viii PREFACE 



experiment as is the case with such sciences as 

 chemistry and physics. This book is accordingly 

 planned to supply a background for a laboratory 

 course in Biology and to supplement the facts ac- 

 quired in such a course, the exact nature of which 

 will depend upon the convictions or preliminary 

 training of the individual instructor. 



On the other hand, it is believed that the general 

 reader also will find here a simple statement of the 

 fundamentals of General Biology, a subject that is 

 becoming increasingly important in our everyday life. 



In covering so much ground I have been compelled 

 to condense many subjects to paragraphs that might 

 well have deserved whole chapters to themselves. 

 The wide-awake teacher, I think, will have no diffi- 

 culty in amplifying those portions that he esteems 

 most important or in which he is most interested. 

 I am conscious, too, of the fact that many generali- 

 zations have been stated in a much less cautious 

 way than would have been the case if condensation 

 had not seemed so essential a feature. But, apart 

 from this, I think that it is preferable, pedagogically, 

 that a student should get a few clean-cut funda- 

 mental ideas which perhaps require subsequent qual- 

 ification than that he should have vague notions in 

 which exceptions to rules figure as largely as the 

 rules themselves. For instance, it is best that he 

 should acquire the fact that the division of chromo- 

 somes in mitosis is equal and that in consequence 

 the number of chromosomes in an individual or a 

 species is constant, leaving any consideration of the 



