j v PREFACE 



paragraphs at the beginning of many of the chapters and 

 the summaries throughout the book, as well as the general 

 arrangement of the subject-matter, will be found helpful. 



Since the custom largely prevails of teaching physiology 

 in advance of the sciences upon which it rests biology, 

 physics, and chemistry care should be exercised to de- 

 velop correct ideas of the principles and processes derived 

 from these sciences. Too much latitude has been taken 

 in the past in the use of comparisons and illustrations drawn 

 from " everyday life." To teach that the body is a " house," 

 " machine," or " city " ; that the nerves carry " messages " ; 

 that the purpose of oxygen is to "burn up waste"; that 

 breathing is to " purify the blood," etc., may give the pupil 

 phrases which he can readily repeat, but teaching of this 

 kind does not give him correct ideas of his body. 



The method of teaching, however, that uses the pupil's 

 experience as a basis upon which to build has a value not 

 to be overlooked. The fact that such expressions as those 

 quoted above are so easily remembered proves the value 

 of connecting new knowledge with the pupil's experience. 

 But the inadequacy of this experience must be recognized 

 and taken into account. The concepts of the average 

 pupil are entirely too indefinite and limited to supply the 

 necessary foundation for a science such as physiology. 

 Herein lies the great value of experiments and observa- 

 tions. They supplement the pupil's experience, and in- 

 crease both the number and definiteness of his concepts. 

 No degree of success can be attained if this phase of the 

 study is omitted. 



The best results in physiology teaching are of course 

 attained where laboratory work is carried on by the pupils, 

 but where this cannot be arranged, class experiments and 

 observations must suffice. The Practical Work described 



