INTRODUCTION 35 



our public more appreciation of conditions necessary for a fish to 

 live. A fish needs suitable water conditions including proper gas 

 content, salt balance, nesting places, vegetation, and freedom from 

 chemical or oil pollution. 



The strictly intellectual and cultural endowments which zoology 

 has given man are no less valuable than the tangible gifts. To 

 understand something of the orderly conduct of Nature and to see 

 that her operations are in accord with definite principles, gives one 

 insight to the solution of many of the problems of life. Many of 

 the superstitious dreads of unseen monsters have been eliminated 

 by the knowledge of the fundamental principles of life processes. 

 In recent times, it is probably true that nothing has influenced the 

 thinking of the world more than the ideas, principles, and knowl- 

 edge growing out of biological study. 



