214 THE SCIENCE OF BIOLOGY 



Experimentation is the conspicuous method, through- 

 out this modern study of behavior. Observation is still 

 fundamental and is often the only feasible means of attack- 

 ing the problems. But here, as in other scientific lines, the 

 experiment under controlled conditions is the goal of inves- 

 tigation. In recent years the study of behavior has been 

 extended to the lower organisms, in the hope that simpler 

 forms of life would be more understandable in this particular 

 and that simpler types of behavior would be discovered and 

 synthesized to explain the reactions of higher animals. 

 Much has been accomplished. The behavior of forms like 

 the infusoria is now believed to be vastly simpler than when 

 likes and dislikes, comparable to those of men, were ascribed 

 to these lowly beings. Yet the reactions of the animal cell 

 are much the same, whether the cell is that of an amoeba or 

 one within the human body. The responses, which the living 

 protoplasm makes to changes in its environment, are more 

 complex in the many-celled body, in so far as this body con- 

 tains many different kinds of cells. But it is not clear that 

 the responses of individual cells of the many-celled body 

 are more complex than the responses of the individual cells 

 of the protozoa. The principal advance that has been made, 

 toward analysis and subsequent synthesis of the elements 

 of behavior, is the showing that behavior is, in its last analy- 

 sis, a problem of cellular functions. 



PROBLEMS OF NATURAL HISTORY 



We have seen that during the Scientific Renaissance 

 studies in natural history constituted one of the two great 

 lines of biological advance. Until the middle of the nine- 

 teenth century, perhaps the major part of zoological effort 

 was devoted to studies upon animals and plants in the open 

 country. The work to which the naturalist gave himself 

 within doors was carried on primarily with a view to the 

 classification of material collected in the field. 27 The an- 



27 Such work as that recorded in Darwin's " Naturalist's Voyage round 



