\i PREFACE TO THE SECOND EDITION. 



these facts can be conveyed by tlie metliod of study liere out- 

 lined ; but we must emphatically insist that neither this nor any 

 Xother method will give good results unless rightly used, and that 

 C this work is not designed to be a complete text-book. Probably 

 few teachers will find it desirable to go over the whole of the 

 ground here laid out, and we hope that still fewer will be inclined 

 to confine their work strictly to it. Even in a brief course the 

 student may, after going over certain portions of this work, be 

 made acquainted with the leading types of plants and animals ; 

 and this may be rapidly accomplished if the introductory work, 

 however limited, has been carefully done. In extended courses 

 we have sometimes found it desirable to postpone certain parts of 

 the introductory work, returning to them at a later period. 



A second modification consists in placing the study of the 

 animal before that of the plant, which plan on the whole appears 

 desirable, especially for students who have not been well trained 

 in other branches of science. The main reason for this lies in the 

 greater ease with which the physiology of the animal can be ap- 

 proached ; for there is no doubt that beginners find the nutritive 

 problems of the plant abstruse and difiicult to grasp until a cer- 

 tain familiarity with vital phenomena has been attained ; while 

 most of the physiological activities of the animal can be readily 

 illustrated by well-known operations of the human body. 



The third change is the omission of the laboratory directions, 

 these" havih^~beentound "TmsuitabTe! The needs~of different 

 teachers differ so widely that it is impossible to draw up a scheme 

 that shall answer for all. In place of the laboratory directio ns for 

 students we have therefore given, in an appendix, a series (fTprac- 

 ticaFsucrffestions to teachers, leaving^ it to them to work OTxde- 

 taHed directions, if desirecT/ by the help of the standard labora- 

 tory manuals. These suggestions are the result of a good deal of 

 experience on the part of many teachers besides ourselves, and 

 we hope they will be found useful in procuring and preparing 

 material (often a matter of considerable difficulty), and in decid- 

 ing just what the student may reasonably be expected to do. 



For the rest, the original matter has been thoroughly re^dsed, 

 numerous errors have been corrected, and many additions made, 

 particularly on the physiological side. 



September, 1895. 



