718 COMPARATIVE AND GENETIC PSYCHOLOGY 



ence from structure, from behavior, or from product. A basis for 

 this inference, that is, a test of the presence of consciousness, has, 

 therefore, to be found. 



There are two widely opposed doctrines concerning the nature 

 of this test. The first of these may be called the continuity doc- 

 trine. In its unmodified and most consistent form, it ascribes con- 

 sciousness to all living organisms, on the ground that life implies 

 consciousness. In other words, the continuity theory interprets 

 animal movements by their analogy with human conduct. Opposed 

 to this doctrine is the mechanistic theory, which conceives of all 

 plants and of the lower forms of animal life as mere mechanisms, 

 on the ground of their unvaried and perpetually recurring reac- 

 tions. The test of consciousness is, on this view, non-mechanical 

 that is, adaptive behavior. 



Upholders of the continuity theory have two arguments for 

 their doctrine that consciousness is a property of animal life. The 

 first is a metaphysical argument, based on that principle of con- 

 tinuity from which I have named the theory. Some animal organ- 

 isms, it is argued, have consciousness, and the forms of animal 

 life succeed so closely on each other that it is irrational to sup- 

 pose the sudden appearance of consciousness at any one stage; 

 hence it must have accompanied animal life from the first. The 

 second argument is empirical, not metaphysical in character. It 

 is based on a two-fold analogy of the animal with the human organ- 

 ism: the likeness of certain structures of animal bodies with those 

 of human bodies, and more important the similarity of ani- 

 mal activities to movements consciously performed by human 

 beings. This analogy is extended to the lowest forms of animal 

 life. "The Infusory," Binet says, "guides itself while swimming 

 about; it avoids obstacles; ... its movements seem to be designed 

 to effect an end. ... In short, the act of locomotion, as seen in 

 detached Infusoria, exhibits all the marks of voluntary movement." 1 

 After the same fashion are explained the movements of bacteria 

 toward grains of chlorophyl in a drop of water which contains no 

 oxygen, 2 the amoeba's rejection of foreign substances, 3 and the 

 movements of animals higher in the scale of life of echinoderms, 

 for instance from dark places into well-lighted ones. 4 



In all these cases, the underlying argument is the same: infu- 

 soria, bacteria, and amoebae, echinoderms and higher animals 

 perform acts like those which are voluntarily, or at any rate con- 

 sciously, carried out by human beings; therefore, infusoria and 

 the rest are conscious. The analogy is strengthened when to simi- 



1 The Psychic Life of Micro-Organisms, translation, Open Court Co., p. 46. 



2 Ibid. p. 32. 



3 Ibid. p. 41. 



4 G. H. Schneider, Der thierische Wille, chap, v, p. 164. 



