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THE AMERICAN NATURALIST [Vol. XLIII 



same as Loeb's ' ' rntersdiiedsempfindlichkeit" and signifies re- 

 actions to changes in the environmental conditions. "II s'agit, 

 en effet, de reponses a des variations plus on moins brusques des 

 diverses forces du milieu exterieur" (p. 167). 



Consider in connection with the above statements from Bohn, 

 the following: In the table of contents of my book on the "Be- 

 havior of the Lower Organisms" (1906), we find the caption 

 Change of Conditions as a Cause of Eeaction. Turning to the 

 indicated chapter (XVII), as any one would naturally do who 

 desired to form a conception of my results on this matter, we 

 find that the second numbered paragraph begins : 



The most general cause of a reaction is a change in the conditions 

 affecting the organism. This has been illustrated in detail in the de- 

 scriptive portions of the present work (p. 293). 



Practically the entire chapter is taken up with an analysis 

 and discussion of variations in the environmental agents as 

 causes of reaction. In the descriptive portions of the work the 

 point is set forth most explicitly again and again. Taking the 

 account of Paramecium as a type, we find the following : 



It is clear that the cause of reaction is the change from o e 1 ltion 

 or temperature to another (p. 51). The animal, having been subjected 

 to certain conditions, becomes now subjected to others, and it is the 

 transition from one state to another that is the cause of reaction. This 

 is a fact of fundamental significance for understanding the behavior of 

 lower organisms 12 (p. 52). But as its movements carry the animal 

 from one region to another, the environmental conditions affecting it 

 are of course changed, and some of these changes in condition act as 

 stimuli, causing the animal to change its movements (p. 58). In the 

 reactions to mechanical stimuli, chemicals, osmotic pressure, heat and 

 cold, and powerful light, the avoiding reaction is caused by the transi- 

 tion from one external condition to another, by change in the intensity 

 of action of some agent (p. 78). Examination has shown us thai the 

 cause for this reaction is some change in the conditions (p. 108). 



For other organisms the point is likewise developed in detail 

 and stated with equal explicitness. Thus, for Amoeba: "The 

 cause of a reaction— that is, of a change in movement— is in 

 most cases some change in the environment" (p. 19) ; for Bac- 

 teria: "The reaction is caused as a rule by a change in the 

 environment of the organism" (p. 37) ; for the reactions of 

 Stentor to light: "all together, then, our experiments have 



