INTRODUCTION. 



GENERAL VIEW OF THE CONNECTION OF PHYSIOLOGY WITH OTHER BRANCHES 



OF MEDICINE. 



1. THE object of the Science of Physiology is to bring- together, in a sys- 

 tematic form, the phenomena which normally present themselves during the 

 existence of living beings ; and to classify and compare these, in such a man- 

 ner as to deduce from them the general laws or principles, by which they are 

 regulated. In order to attain a correct knowledge of the latter, a very exten- 

 sive comparison is requisite. Principles, which might seem of paramount 

 importance in regard to one group of living beings, are often found, on a more 

 general review, to be quite subordinate. For example, the predominance of 

 the Nervous System in the higher classes of Animals, and its evidently close 

 connection with many of the functions of life, have led several physiologists to 

 the opinion, that its influence is essential to the performance of the functions 

 of Nutrition, Secretion, &c. : but, on turning our attention to the Vegetable 

 kingdom, in which nothing analogous to a nervous system can be proved to 

 exist, we find these functions going on with even greater activity than in 

 Animals. It is clear, therefore, that they may be performed without it ; and 

 on a closer examination of the phenomena presented by Animals, it is seen 

 that they may be explained equally well, or even better, on the principle that 

 the nervous system has a powerful influence on these actions, than on the idea 

 that it affords a condition essential to them. This is only one out of many 

 instances 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 erect any general principles in 

 Physiology. 



2. The object of the present work, 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 what may be called his normal life. Every one 

 knows the difficulty of defining the two conditions health and disease. The 

 former may be said to be that state in which the various actions of life are 

 normally or regularly performed ; and the latter to result from a disturbance 

 or irregularity in these actions, constituting an abnormal state. But this is 

 only substituting one term for another ; the difficulty remains the same. 

 Many variations occur, within the limits of what must be called in some per- 

 sons the normal state, which in others must be regarded as abnormal actions. 

 Thus in most adults the pulse averages about 70;. but it is easily raised by 

 exercise to 90, without any injurious consequences ; and such must be regarded 

 as a normal or physiological state. But we occasionally meet with instances 

 in which the usual pulse is not quicker than 40 ; and for this to rise to 90 

 might indicate a very alarming state of the system ; since there are individuals 



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