, according to Jennings 4 , the crowding 

 together of Paramaecium is due to the chemotaxis exerted by the excreted carbon 

 dioxide. 



Since these reactions may be produced either in a tropic or in a phobic 

 manner, direct experiment is necessary to determine the detailed character 

 of the reaction. The antherozoids of Ferns, Mosses, and Selaginella, 

 certain Flagellatae, and the zoospores of Saprolegnia, show positive and 

 apparently also negative chemotaxis ; but it is not certain whether the 



1 Cf. A. Fischer, Vorlesungen ii. Bacterien, 1903, 2nd Ed., pp. 24, 116. On the regulation of 

 turgor see H. v. Mayenburg, Jahrb. f. wiss. Bot, 1901, Bd. XXXVI, p. 381. 



3 Fischer, 1. c., p. 116. 



3 For details see Pfeffer, 1. c., 1888, p. 639 ; 1884, p. 472. Also Massart, Bull, de 1'Acad. royale 

 de Belgique, 1891, 3" ser., T. xxii, p. 157; Beyerinck, Centralbl. f. Bact., 1893, Bd. xiv, p. 827 ; 

 Abth. ii, 1895, Bd. I, p. in ; 1897, Bd. Ill, p. I ; Yegounow, Arch. d. sci. biol. de 1'Inst. imper. 

 de medecine de St. Pe'tersbourg, 1895, T. in, p. 381 ; Centralbl. f. Bacteriologie, 1898, Abth. ii, 

 Bd. IV, p. 97. 



* Jennings, Journal of Physiology, 1897, Vol. XXXI, p. 318. Cf. also Pfeffer, I.e., 1888, p. 619. 



PFEFFER. IH 



