viii PREFACE TO THE SECOND EDITION 



has an anaerobic start," anaerobic respiration should be taught 

 first; but there is an old rule of pedagogy which states that it is 

 better to proceed "from the known to the unknown" than in the 

 opposite direction. This has been found to hold true in both the 

 college and the kindergarten and there seems no excellent reason 

 to depart now from this accepted principle. 



The writer again has to thank his colleagues for their kindness 

 in pointing out errors in the previous edition, in making sugges- 

 tions for the book's improvement, and (last but by no means 

 least) in showing their appreciation by using it in their classes. 

 Special thanks must be given to the men who obligingly acceded 

 to the request for their photographs, and to Dr. H. S. Conard for 

 reading the proof and for his many helpful offices. 



Or an Raber 

 Biological Abstracts, Branch Office, 

 U.S.D.A., Washington, D. C, 

 April, 1933. 



