38 INTRODUCTION. 



presented by Animals, it is seen that these may be explained better, on the 

 principle that the nervous system has a powerful influence on such actions, 

 than on the idea that it affords a condition essential to them. Recent inquiries 

 have shown that the agents immediately concerned in these operations are of 

 the same nature in both kingdoms ; the separation of the nutrient materials 

 from the circulating fluids, or the elimination of substances which are to be 

 withdrawn from it, being performed in the animal, as in the plant, by cells, in 

 the manner to be explained hereafter. This is only one out of many in- 

 stances, which it would be easy to adduce, in proof of the necessity of bring- 

 ing together all the phenomena of the same kind, in whatever class of living 

 beings they may be presented, before we attempt to erect any general princi- 

 ples in Physiology. 



The object of the present treatise, however, is not to follow out such an 

 investigation ; but to show the detailed application of the principles of which 

 Physiological science may now be said to consist, to the phenomena exhibited 

 by the Human being during the continuance of health or normal life. These 

 phenomena, when they occur in a disturbed or irregular manner, constitute 

 disease or abnormal life ; and become the subjects of the science of Pathology. 

 It is impossible to draw a precise line of demarcation, between the states of 

 health and disease ; since many variations may occur, which do not pass the 

 limits of what must be called in some individuals the normal state, but which 

 must be regarded as decidedly abnormal actions in others. The sciences of 

 Physiology and Pathology, therefore, are very closely related to each other; 

 and neither can be pursued with the highest prospect of success, except in 

 connection with the other. 



Equally close is the relation between Hygiene, or the art of preserving 

 the body in health, which is founded on the science of Physiology, and 

 Therapeutics, which is the art of curing disease, founded upon the science of 

 Pathology. In proportion as the science of Physiology is perfected, will the 

 simplicity and certainty of its practical applications increase ; and although 

 we may not anticipate a return of patriarchal longevity, yet the experience of 

 the last century has amply shown, that every general increase of attention to 

 its simple and universally-acknowledged truths is attended with a prolonga- 

 tion of life, and contributes to that not less important object, its emancipation 

 from disease. In like manner, with every advance in Pathological science, 

 will the art of Therapeutics lose its merely empirical character, and become 

 more and more rational ; that is, the rules laid down for the treatment of 

 disease will be less and less founded upon the results of a limited experience 

 as to the efficacy of particular remedies in removing certain abnormal phe- 

 nomena ; and will have reference more and more to the nature of the morbid 

 action, which is indicated by the symptoms. Thus, when the urine presents 

 a particular sediment, our inquiries are directed, not so much to the condition 

 of the kidney itself, as to the constitutional state which causes an undue 

 amount of the substance in question to be carried off by the urinary excre- 

 tion, or which prevents it from being (as usual) dissolved in the fluid. 



In proportion as our treatment of disease thus loses its empirical character, 

 and is founded on scientific principles, must it increase in perfection and suc- 

 cess ; and in like proportion will the Medical Profession acquire that dignity 

 to which the nobility of its objects entitles it, and that general estimation 

 which will result from the enliglitened pursuit of them. 



