VESSELS OF ANIMALS. 113 



lire art' all against them. The blood, in its proper course, 

 has no tendency to produce such things ; and in its improper 

 or reflected current, has a tendenc)'^ .to prevent their produc- 

 tion. While we see, therefore, the use and necessity of this 

 machinery, we can look to no other account of its origin or 

 formation than the intending mind of a Creator. Nor can 

 we without admiration reflect, that such thin membranes, 

 such weak and tender instruments as these valves are, should 

 be able to hold out for seventy or eighty years. 



Here also we cannot consider but with gratitude, how 

 happy it is that our vital motions are involuntary. We 

 should have enough to do, if we had to keep our hearts beat- 

 ing and our stomachs at work. Did these things depend, 

 we will not say upon our efiort, but upon our bidding, our 

 care, or our attention, they would leave us leisure for noth- 

 ing else. We must have been continually upon the watch, 

 and continually in fear ; nor would this constitution have 

 allowed of sleep. 



It might perhaps be expected that an organ so precious, 

 yi such central and primary importance as the heart is, 

 should be defended by a ca?,e. The fact is, that a membra 

 nous purse or bag, made of strong, tough materials, is pro- 

 vided for it ; holding the heart within its cavity ; sitting 

 loosely and easily about it ; guarding its substance, without 

 confining its motion ; and containing likewise a spoonful or 

 two of water, just sufficient to keep the surface of the heart 

 in a state of suppleness and moisture. How should such a 

 loose covering be generated by the action of the heart ? Does 

 not the enclosing of it in a sack, answering no other pur- 

 pose but that enclosure, shov/ the care that has been taken 

 of its preservation ? 



One use of the circulation of the blood probably, among 

 other uses, is, to distribute nourishment to the difierent 

 parts of the body. How minute and multiplied the ramifi- 

 cations of the bloodvessels for that purpose are, and how 

 thickly spread over at least the superficies of the body, is 



