INTRODUCTION. 1 1 



most of its phases can be studied well in the winter, leaving 

 the spring for the study of growth and irritability, which need 

 the brighter and warmer season. Topics which cannot be 

 practically studied, but are nevertheless important, are intro- 

 duced in their proper places in order to keep correct propor- 

 tion, as already explained; paragraphs and connecting 

 sentences are introduced here and there to show the relation 

 and connection of topics and to help to bind the whole into 

 one symmetrical system. It may seem at times that too great 

 stress is laid upon comparatively unimportant topics, but for 

 this there is always a reason. Thus, a good deal of attention 

 is given to the responses of protoplasmic movement to varia- 

 tions of temperature, although that subject is in itself not nearly 

 so important as many others more briefly treated. The reason 

 for the apparent emphasis is that this particular topic, coming 

 very early in the course, affords a remarkably good opportunity 

 to introduce students to exact quantitative methods, and their 

 expression by tabulation and construction of curves ; and to the 

 methods of elimination of individual errors. The theory of 

 every experiment is given and the reason for each step; and, 

 for completeness, references are added to other ways of attack- 

 ing the same or related problems. Here and there synoptical 

 essays are called for, on the scope and value of which some 

 comments will be found in the next chapter. Supplementary 

 or correlated topics, not belonging in the main framework of 

 the course, are mentioned at the ends of the sections with 

 which they are connected ; these topics may well be discussed 

 by the teacher in the lectures. All of the topics, for reasons 

 already given, i.e., to bring them into the form of investiga- 

 tions, are presented as problems introduced by questions. The 

 form of these questions, and their number and sequence, are 

 of great importance, and have been given much study. 

 Through them the students' energy may be concentrated, their 

 attention directed in the most profitable lines, and their mode 

 of attack on the problems made inductive; while through them, 

 too, much both of stimulus and suggestion may be conveyed. 



