NATURAL THEOLOGY. 181 



treme tenuity should be compensated by multi- 

 tude ; for a large quantity of chyle (in ordinary 

 constitutions not less, it has been computed, than 

 two or three quarts in a day) is, by some means 

 or other, to be passed through them. According- 

 ly, we find the number of the lacteals exceeding 

 all powers of computation, and their pipes so fine 

 and slender as not to be visible, unless filled, to 

 the naked eye, and their orifices, which open into 

 the intestines, so small as not to be discernible 

 even by the best microscope. Fourthly, the main 

 pipe, which carries the chyle from the reservoir 

 to the blood, viz., the thoracic duct, being fixed in 

 an almost upright position, and wanting that ad- 

 vantage of propulsion which the arteries possess, 

 is furnished with a succession of valves to check 

 the ascending fluid, when once it has passed them, 

 from falling back. These valves look upwards, 

 so as to leave the ascent free, but to prevent the 

 return of the chyle, if, for want of sufficient force 

 to push it on, its weight should at any time cause 

 it to descend. Fifthly, the chyle enters the blood 

 in an odd place, but perhaps the most commo- 

 dious place possible, viz., at a large vein in the 

 neck, so situated with respect to the circulation as 

 speedily to bring the mixture to the heart. And 

 this seems to be a circumstance of great moment; 

 for had the chyle entered the blood at an artery 

 or at a distant vein, the fluid composed of the old 

 and the new materials must have performed a 

 considerable part of the circulation before it re- 



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