PREFACE ix 



tion to the structure, physiology, and economic benefit of 

 these organisms. But since so much may be done to prevent 

 disease, we have also considered with some degree of thor- 

 oughness the disease-producing effects of several of the 

 pathogenic forms. 



No study of human biology should be allowed to leave in 

 the mind of the student the idea that he is merely a chemical 

 engine adapted only for the generation of a certain amount 

 of physical energy. The primary object of all secondary 

 education should be the development of character and effi- 

 ciency, and the true teacher ought to find opportunity again 

 and again to touch the individual life of the young student. 

 Especially should this be true in the study of biology. 

 Growing boys and girls ought to come to feel, as they have 

 never felt, that they have in their keeping a most complex 

 and wonderful piece of living machinery which can be easily 

 put out of order or even wrecked. But, on the other hand, 

 they should see that if the bodily machine is well cared for, 

 it is capable of splendid work which may help to increase 

 the sum total of human efficiency and happiness. 



In the preparation of this volume the authors have re- 

 ceived a great many suggestions from the teachers in their 

 own departments and those in other schools. We have been 

 especially fortunate in securing the assistance of experts who 

 have read much of the manuscript and many of the proof 

 sheets. Dr. E. P. Felt, New York State Entomologist, Mr. 

 E. R. Root, author of " A. B. C. of Bee Culture," and 

 Professor Glenn W. Herrick of Cornell University, have given 

 us valuable criticism of the chapter on Insects. Dr. W. T. 

 Homaday, Director of the New York Zoological Park, has 

 read the chapters on Birds and Fishes. To Mr. J. M. John- 

 son, Head o^ Department of Biology of the Bushwick High 

 School, we are also indebted for suggestions relating to Birds. 



