Chapter I 



INTRODUCTION 



<§. 1. A living organism is much the same day after day, not only 

 in form but in function. If I count my heart beats for a minute 

 each morning before getting out of bed, I find the frequency of 

 beats only less constant than the length of my foot. The foot looks 

 like a permanent mold in which matter is cast. Actually it swells 

 and shrinks with each pulse of blood coming to it, each change of 

 posture, and each meal. Its substance changes from month to 

 month. The beats of the heart appear to be accurately meted out 

 without a visible pendulum. During a day many an acceleration 

 of frequency occurs ; but when rest or other uniform state of body 

 prevails, the frequency quickly returns to its characteristic value. 

 That constancy represents a physiological regulation. 



Every biologist, indeed every owner of a pet, expects his animal 

 to be nearly the same every day ; to show the same movements, the 

 same responses to signals, the same posture, and the same food con- 

 sumption. If not, he decides there is ' ' something wrong. ' ' The 

 certainty that he feels about the animal's health is similar to that 

 which he feels about the performance of his automobile, his kitchen, 

 or his piano. He has come, by experience, to expect uniformities 

 of particular sorts. Failure of the car's motor to start is for him 

 as uncommon as failure of the car's fender to keep its shape. 

 Accumulated experiences seem to make a man more and more 

 confident of always finding particular features that he can count 

 on in his machine or instrument. 



In much the same way, the biologist becomes intimate with the 

 uniform characteristics of each animal dealt with, and the phy- 

 sician notices small departures from regularity in his old patient. 

 All this is a tribute to constancy of physiological function, a recog- 

 nition that each living individual tends in many ways to be like 

 itself at each observation. 



Regulations mean, then, in physiological science, those self- 

 managements of organisms which result in constancy of function. 

 TV^at do animals do to maintain their physiological constitutions 

 and activities ? Functional arrangements evidently work hand-in- 

 hand with structural, chemical, and other kinds of arrangements ; 



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