CHEMOTAXIS AND OSMOTAXIS 347 



and probably other sulphur-bacteria as well 1 , while the comparatively insen- 

 sitive typhus- and cholera-bacilli 2 are strongly attracted by potato-sap. 



Increasing concentrations of neutral salts exert hardly any perceptible 

 chemotactic or osmotactic repulsion 3 upon Bacterium termo, but a strong 

 one upon Spirilhim undula, while the action upon other forms lies between 

 these extremes. Free acids produce repulsion in the case of Spirillum 

 undula even when very dilute, but alkalies only when somewhat more con- 

 centrated. Ether and alcohol 4 may in certain cases produce repulsion, 

 while the presence of oxygen dissolved at ordinary pressure from air is 

 sufficient to repel Spirillum undula and 6\ serpens. Sulphur bacteria and 

 other anaerobic bacteria react still more readily to oxygen, and in some 

 cases are so sensitive that the merest trace of oxygen produces repulsion, 

 although most bacteria are capable of positive chemotaxis in regard to 

 oxygen 5 . Since Bacterium termo has hardly any negative osmotaxis or 

 chemotaxis, motile forms penetrate concentrated solutions of sugar or 

 potassium chloride in abundance, whereas a slight concentration exercises 

 an osmotactic repulsion upon Spirillum undula. 



Flagellatae and Volvocineae. Many colourless Flagellatae react chemo- 

 tactically and osmotactically to various substances, and in general the 

 reactions resemble those of Bacteria 6 . Thus Bodo saltans, Trepomonas 

 agilis, and Hexamitus rostratus have about the same positively chemotactic 

 sensitivity as the most sensitive bacteria, whereas Hexamitus intestinalis 

 only reacts weakly, and Astasia proteus and Tetramitus restrains not at 

 all. So far as is known, the green Flagellatae show no positive chemotaxis, 

 apart from their aerotaxis 7 , whereas some of the Volvocineae are able to 

 respond with moderate activity to the chemical substances already 

 mentioned. 



Many substances which produce a phobotactic action upon Bacteria 

 induce a typical chemotactic reaction when presented to the above- 

 named Flagellatae 8 . The zoospores of Saprolegnia* behave similarly 



1 Miyoshi, Journal of the College of Science, University of Tokyo, 1897, Vol. x, p. 169. 

 3 Pfeffer, 1. c., p. 615 ; A. Cohen, Centralbl. f. Bact., 1890, Bd. vin, p. 164. 

 3 Pfeffer, 1. c., p. 621. 

 * Rothert, 1. c., p. 380. 



5 On ' Aerotaxis' or ' Oxygenotaxis,' cf. Bd. II, p. 582 footnote, and also Engelmann, Pfliiger's 

 Archiv, 1881, Bd. xxvi, p. 541 ; Beyerinck, Centralbl. f. Bact., 1893, Bd. XIV, p. 835; 1895, 

 Abth. ii, Bd. I, p. in ; Rothert, 1. c., p. 377. Oxygen exerts no chemotactic action on the sperms 

 of Ferns (Pfeffer, 1. c., 1884, p. 372) or upon the zoospores of Saprokgnia (Rothert, Cohn's Beitrage 

 z. Biol., 1892, Bd. v, p. 341 ; Stange, Bot. Ztg., 1893, p. 139). 



6 Pfeffer, 1. c., 1888, pp. 595, 615, 625. 



7 On the stimulating action of oxygen upon Euglena viridis see Aderhold, Jenaische 

 Zeitschr. f. Naturwiss., 1888, Bd. XXII, p. 314. 



8 Cf. Rothert, Flora, 1901, p. 388. 



9 Rothert, 1. c., p. 388. For substances acting as stimuli see Stange, Bot. Ztg., 1890, p. 124. 



