Page:Mind (New Series) Volume 15.djvu/434

420 NEW BOOKS. differentiation and heredity. The conclusions drawn from the experi- ments on the tropisms of animals challenge criticism most loudly. The author tells us : "I have tried to find the agencies which determine un- equivocally the direction of the motion of animals " and that " I consider a complete knowledge and control of these agencies the biological solu- tion of the metaphysical problem of animal instinct and will ". His. experiments seem to prove that some lowly animals almost invariably move towards the principal source of light parallel to the direction of the strongest rays, more particularly of the visible rays of short wave length, while others have the opposite tendency (positive and negative helio- tropisms) ; that others tend to mount against gravity (geotropism), and others to keep their bodies in contact with surfaces or edges of solid bodies (stereotropism). Two or more of these tendencies are combined in some creatures, and the author jumps to the conclusion that all the movements of these animals are unequivocally determined by the physical agencies that play upon them, that " by the help of these causes it is possible to control the ' voluntary ' movements of a living animal just as securely and unequivocally as the engineer has been able to control the movements in inanimate nature. What has been taken for the effect of ' will ' or ' instinct ' is in reality the effect of light, of gravity, of friction, of chemical forces, etc." ; that "however complicated they may be, the ' voluntary ' movements of annuals are nevertheless, . . . always unequivocally determined only by such circumstances as determine also the movements of bodies in inanimate nature ". He regards not only " will " but also " instinct " as mystical conceptions. Yet if we regard an instinct as a congenital disposition of the nervous system which deter- mines a certain mode of reaction to certain stimuli, the conception is purely material and might m be thought acceptable to the crudest ma- terialist. But Prof. Loeb is so blindly zealous to reduce the living organism to the plane of the billiard-ball that he grudges any credit to the structure of the organism. He should remember that even the billiard-ball only rolls because it is round, and that its path across the table is determined not wholly by the cue and the table but also by its own structure and properties, and that in a similar manner, even if we hold by psycho-physical materialism, we must regard the movements of animals as determined not unequivocally by the physical impressions made upon them, but as reactions upon those impressions, of which the form depends largely upon the structure of the animal and especially of its nervous system. The author asserts that he has proved the helio- tropism of animals to be identical with that of plants, and concludes that,, since plants have no eyes and nervous systems, therefore the eyes and the nervous system of the moth have nothing to do with its flying into the candle flame, and that this occurs merely because its protoplasm is positively heliotropic. The conclusion may possibly be true, but the reasoning is certainly false. By parity of reasoning men gather round the fire on a cold evening merely because their protoplasm is positively heliotropic. The author does well to deprecate some of the extremely anthropomorphic interpretations of the behaviour of lower animals, and if he contented himself with descriptions of observed effects he would be in a strong position ; but he makes positive denials of the psychic life even more reckless than the assumptions in regard to it which he com- bats. Doubt is thrown upon even his more legitimate conclusions by- some of his own observations, e.g. of nothing is he more positive than that movement toward the light is a direct unequivocally determined effect of the light on the protoplasm of animals, yet he himself describes an experiment (p. 54) in which a number of ants seemed to become