Washburn, Literary Notices. 591 



unless we are willing to suppose tliat we can linow something about the con- 

 sciousness of animals. 



However, putting aside this diiJiculty, we may consider what our author has 

 to say about the development of the psychic, when its existence has been 

 guaranteed by the presence of association. There are two laws, he tells us, 

 which govern the association of stimuli. The first of these is that if the 

 combined action of several stimuli is at the outset necessary to produce a 

 certain reaction, after this combination and its resulting reaction have been 

 many times I'epeated, one of the stimuli assumes predominance and is able, 

 alone, to set off the motor response. The other law Bohn calls that of 

 association by similarity : it states that the characteristics common to a 

 class of objects become the stimuli which cause reaction, the essential stimuli, 

 so that an animal reacts in the same way to a whole class of objects whose 

 individual differences produce no effect. It is doubtless the reviewer's fault, 

 but these two laws do not seem quite fundamentally distinct. It might be 

 supposed that when, according to the first law, one stimulus assumes the 

 predominance in a group, various causes may operate to bring it into 

 ascendency, and that one of these causes may be the frequency of its occur- 

 rence, if it is a characteristic common to a class, as compared with the infre- 

 quent occurrence of any given individual characteristic ; thus the second 

 law would be a special case under the first. But this is not Bohn's idea. 

 He supposes that in the case of the first law all the stimuli in the group 

 have been at the start effective stimuli : the reaction fails if any one of them 

 is lacking. In the case of the second law, the stimuli which represent the 

 individual characteristics are not effective even at the outset. "The simpli- 

 fication is made at the origin : many elements do not succeed in entering 

 into the association." This being so, it is not apparent why the second law 

 should be called a law of association at all. If a hermit crab acts toward 

 a wooden ball as it acts toward a shell, and one grants that curvature of a 

 solid surface is the only effective stimulus in both cases, it is impossible to 

 see where there has been any association of stimuli. We should not speak 

 of association if a totally deaf animal reacted in the same way towards an 

 object making a sound and the same object silent. 



It is evident, Bohn points out, that among the lower invertebrates the 

 formation of associations must be very limited on account of the small 

 number of sensational elements that are available. What he calls "the first 

 psychic revolution" occurs with the higher development of the eye, which 

 furnishes a far greater variety of associable elements. At various points in 

 his argument the author lays stress on the paramount importance of the 

 sense of sight for mental development. Bvit he seems to regard its signifi- 

 cance as consisting chiefly in the multiplicity of sense discriminations which 

 the perfected eye makes possible ; whereas a deeper meaning lies in the fact 

 that the eye is the great "distance receptor," and as such serves the purposes 

 of association as no organ whose stimulation directly affects life and death 

 can do. The second "psychic revolution" occurs with the development of the 

 cerebral hemispheres. In these the results of even a single stimulation may 

 be preserved and become effective to determine future reaction : thus we 



