iv ELEMENTARY BIOLOGY 



the vastness of the living world, and the multiplicity of its interrela- 

 tions, without discouraging the aspiration to become acquainted with it 

 I have selected types of problems that best illustrate man's method of 

 adapting himself or his surroundings to his needs, and by means of 

 historical references I have sought to develop a recognition of the 

 interdependence of workers of all nations both in thought and in pro- 

 ductive labor, as well as our dependence upon the accumulations of the 

 past. Finally, the idea of progressive change in the organic world is 

 not only explicitly discussed in a special section, but is indirectly 

 suggested in the discussion of various processes and relations. 



As to quantity, I have assumed that there must be more material 

 in a textbook than can be comfortably used by any class of students. 

 This is in order to give the teacher an opportunity to select according 

 to individual preferences, according to local and temporary conditions, 

 and according to the interests of the" students ; and in order to give 

 individual pupils an opportunity to find things of interest that are not 

 " in the lesson." While the work of a class can never be completed 

 in any sense, it is desirable that the text give some suggestion of 

 scope, and that it project the imagination beyond what is actually 

 studied. Moreover, the more thoughtful student should have before 

 him, in connection with the topics discussed, supplementary matter 

 that will point out relations and applications in other fields of interest. 



As to method, I have assumed the correlation of textbook with lab- 

 oratory work, with field excursions, with special topic assignments, and 

 with the study of museum material. But while constantly referring to 

 experiments and to objective data, the text is not interrupted with lab- 

 oratory directions. I have sought here not merely to keep the reading 

 continuous ; I have meant to indicate that there is no one best experi- 

 ment, no one set of facts, no one type specimen, to support a principle. 

 Truth may be approached by many paths, and I have tried to avoid 

 dogma both as to the approach and as to the conclusions. The relation 

 of science to human welfare is illustrated by the introduction of an 

 unusual amount of quantitative material, chiefly in the form of graphs. 

 This is on the theory that it is not sufficient to show that a scientific 

 principle is reasonable or helpful ; it is necessary to show that there 

 is a measurable difference in results when various principles are applied. 

 There is no better way of insinuating into the thought of our 

 students the j*eal meaning of the pragmatic sanction. 



