LETTERS. 601
which we observe in the conjunction between the ureters and the bladder, and of the biliary duct with the duodenum. The ureters insinuate themselves obliquely and tortuously be- tween the coats of the bladder, without anything in the nature of an anastomosis, yet in such a manner as occasionally affords a passage to blood, to pus, and to calculi ; it is easy, moreover, to fill the bladder through them with air or water ; but by no effort can you force anything from the bladder into them. I care not, however, to make any question here of the etymo- logy of words ; for I am not of opinion that it is the province of philosophy to infer aught as to the works of nature from the signification of words, or to cite anatomical disquisitions before the grammatical tribunal. Our business is not so much to inquire what a word properly signifies, as how it is com- monly understood ; for use and wont, as in so many other matters, are greatly to be considered in the interpretation of words. It seems to me, therefore, that we are to take especial care not to employ any unusual words, or any common ones already familiarly used, in a sense which is not in accordance with the meaning we purpose to attach to them. You indeed counsel well when you say, " only make sure of the thing, call it what you will." But when we discover that a thing has hitherto been indifferently or incorrectly explained (as the sequel will show it to have been in the present case), I do not think that the old appellation can ever be well applied to the new fact ; by using the old term you are apt to mislead where you desire to instruct. I acknowledge, then, a transit of the blood from the arteries, into the veins, and that occasionally immediate, without any intervention of soft parts ; but it does not take place in the manner hitherto believed, and as you yourself would have it, where you say that anastomoses, cor- rectly speaking, rather than an anastomosis, were required, namely, that the vessels may be open on either hand, and give free passage to the blood hither and thither. And hence it comes that you fail in the right solution of the .question, when you ask how it happens that with the arteries as patent or per- vious as the veins, the blood nevertheless flows only from the former into the latter, never from the latter into the former ? For what you say of the impulse of the blood through the arteries does not fully solve the difficulty in the present in-
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