10- EQUILIBRIUM OF LIFE. 



in civilized and savage countries, submit to a hard destiny. To obtain 

 their daily bread is the great object of life. 



What is the philosophical explanation of this necessity for a supply 

 of air, of water, of food ? Why is it that the system will bear so little 

 delay ? 



The answer which Physiology gives to these questions is an answer 

 Life de ends ^ ommous import, but the whole science is a commentary on 

 on destruction its truth. The condition of life is death. No part of a liv- 

 of material. ^ mecnan i sm can ac t without wearing away, and for the 

 continuance of its functions there is therefore an absolute necessity for 

 repair. 



It has been greatly to the detriment of physiology and the practice of 

 medicine that this conception has not been thoroughly realized until late 

 times. The aspect of identity which an animal presents is an illusion, 

 hiding from us the true state of the case. It has been the fruitful source 

 of errors which have retarded the progress of these sciences. What could 

 their career possibly be when men had persuaded themselves that a liv- 

 ing being possesses a capacity for resisting any change, and that organic 

 structures never yield to external physical influences until after death ? 



But life, far from being a condition of immobility, is a condition of 

 ceaseless change. An organism, no matter of what grade it may be, is 

 only a temporary form, which myriads of particles, passing through a de- 

 terminate career, give rise to. It is like the flame of a lamp, which pre- 

 sents for a long time the same aspect, being ceaselessly fed as it ceaselessly 

 wastes away. But we never permit ourselves to be deceived by the sim- 

 ulated unchangeableness which such a natural appearance offers. We 

 recognize it as only a form arising from the course which the disappear- 

 ing particles take. And so it is even with man. He is fed with more 

 than a ton weight of material in a year, and in the same time wastes more 

 than a ton away. 



There is, therefore, a general condition of equilibrium which every an- 

 Conditions of * ma ^ P resem X depending upon its receipts and its wastes, a 

 equilibrium in proper knowledge of the conditions of which is at the founda- 

 tion of Physiology. That we may approach this problem un- 

 der its simplest form, free it from all unnecessary complications, and make 

 it of most interest to the special object of this book, the remarks now 

 to be made will be confined to our own species, and, except when oth- 

 erwise stated, to a condition of health, and to the adult period of life. 



To have a uniform standard of reference, we may assume one hundred 

 and forty pounds as the weight of an adult healthy man. Now the con- 

 stant consumption of food, water, and atmospheric air tends steadily to 

 increase that weight, and even in a very short time a disturbance arising 

 from these sources would be perceptible, w^ere there not some causes of 



