[50] But there is a still more egregious blunder, and this the more surprising as it has been very general among physiologists, viz. that when an artery branches into two the capacity of the branches taken together is greater than that of the trunk. This would make the whole arterial system one continued _aneurism_,[51] and, instead of promoting the circulation of the blood, would in the most effectual manner prevent it. In what manner an error so extraordinary in its nature could pass the mathematical physicians of the last century, I cannot imagine; but certain it is, that, in the year 1780 or 1781, the Edinburgh College were schooled on this subject by one of their own students named _John Theodore Vander Kemp_, a Dutchman. This gentleman found, by accurate mensuration, that when an artery divides, if the diameters of the two branches are made the two shorter sides of a right-angled triangle, the diameter of the trunk will be the hypothenuse; and thus, as the areas of circles are to one another in proportion to the squares of their diameters, the sum of the areas of the two branches will be equal to the area of the trunk. On looking into Blumenbach’s physiology, I find the same remark. [51] An aneurism is a preternatural enlargement of an artery. The blood stagnates in that place, and at length eats through the flesh and skin. It is true, indeed, that this objection will in some degree hold, even though we suppose all the cavities of the heart to be equal, and the capacities of the blood vessels to be perfectly uniform throughout the whole body. For, if we suppose the blood to be at all condensed in the lungs by the coldness of the atmosphere, it must undoubtedly follow, that while passing from them it occupies less space than before it arrives at them. Hence the pulmonary vein, the left auricle of the heart, the left ventricle, the aorta, and all the rest of the arteries for a considerable way, must be comparatively empty, even though they receive as much fluid as fills the vena cava, right auricle and ventricle of the heart, and pulmonary artery. The equality which ought to prevail in the system, and which indeed cannot be dispensed with, can only take place in those remoter branches of the arteries in which the blood has reassumed its former state of dilation or rarefaction.