REFLEXES, INSTINCT, AND REASON 429 



of other than mechanical behavior among animals to great 

 lengths. Loeb introduces a paper written in 1890 on instinct 

 and will in animals as follows: 



'In the biological literature one still finds authors who treat the 

 ' instinct ' or the ' will ' of animals as a circumstance which determines 

 motions, so that the scientist who enters the region of animated nature 

 encounters an entirely new category of causes, such as are said contin- 

 ually to produce before our eyes great effects, without it being possible 

 for an engineer ever to make use of these causes in the physical world. 

 ' Instinct' and ' will' in animals, as causes which determine movements, 

 stand upon the same plane as the supernatural powers of theologians, 

 which are also said to determine motions, but upon which an engineer 

 could not well rely. 



"My investigations on the heliotropism of animals led me to 

 analyze in a few cases the conditions which determine the apparently 

 accidental direction of animal movements which, according to tradi- 

 tional notions, are called voluntary or instinctive. Wherever I have 

 thus far investigated the cause of such 'voluntary' or 'instinctive' 

 movements in animals, I have without exception discovered such 

 circumstances at work as are known in inanimate nature as determi- 

 nate movements. 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." 



But Jennings, a very careful and industrious student of the 

 behavior of the protozoa, whose studies have been perhaps more 

 detailed and prolonged than those of any other investigator of 

 the same subject, closes a fascinating volume on his work with 

 the following paragraph: 



"The present paper may be considered as the summing up of the 

 general results of several years' work by the author on the behavior of 

 the lowest organisms. This work has shown that in these creatures the 

 behavior is not as a rule on the tropism plan a set, forced method of 

 reacting to each particular agent but takes place in a much more 

 flexible, less directly machinelike way, by the method of trial and 

 error. This method involves many of the fundamental qualities 



