PREFACE 



Then there arose still another group of inquiring minds. 

 Members of this school could not see anything worth while 

 in knowing merely either what an animal did or how it was 

 made. They devoted their efforts to discovering the 

 secrets of its workings. They invented instruments for 

 measuring the power of its muscles, for testing the nature 

 of the force that resides in its nerves; they made analyses 

 of its food and its tissues; they devised all kinds of experi- 

 ments for revealing the causes of its behavior. The work- 

 ers in this branch, the physiologists, had to have a con- 

 siderable grounding in physics and chemistry; conse- 

 quently they came to write more or less in the languages 

 of those sciences and to express themselves in chemical and 

 mathematical formulae. Their writings are hard for the 

 public to understand. Their statements, moreover, are 

 often at odds with preconceived "ideas, since precon- 

 ceived ideas are conceived in ignorance, and the public at 

 large does not take to this sort of thing — it cherishes above 

 all its inherited opinions. 



Therefore the old-time naturalist is still venerated, as 

 he deserves to be, and those who call themselves "nature 

 lovers" still like to decry the laboratory worker as an evil 

 being who would take the beauty from nature and destroy 

 the soul of man. A modern writer of the old school may 

 sell his wares, but when something goes wrong with his 

 stomach or his nerves, or when his plants or his animals 

 are attacked by disease, it is the knowledge of the labora- 

 tory scientist that comes to his aid. 



The reason that the specific truths of nature must be 

 found out in laboratories is that there are too many things 

 mixed together in the fields. The laboratory naturalist 

 endeavors to untangle the confusion of elements in the 

 outdoor environment and to isolate the different factors 

 that affect the life and behavior of an animal, in order 

 that he may be sure with just what he is dealing in his ef- 

 forts to determine the value of each one separately. By 

 creating a set of artificial environments in each of which 



