128 EFFECTS OF RESPIRATION, &C. [BOOK I. 



space is again filled, but only to be emptied in a 

 similar manner. It is with a view to accelerate the 

 circulation through the veins, and to keep the blood 

 warm in winter, that mankind betake themselves 

 to forced exercises, as hunting, running, or beating 

 the arms athwart the chest, and that beasts with 

 the same propensity gambol and frisk about, or rub 

 themselves : both promote the same ends, by breath- 

 ing short, so as not to cool the lungs too much, 

 or by drawing in the same Warm air over again, in 

 sheltered situations. 



44. By the process just described, the blood 

 being once admitted into the minuter veins, finds 

 its way to the larger ones, which convey it to the 

 heart; near to which, as the quantity becomes 

 great in the large vein, it receives a powerful aux- 

 iliary in the filling and emptying of the lungs, and 

 the working forward and backward of the midriff, 

 as described before. Passing through it near the 

 back bone, and, consequently, at its more muscular 

 part, the great vein must, at every inspiration, re- 

 ceive from the midriff considerable aid in pouring 

 forth its contents — to say nothing additional of the 

 pump-like action of the heart itself. At this part 

 the vein acquires the appearance of a double tube, 

 the outside thickened and muscular, the inner one 

 membranous and collapsed, as if too big for the 

 space in which it is placed. But the curious fact — 

 how the blood which had been sent into circulation 

 through the arteries, gets into the veins at first, 

 deserves consideration : as this must be effected 



