January 3, 1902. J 



SCIENCE. 



21 



has passed, tliat all of the reflexes belonging to 

 the segments of the body which are represented 

 by the portion of the cord severed can be ex- 

 ecuted. Rubbing of the skin causes scratching 

 movements of the hind legs, and the reflexes of 

 bladder, rectum and respiratory organs occur 

 in response to the appropriate stimuli. 



"According to the segmental theory," v^rites 

 our author, "there are only indifferent seg- 

 mental ganglia in the central nervous system, 

 and the different reactions or reflexes are due 

 to the different peripheral organs and the ar- 

 rangements of the muscles. The center theory 

 must remain satisfied with the mere problem 

 of localizing the apparent 'seat' of a 'function' 

 without being able to give the dynamics of the 

 reactions of an animal, as the latter depend in 

 reality upon the peripheral structiires, and not 

 on the structures of the ganglia. For this 

 reason the segmental theory alone will be able 

 to lead to a dynamical conception of the func- 

 tions of the central nervous system." 



In taking up the problem of instinct Pro- 

 fessor Loeb touches a field which he has made 

 distinctively his own; for no one has done so 

 much as he toward the analysis and explana- 

 tion of this type of action. He holds that 

 there can be no sharp separation of reflex ac- 

 tion from instinctive. The reflex visually is 

 the activity of a single organ, and the instinc- 

 tive act one in which the whole organism is 

 concerned. Instinctive actions are character- 

 ized by an apparent adaptation to a special 

 purpose, an adaptation to the circumstances 

 in which they occiir. For this reason there is 

 a strong tendency to regard them as results 

 of intelligence. For years Professor Loeb has 

 been studying, and, as it were, dissecting, in- 

 stinct after instinct in order to show the ab- 

 surdity of this conception. 



The fly that instinctively selects for the de- 

 positing of its eggs a substance on which the 

 larvse can feed does so not because it has a 

 faint notion of the utility of the action, or 

 even because it chooses so to do, but because 

 the chemical particles emanating from the sub- 

 stance stimulate it in such fashion as to cause 

 an orientation of its body in reference to the 

 source of the stimulus, and this orientation in 

 turn determines the movement toward the sub- 



stance. The whole is simply a mechanical prob- 

 lem; physics and chemistry serve to explain 

 the instinct. 



An insect comes within the range of vision 

 of a frog and is instinctively stalked, seized 

 and swallowed. In this event the visual stimu- 

 lus initiates a series of reflexes whose result is 

 the obtaining of food. There is no deliberate 

 choice, no intelligence in the action. The crus- 

 tacean or insect or worm that instinctively 

 moves toward a source of light does so, experi- 

 ments indicate, simply because the light forces 

 it -to take a certain orientation, just as the 

 chemical stimulus did in case of the fly. Once 

 having taken this position, there is only the 

 possibility of moving toward the source of 

 the stimulus. The 'orientation theory' is one 

 of Professor Loeb's chief contributions to the 

 explanation of instincts. It is based upon 

 the assumption that when a stimulus affects 

 synunetrical points of an animal's body un- 

 equally there is resulting inequality of mus- 

 cular activity on the two sides, and as a result 

 the organism is finally forced into that position 

 in which symmetrical points are equally 

 stimulated. Such a position is evidently at- 

 tained when the long axis of the body is par- 

 allel with the rays of light, for example, with 

 the head either toward or away from the 

 source of the light. From this position it is 

 clear the animal can move only toward or 

 away from the light. 



And again it is noticed that certain arthro- 

 pods and worms 'hide' in crevices. If we 

 study this action we learn that the animals 

 are able to remain quiet only when the body 

 is in contact with some object, and so long 

 as it is not in such a position the animal 

 moves about continuously. In the act 'hid- 

 ing' plays no part. The phenomenon is 

 merely the inhibition of movement by a 

 stimulus, it matters not whether the stimulus 

 be given by a board which really 'hides' the 

 animal or by a plate of glass which leaves it 

 fully exposed to view. And so one might go 

 on with the enumeration of simple instinctive 

 acts that appear to be guided by reason, but 

 whose careful study reveals only the influence 

 of certain environmental factors upon a defi- 

 nitely describable organic structure. 



