TEACHING AND LEARNING 23 



In a course such as this, which brings the student so often 

 to the borders of philosophy, some attention must be given to 

 theories and theorizing, and even to speculation. Theorizing 

 has this justification, that the current theories which explain 

 important phenomena have much value as knowledge to per- 

 sons of culture, and they give a life and significance to facts 

 otherwise of little meaning. They stimulate interest and mental 

 activity, and are actually an invaluable tool of scientific research. 

 But no student is prepared to understand the place and bearing 

 of the leading theories unless he has, first, made personal acquain- 

 tance with the facts they are designed to explain, and, second, 

 has tried to develop for himself some interpretation of those 

 facts. Students receive with but a languid interest such theories 

 as that of the micellar basis of membranes, or those which 

 explain osmotic pressure, when these are formally presented to 

 them; but they receive these theories with a very different 

 interest when offered after they have tried themselves to devise 

 an explanation of the facts they have observed in their studies 

 upon those matters. All such theorizing, however, must be 

 kept in rigid control, subordinated to facts, a means to an end, 

 never an end in itself. The tentative and insufficient nature 

 of even the most widely accepted theories should be illustrated 

 by subjecting them to rigid criticism. It must be made clear 

 that theories are mostly attempts to explain in a subjective form 

 phenomena which may not be subjectively comprehensible at all. 



Turning now to actual procedure in the conduct of the course, 

 I think of but little to add. The individual work of the student 

 in the laboratory, under the criticism and suggestion of the 

 teacher, is its most important part, but this should be supple- 

 mented by the approved devices of lectures,* conferences, semi- 



* For illustration of lectures, etc., wall diagrams have their value. Two sets 

 have been published for physiological use — an earlier, 60 in number, each 69X85 

 cm., by Frank and Tschirch (published by Paul Paeey, Berlin, and costing 

 180 marks), and a. later, 15 in number and somewhat larger, by Errera and 

 Laurent (published by H. Lamertin, Brussels, and costing 50 francs). They 

 may be imported through any dealer in foreign books. 



On the projection of various physiological processes upon a screen, for demon- 



