vi PBEFACE 



body seemed beyond their grasp. They had no diffi- 

 culty in understanding that the ameba gets oxygen be- 

 cause a gas passes in a definite direction, for the ameba 

 was unfamiliar and a new idea could be easily and 

 quickly gained concerning it; but almost simultane- 

 ously they would assert that a human being gets oxygen, 

 even in a vitiated atmosphere, because his system needs 

 oxygen. Their minds stopped working logically as 

 soon as human physiology, the familiar thing, was in 

 question. 



Until the simple fact that natural laws act upon all 

 organisms alike is grasped there can be no intelligent 

 comprehension of physiology and no intelligent applica- 

 tion of its laws to the health of the body. This fact is 

 the keynote of its rational presentation, and it should 

 be emphasized from the beginning, for if a correct gen- 

 eral impression is established, it may serve as a basis 

 upon which it is possible to build without first tearing 

 down and re-establishing the foundation. 



The course suggested in this book can be covered by 

 the work of a year. It divides itself naturally into two 

 parts. In the first part certain general principles are 

 defined and are shown to govern the functions of organ- 

 isms. In the second part modifications of these func- 

 tions resulting from structural development are con- 

 sidered in representatives of the great groups of 

 animals. 



It frequently happens that a teacher must make her 

 pupils conversant with a certain phase of a subject when 

 she knows that it will be better for them to have some 

 other phase of it emphasized. By following some such 



