

Chapter XXI, 



THE CIRCULATION. 



THE phenomenon of the circulation is of so interesting and re- 

 markable a character, and its condition has such an influence 

 upon the health, that I think it advisable, as an introduction to 

 the Medical Department, to make some reference- to it. There are 

 so many diseases and difficulties of a serious character which are the 

 result of derangements of circulation, that it certainly seems neces- 

 sary to give, some explanation of it, that the reader may be im- 

 pressed the better with the necessity for such prudence and care as 

 would prevent its disturbance.. The writer thinks it also advisable, 

 instead of giving a labored description, which may be easily ob- 

 tained from any physiology, and which but few would take the 

 trouble to read, to do this mainly by the aid of illustrations, a va- 

 riety of which have been included at considerable expense. 



General Plan of the Circulation. 



The blood is circulated through the body for the purpose of nu- 

 trition and secretion, by means of one forcing-pump ; and through 

 the lungs, for its proper aeration, by another ; the two being United 

 to form the heart. This organ is therefore a compound machine, 

 though the two pumps are joined together, so as to appear to the 

 casual observer to be one single organ. In common language, the 

 heart of the mammalia is said to have two sides, each of which is a . 

 forcing-pump ; but the blood, before it passes from one side to the 

 other, has to circulate through one or the other set of vessels found 

 in the general organs of the body or in the lungs, as the case may 

 be. This is shown at Fig. 692, where the blood, commencing 

 with the capillaries on the general surface, passes through the 

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