vi EDITOR'S PREFACE. 



position of the fluids and membranes, have a more 

 direct, constant, and essential influence on the mo- 

 tion of the animal fluids, and, consequently, on the 

 state of the health, than has been usually supposed, 

 it is evident that very much remains to be done in 

 tracing that influence under the ever varying cir- 

 cumstances of the animal body, and in applying the 

 knowledge thus acquired to the purposes of hygiene 

 and therapeutics. But it is equally obvious, that 

 the above-mentioned mechanical and chemical 

 causes are not alone sufficient to explain the phe- 

 nomena of animal life, since they are present equally 

 in a dead and in a living body ; so that while every 

 advance in physiology enables us to explain more 

 facts on chemical and mechanical principles, some- 

 thing always remains, which, for the present, is 

 beyond our reach, and which may for ever remain 

 so. However this may be, the facts established in 

 this and in the preceding work of the Author have 

 very materially extended the application of the well- 

 known laws of physics and of chemistry to phy- 

 siology, and have also furnished a number of the 

 most beautiful instances of that infinitely wise, but 

 exquisitely simple adaptation of means to ends, 

 which characterizes all the works of the omnipotent 

 Creator ; but which is nowhere more admirably dis- 



