Editorial. 1 39 



actions whose direction is determined by differences in intensi- 

 ty of illumination. The former he calls phototaxis, the latter 

 photopathy. Photopathy is held to be due to the fact "that 

 increased brightness causes a movement forwards, that a dimin- 

 ution of brightness causes a movement backwards, or vice versa, 

 thus resulting in an accumulation of the organisms in the darker 

 •or lighter parts of the field." (1. c. p. 210.) Phototaxis on the 

 •other hand "includes that active migration of organisms whose 

 direction is determined by that of the rays of light" (p. 180). 

 In elongated organisms Davenport thinks that phototaxis is 

 •due to the difference in intensity of illumination of the two sides 

 of the organisms (p. 209), while in Amoeba he thinks it possible 

 that the direction taken by the ray in passing through the or- 

 ganisms is the determining factor (p. 210). Yerkes' holds, 

 with Holt and Lee, that both phenomena are due in some way 

 to the intensity of the light, and classes as taxis those reactions 

 in which the direction of movement is determined by orienta- 

 tion, while -pathy includes reactions in which the movement "is 

 not definitely directed through the orientation of the organism." 

 This distinction doubtless indicates the real observational source 

 •of the attempt to separate two great classes of reactions, and 

 •does not attempt to make the definition outrun the known facts. 

 Kinesis is a term which seems to have been first used by 

 £ngelmann^ for the increase or decrease of activity produced by 

 •certain agencies. The fact that certain bacteria increase or de- 

 •crease movement in the light he called photokinesis. Rothert 

 (/. c, p. 374) accepted the term kinesis for such changes in the 

 amount of activity produced by chemicals, calling this chemo- 

 kinesis. Loeb^ had observed similar phenomena and applied to 

 them the German word Unterschiedsempfindlichkeii. Gar key,* 

 Nworking with Loeb, later substituted the term kinesis for the Ger- 

 man word. The term UnterscJiiedsempfindliclikeit, signifying lit- 

 erally sensitiveness to differences, might well include much more 

 ihan a mere increase or decrease of activity ; it could properly 



'Mark Anniversary Volume, 1903, p. 361. 

 '^Arch.f. d.ges. Physiol., 30, 1882. 

 ^Arch.f.d.ges. Physiol., 54, 1893, P- '^l- 

 ^^Am. Journ. Physiol., 3, 1900, p. 29. 



