PREFACE xvii 



pleads for a more general use of small mammals as laboratory 

 materials in a general course. 



It is a common experience that most of the students in courses in 

 General Biology have had no previous training in Chemistry, or at 

 most a preparatory school course in that science. The present status 

 and outlook of the science of Biology demands that one must have 

 at his command at least the rudiments of the science of Chemistry 

 in order to appreciate the principles as they are weighted; vital 

 phenomena are evidences of the dynamics of matter. The responsi- 

 bility for establishing a background of knowledge of the structure 

 and behavior of matter devolves upon the instructor in Biology; 

 without it he cannot successfully develop his subject. More especially 

 is his responsibility real because in very many cases Biology is the 

 only science scheduled in the curricula of particular students. An 

 attempt is made here to develop just so much of the principles of 

 Chemistry that at the very start the student is indoctrinated with 

 the concept of Mechanism and establishes as a point of departure the 

 First Principle, that life is dynamic. The writer appreciates the 

 difficulties involved and recognizes the fact that a comprehension 

 of even the rudiments of the structure and behavior of matter re- 

 quires that the student exercise a controlled and vivid imagination 

 and that he be able to project his imagination into the realm of the 

 infinitely small, properties of mind that are usually associated with 

 maturity and with the experience gained by slow development of 

 logical thinking. The difficulties faced do not justify one in avoiding 

 the attempt; it has been gratifying to realize that a certain degree of 

 success is attained with some frequency. 



The writer is well aware of the fact that the text contains some 

 repetitions. For instance, the hydra is described no less than three 

 times in different sections of the volume. Experience has taught that 

 for pedagogical reasons this is quite desirable. It will be noted that 

 in each case of apparent repetition the subject matter is developed 

 from a different point of view; under such circumstances re- 



