304 BEHAVIOR OF THE LOWER ORGANISMS 



stimulation of a certain general character, — namely, to any condition 

 that interferes with the normal course of the life processes. On re- 

 ceiving an unfavorable stimulus that it has never before experienced, 

 the organism behaving on this plan is not at a loss for some method 

 of reacting ; it merely responds in the usual way, performing one move- 

 ment after another, till one of these relieves it of the stimulation, if this 

 is possible. 



Of course special circumstances may arise in which this general 

 method of reacting may be ineffective. If dropped into a strong chemi- 

 cal, Paramecium reacts in the usual manner, though this does not help 

 it. If the water containing a flat worm is heated, the animal goes 

 through, one after the other, almost every reaction it has at command, 

 though all are unavailing (p. 245). The difficulty, of course, lies in the 

 fact that under these circumstances nothing the organism can do is of 

 any avail, and a man in similar conditions would be equally helpless. 

 The infusorian and the flatworm, like the man, merely try everything 

 possible before succumbing. 



D. " Discrimination ' ' 



The effectiveness of reaction by continued varied movements in 

 preserving the organism depends upon several factors. One of these is 

 what is called in higher animals the power of discrimination, — that is, 

 the accuracy with which the tendency to react is adjusted to the injuri- 

 ousness of the stimulating agent. If an injurious agent resembles in 

 its first action a non-injurious one, so that the animal reacts in the same 

 way toward both, its behavior will not preserve it from injury. Using 

 the more subjective form of expression, if the organism does not discrimi- 

 nate between the first action of injurious and non-injurious agents, it 

 cannot react differently to them, until perhaps the injury has become 

 irremediable. The facts show that in both higher and lower organisms 

 the power of discrimination under weak stimulation is far from perfect. 

 Thus, in the sense in which we have used the term, Paramecium dis- 

 criminates acids from alkalies and salts, and these again from sugar. 

 But it does not effectively discriminate the first effects of different acid 

 substances, so that it swims into weak carbonic'acidj which is harmless, 

 and likewise into weak sulphuric acid and copper sulphate, which kill it. 

 It does not discriminate the first action of a 10 per cent sugar solution 

 from that of water, hence it swims readily into the sugar solution and is 

 killed by the osmotic action. In all these cases it does discriminate and 

 react to the injurious agent when its effect has become marked, but 

 injury has then already occurred and the reaction does not preserve the 



