Page:Philosophical Transactions - Volume 050, part 1.djvu/370

 Such was Boerhaave's doctrine concerning the vafcuiar fyftem of animal bodies; like many of hisother notions, ingenious, plaufible, and recommending itfelf, at firft light, by an appearance of geometrical and mechanical accuracy: but founded upon inefficient data, and by no means to be reconciled to appearances.

For, in the firft place, fhould we admit his hypothefts, it is certain, that the conical or converging form of the aorta, and the change of direction in its^ branches, muft, in the diftant blood-veftels, occafton a great reftftance to the moving blood, and a great diminution of its velocity. Suppofe that this refiftance be, in any capillary red artery, to the reftftance in the trunk of the aorta, as any larger affignable number is to unit: the reftftance, then, in a capillary ferousartery will, to that in the aorta, be as the fquare of that number is to unit; in the capillary lymphatic, as the cube; and fo in progreffion: that is, the velocity of the fluids, in the remoter l'eries of veffels,. will be, phyficially, nothing. But we know, on the contrary, that fome very remote feries of veffels have their contents moved with a very confiderable velocity; particularly the veffels of the infenftble perfpiration; and in anatomical injections, the liquor thrown into an artery fcarce returns more eafily or fpeedily by the eorrefponding vein, than by the moft fubtile excretory duCts. Moreover, there are an infinite number of obfervations of morbid cafes, in which the red blood itfelf has been evacuated thro' fome of the moft remote feries of veffels, merely from an occaftonal temporary obftruCtion in one part, or a praeter natural laxity in another; and without any