viii RESPIRATION 



The mechanistic theory of life is now outworn and must soon 

 take its place in history as a passing phase in the development^ of 

 biology. But physiology will not go back to the vitalism which 

 was threatening to strangle it, and from which it escaped last 

 century. The real lesson of the movement of that time will never 

 be lost. 



The book belongs to a transition period, but the transition is 

 forward and not backward. My treatment of the subject may 

 possibly be looked on askance in some quarters as reactionary: 

 for I have been largely influenced by the ideas and work of older 

 physiologists. If, however, I have gone backward, it is only to 

 pick up clues which had been temporarily lost; and all of these 

 clues lead forward forward to a new physiology which embodies 

 what was really implicit in the old. 



The leaders of the mechanistic movement of last century got 

 rid of vitalism, but in doing so got rid of life itself. I have tried 

 to paint a picture of the body as alive. Though the picture is 

 imperfect, others will soon paint it more completely. The time 

 has come for a far more clear realization of what life implies. 

 The bondage of biology to the physical sciences has lasted more 

 than half a century. It is now time for biology to take her rightful 

 place as an exact independent science : to speak her own language, 

 and not that of other sciences. 



The endeavor to represent the facts of physiology as if they 

 would fit into the general scheme of a mechanistic biology has 

 led, it seems to me, to the present estrangement between physiology 

 and medicine. Since the time of Hippocrates the growth of 

 scientific medicine has in reality been based on the study of the 

 manner in which what he called the "nature" ( <iW ) of the 

 living body expresses itself in response to changes in environ- 

 ment, and reasserts itself in face of disturbance and injury. The 

 underlying assumption is that organic regulation and maintenance 

 represent something very real, and that only through the study 

 of it can we recognize and interpret disturbance of health, and 

 effectively aid maintenance or restoration of health. I have en- 

 deavored to return to what seems to me the truly scientific Greek 

 tradition, and to give it a form which is not only consistent with 

 modern science and philosophy, but brings physiology and medi- 

 cine into that close and special relation indicated by the common 

 etymology of the words "physician" and "physiology." 



Most of the investigations specially referred to in the book 

 have been carried out on man. It was only by human experiments 



