INTRODUCTION 11 



supposedly conscious an action as recognizing a tasty 

 food can, in a short time, become nothing but a mere 

 mechanical and associative action. 



"Yes," you may say, "we can understand all that, but 

 why experiment on individual cells, and on one-celled 

 animals; what good to humanity can one hope to find 

 there?" 



I think the most satisfactory way to acquaint the non- 

 biological listener with the underlying reasons for experi- 

 mental work on such individual cells of the body and on 

 one-celled organisms, is to show how such work changes 

 our whole conception of the treatment of disease in both 

 the physical and the mental realms. I quote the words of 

 Dr. Stephen Smith, an eminent psychiatrist of the genera- 

 tion just passed. He says : 



"The lessons which the illustrations of the anatomy 

 and physiology of the nervous system teach, have a wide 

 application to our treatment of the dependent classes. We 

 learn that the mental attributes of every person depend 

 ultimately upon the physical state of the cell, over which 

 we have almost absolute control in its individual and col- 

 lective capacity. If its texture is feeble from heredity or 

 disease, we may make it strong by nutrition, exercise, 

 pure air, and medication; if it is undeveloped, we can 

 develop it by applying appropriate stimulus and suitable 

 nourishment; if it is unduly developed and overactive, 

 we can reduce it to a rudimentary and inactive state by 

 removing every form of stimulant and reducing its nutri- 



