390 HAVE FISHES MEMORY. 



we notice can be adequately explained by our physiological knowUMlge. 

 But the act does not always take so slow a course. It appears that 

 the frog sometimes responds more readily to irritations; that he some- 

 times advances upon the worm more alertly than in the above descrip- 

 tion; that he turns his head at the first movement made by the worm. 

 Hunger, the prevailing temperature, above all the frog's condition 

 after he has taken his first bite of food, increase his sensitiveness. 

 Then he eats greedily as much as he can lay hold of. On what this 

 state of heightened excitability depends has not been determined. In 

 this more sensitive condition a new element is observal)le. The frog 

 needs no constant stinudus. Having once responded to the irritation, 

 he goes on executing a series of acts calculated to serve a (h'Hnitc pur- 

 pose. He l)egins to crawl after the escaping worm: he chases his prey. 

 Obviously a new element has supervened. The earlier sensation con- 

 tinues in operation, and calls forth action adapted to bring about an 

 intended result. 



Numerous experiments made b}' physiologists ha\e proved tiiat 

 besides a certain intensity of the irritation, a variety of oth«u- condi- 

 tions must be fulfilled in order to produce reflexes. E([ually these 

 experiments have demonstrated that in certain circumstances reflexes 

 may be inhibited by the central system of nerves in animals equipped 

 with a brain. We are not defiling with uncertainties, nor ar(> we 

 setting up a hazardous h^^Dothiisis, when we assume that the taking 

 of food may be inhibited when other irritations — of an optical nature, 

 for instance — are stronger than those exerted by the food. 



Though in the present state of science we are far from taking account 

 of all the circumstances that induce the higher animals to feed, still it 

 is known that the component elements can be analyzed, and that the 

 main concern is the intensity of the optical, chemical, etc., stimulus 

 issuing from the food, the disposition of the body when the stimulus 

 is put into operation, and the inhibitive influences at work at the time. 



Fishes approach their food only if other sense impressions of great 

 vividness are excluded. If they are disposed to eat it, hunger, the 

 quality, and perhaps the electricity of the air and the water play a dis- 

 tinct part, and, above all, if the general behavior of the food is sucli 

 as to exert a stimulus of the proper character and of suflScient intensity 

 to call forth the reflex act of eating. If these conditions are not ful- 

 filled — if, for instance, the artificial bait in some important particular 

 fails to resemble natural bait, or if the movements of a badly impaled 

 worm are abnormal, or if the effluvia from the hand of the fisherman 

 has imparted an unusual scent to the bait — then the irritation is unfit 

 to produce the expected reflex. Again, the response depends upon 

 the characteristics of different species of fishes. There are some that 

 approach their food slowly and cautiously; others throw themselves 

 upon it headlong. The inert carp-like fishes and the vivacious sal- 



