PHYSIOLOGY OF THE CIRCULATION. 69 



and as that power of contraction is more marked in 

 the distal part of the arterial twigs than at their 

 point of origin from the main branch, it should 

 follow that each minute stream of arterial blood will, 

 if there be any difference in this respect, rather flow 

 from the wider to the narrow portion of the tube. 



Now the existence of these obstacles being un- 

 doubted, and their sum being so very considerable, 

 are we to regard them as defects in the constitution 



o 



of the circulation unavoidable perhaps, but never- 

 theless involving a certain loss of power which might 

 otherwise have been usefully employed in propelling 

 the blood ? And if the mere passage of that fluid 

 through its vessels be deemed the sole intelligible 

 part of the circulation, if we are to forbear from 

 inquiring in what manner it produces its known 

 beneficial effects upon the system, I do not see how 

 some such supposition is to be avoided. But since 

 it is possible that these very impediments to the 

 circulation may in reality be contrivances adapted 

 to the performance, by it, of some important func- 

 tions, we are, I think, required, were it but in 

 acknowledgment of the universal wisdom of nature's 

 plans, to pause before we pronounce these apparent 

 imperfections altogether inoperative, or disadvan- 

 tageous. It therefore remains for us to inquire 

 whether any peculiarity in the physical condition of 

 the arterial blood is induced by the existence of 

 these obstructing causes. And supposing this ques- 

 tion to be answered in the affirmative, it will still 

 remain to determine how far that physical condition 



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