N recent years many biologists have come to believe that most 

 of the behavior of the simplest animals and some of the actions 

 of the higher are controlled in a much more rigidly mechan- 

 ical way than has usually been admitted; that, in a word, much 

 of the action, and apparent instinctive or intelligent response of animals to 

 external conditions, is an immediate physico-chemical rather than an inex- 

 plicable vital phenomenon ; that the animal body in its relation to the external 

 world is much more like a passive, senseless, although very complex, machine, 

 stimulated and controlled by external factors and conditions, than like the per- 

 cipient, determining, purposeful creature that our usual conception of the 

 organism makes it out to be. 



Clever experimenters, as Loeb, Lucas, Radl, Bethe, Uexkull, and numer- 

 ous others, believe themselves justified in explaining a host of the simpler 

 actions or modes of behavior of animals on a thoroughly mechanical basis, 

 as rigorous, inevitable reactions to the influence or stimulus of light, heat, 

 contact, gravity, galvanism, etc. Phototropism, stereotropism, geotropism, 

 etc., are the names given to these phenomena f response by action and 

 behavior to stimuli of light, contact, gravity, etc., respectively. 



Some of these biologists are ready to carry their giving up 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 continually 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 super- 

 natural powers of the theologians, which are also said to determine motions, 

 but upon which an engineer could not well rely. 



635 



