iv PREFACE 



While fully realizing and urging the value of experi- 

 mental work, I have, nevertheless, so planned the text 

 that it is independent of the experiments in connection 

 with each chapter. Those schools, therefore, which lack 

 either the time or the equipment for such work, will not 

 find the book less well fitted for their use. By them, the 

 book can be completed in half a year. For those who can 

 carry out the laboratory work, the book offers either a 

 half or a full year's course, depending upon whether 

 the experiments are demonstrated by the teacher or done 

 by the students. 



The experiments and demonstrations should be so 

 planned that, when necessary, the one-hour period may 

 be extended to two hours. In nearly all cases, the experi- 

 ments should precede the text, that the student may be 

 led, in so far as is possible, to make his own observations 

 and conclusions. In order to get the most value from 

 the work, a systematic record of the experiments should 

 be kept in a notebook, to be regularly examined by the 

 teacher. 



Aside from those herewith acknowledged, many of the 

 illustrations are new, being either original or redrawn 

 from the best sources obtainable. To Dr. O. P. Bellin- 

 ger of Clark University I am indebted for permission to 

 copy his remarkable photographs of the ameba. I am 

 further indebted to the following authors and publishers 

 for permission to use certain cuts from their works: 

 Tigerstedt's Physiology, Mill's Comparative Physiology, 

 Doty's Prompt Aid to the Injured, (D. Appleton and 

 Co.) ; Bergen and Davis' Principles of Botany, Conn's 

 Bacteria, Yeasts and Molds in the Home, Hough and 

 "Sedgwick's The Human Mechanism, (Ginn and Co.) ; 

 Oerrish's Anatomy, Hall's Physiology, Egbert's Hy- 

 giene, (L<ea Bros, and Co.) ; Martin's Human Body, 



