1 68 COMPARATIVE PHYSIOLOGY 



represented by a fraction of a tone. Similarly a fine degree of 

 discrimination of time, doubtless connected with the mechanism 

 of inhibition by retardation mentioned above, is shown by 

 the fact that differential response to a metronome beating 104 

 and 100 per minute can be established and maintained for 

 periods of over twenty-four hours. The application of this 

 method of analysis shows, on the other hand, that dogs and cats 

 are completely colour-bUnd, their world being defined usually 

 by differences of light- intensity like an ordinary photograph. 



Further Reading 



Herter. Mechanische Sinnesorgane U. S. W. Leipzig. 

 LoEB. Forced Movements, Tropisms and Animal Conduct. Lippincott. 

 Parker. The Elementary Nervous System. Lippincott. 

 Sherrington. The Integrative Action of the Nervous System. Yale 

 University Press. 



