Читать книгу Harvey's Views on the Use of the Circulation of the Blood - John Green Curtis - Страница 6

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That Harvey frequently took refuge in speculation need excite no surprise. In the seventeenth century, even with his extraordinary contributions of observed fact to the knowledge of the circulation of the blood, the paucity of physiological knowledge in general and of experimental methods was so great that at every turn a thinking man was tempted to fill in the gaps with that which was beyond his powers of ocular demonstration. Contemplation of the circulation, indeed, led Harvey into contemplation of widely diverse problems of the life process. The feeding of the tissues, the significance of respiration, the cause of the heart-beat, the relative importance of the heart and the blood in the bodily hierarchy, the bodily heat and its source, and the seat of the soul—to these and other topics he gave much attention, and these we must consider. Let us begin with the circulation and its relation to the feeding of the tissues.

In the chapter of Harvey's book which follows at once upon the brief qualitative statement quoted at the end of our last chapter, Harvey himself brings us face to face with the difficult quantitative question raised by his triumphant proof of the circulation. He says:—

"The blood under the influence of the arterial pulse enters and is impelled in a continuous, equable, and incessant stream into every part and member of the body, in much larger quantity than were sufficient for nutrition or than the whole mass of fluids could supply."[10]

Here we see that the rapid renewal of the blood in "every part and member of the body" presented itself to Harvey's own mind as calling for some other explanation than the simple feeding of the tissues. The question of "cui bono" which his discovery raised is still but incompletely answered; in Harvey's day it was almost unanswerable. In dealing from time to time with its main features he himself, as we shall see, could only bring forward inadequate observations and shift his ground from one erroneous doctrine to another. In justice to his opponents, who seem to us so unreasonable, let us remember how prodigious this new question of "cui bono" must have seemed when the circulation itself was a novelty. Let us remember also that for nearly two thousand years the tissues had been held to feed themselves tranquilly out of the contents of the vessels in a way fitly expressed by the old simile of irrigation ditches in a garden—a simile which Aristotle and Galen had borrowed in turn from Plato.[11]

But if Harvey saw only too well that the feeding of the tissues could not explain the circulation, he had at least seen plainly how the doctrine of the circulation clarified the ancient but current doctrine as to the absorption of the digested food. The portal vein had been accepted as the route of this absorption. No doubt both Aristotle and Galen had seen its ruddy contents; at any rate both had concluded that the chyle was changed within the portal vein into a crude approximation to blood.[12] That the same vessel should carry to the liver altered chyle, and from the liver blood to nourish the stomach and intestines, had involved a difficulty which Galen had met with characteristic cleverness. He had cited in support of such a reversal of flow the flow of the bile into the gall-bladder and out by the same duct, the movement of food and vomit into and out of the stomach by the œsophagus, and the relation of the os uteri to impregnation and parturition.[13] Harvey says:—

"For the blood entering the mesentery by the cœliac artery and the superior and inferior mesenteries proceeds to the intestines, from which along with the chyle that has been attracted into the veins it returns by their numerous ramifications into the vena portæ of the liver, and from this into the vena cava, and this in such wise that the blood in these veins has the same colour and consistency as in other veins, in opposition to what many believe to be the fact. Nor need we hold the improbable belief that two inconveniently opposed movements take place in the whole capillary ramification, namely, movement of the chyle upward, of the blood downward. Is not the thing rather arranged as it is by the consummate providence of nature? For were the chyle mingled with the blood, the crude with the concocted in equal proportions, the result would not be concoction, transmutation, and sanguification, but rather, because they are reciprocally active and passive, a mixture, their union with one another producing something intermediate, precisely as when wine is mixed with water and [in] vinegar and water [oxicratum]. But when a minute quantity of chyle is mingled with a large quantity of blood flowing by, a quantity of chyle that bears no notable proportion to the blood, the effect is the same, as Aristotle says, as when a drop of water is added to a cask of wine, or the contrary; the resulting total is not a mixture, but is either wine or water. So in the dissected mesenteric veins we do not find chyme or chyle and blood, separate or mingled, but only blood, sensibly the same in color and consistency as in the rest of the veins."[14]

In a second passage of the same chapter,[15] Harvey returns to this subject; and again, twenty-one years later, in his first exercise to Riolanus, as follows:—

"Our learned author mentions a certain tract of his on the Circulation of the Blood: I wish I could obtain a sight of it; perhaps I might retract. But had the learned writer been so disposed, I do not see but that, having admitted the circular motion of the blood (and in the veins, as he says in the eighth chapter of the third book,[16] the blood incessantly and naturally ascends, or flows back, to the heart, as in all the arteries it descends or departs from the heart), all the difficulties which were formerly felt in connection with the distribution of chyle and the blood by the same channels are brought to an equally satisfactory solution; for all the mooted difficulties vanish when we cease to suppose two contrary motions at once in the same vessels, and admit but one and the same continuous motion in the mesenteric vessels from the intestines to the liver."[17]

From this passage we see, in passing, that Harvey at the age of seventy made little account of Caspar Aselli's discovery of the lacteals, published twenty-two years before in 1627,[18] the year before the announcement of the discovery of the circulation. Harvey's mind was focused on the blood, its motion and its meaning; this was to him the subject of prime importance. The ancient doctrine of the feeding of the tissues provided an insufficient reason for the existence of what his observations and his experiments revealed to him.