a history of science-4-第17章
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he blood…supply on the opposite sides of the neck played in the process of development； or； perhaps more correctly； to see what effect cutting off the main blood…supply would have； Hunter had one of the deer of Richmond Park caught and tied； while he placed a ligature around one of the carotid arteriesone of the two principal arteries that supply the head with blood。 He observed that shortly after this the antler （which was only half grown and consequently very vascular） on the side of the obliterated artery became cold to the touchfrom the lack of warmth…giving blood。 There was nothing unexpected in this； and Hunter thought nothing of it until a few days later； when he found； to his surprise； that the antler had become as warm as its fellow； and was apparently increasing in size。 Puzzled as to how this could be； and suspecting that in some way his ligature around the artery had not been effective； he ordered the deer killed； and on examination was astonished to find that while his ligature had completely shut off the blood…supply from the source of that carotid artery； the smaller arteries had become enlarged so as to supply the antler with blood as well as ever； only by a different route。
Hunter soon had a chance to make a practical application of the knowledge thus acquired。 This was a case of popliteal aneurism； operations for which had heretofore proved pretty uniformly fatal。 An aneurism； as is generally understood； is an enlargement of a certain part of an artery； this enlargement sometimes becoming of enormous size； full of palpitating blood； and likely to rupture with fatal results at any time。 If by any means the blood can be allowed to remain quiet for even a few hours in this aneurism it will form a clot； contract； and finally be absorbed and disappear without any evil results。 The problem of keeping the blood quiet； with the heart continually driving it through the vessel； is not a simple one； and in Hunter's time was considered so insurmountable that some surgeons advocated amputation of any member having an aneurism； while others cut down upon the tumor itself and attempted to tie off the artery above and below。 The first of these operations maimed the patient for life； while the second was likely to prove fatal。
In pondering over what he had learned about collateral circulation and the time required for it to become fully established； Hunter conceived the idea that if the blood…supply was cut off from above the aneurism； thus temporarily preventing the ceaseless pulsations from the heart； this blood would coagulate and form a clot before the collateral circulation could become established or could affect it。 The patient upon whom he performed his now celebrated operation was afflicted with a popliteal aneurismthat is； the aneurism was located on the large popliteal artery just behind the knee…joint。 Hunter； therefore； tied off the femoral； or main supplying artery in the thigh； a little distance above the aneurism。 The operation was entirely successful； and in six weeks' time the patient was able to leave the hospital； and with two sound limbs。 Naturally the simplicity and success of this operation aroused the attention of Europe； and； alone； would have made the name of Hunter immortal in the annals of surgery。 The operation has ever since been called the 〃Hunterian〃 operation for aneurism； but there is reason to believe that Dominique Anel （born about 1679） performed a somewhat similar operation several years earlier。 It is probable； however； that Hunter had never heard of this work of Anel； and that his operation was the outcome of his own independent reasoning from the facts he had learned about collateral circulation。 Furthermore； Hunter's mode of operation was a much better one than Anel's； and； while Anel's must claim priority； the credit of making it widely known will always be Hunter's。
The great services of Hunter were recognized both at home and abroad； and honors and positions of honor and responsibility were given him。 In 1776 he was appointed surgeon…extraordinary to the king； in 1783 he was elected a member of the Royal Society of Medicine and of the Royal Academy of Surgery at Paris； in 1786 he became deputy surgeon…general of the army； and in 1790 he was appointed surgeon…general and inspector…general of hospitals。 All these positions he filled with credit； and he was actively engaged in his tireless pursuit of knowledge and in discharging his many duties when in October； 1793； he was stricken while addressing some colleagues； and fell dead in the arms of a fellow…physician。
LAZZARO SPALLANZANI
Hunter's great rival among contemporary physiologists was the Italian Lazzaro Spallanzani （1729…1799）； one of the most picturesque figures in the history of science。 He was not educated either as a scientist or physician； devoting； himself at first to philosophy and the languages； afterwards studying law； and later taking orders。 But he was a keen observer of nature and of a questioning and investigating mind； so that he is remembered now chiefly for his discoveries and investigations in the biological sciences。 One important demonstration was his controversion of the theory of abiogenesis； or 〃spontaneous generation；〃 as propounded by Needham and Buffon。 At the time of Needham's experiments it had long been observed that when animal or vegetable matter had lain in water for a little timelong enough for it to begin to undergo decompositionthe water became filled with microscopic creatures； the 〃infusoria animalculis。〃 This would tend to show； either that the water or the animal or vegetable substance contained the 〃germs〃 of these minute organisms； or else that they were generated spontaneously。 It was known that boiling killed these animalcules； and Needham agreed； therefore； that if he first heated the meat or vegetables； and also the water containing them； and then placed them in hermetically scaled jarsif he did this； and still the animalcules made their appearance； it would be proof…positive that they had been generated spontaneously。 Accordingly be made numerous experiments； always with the same resultsthat after a few days the water was found to swarm with the microscopic creatures。 The thing seemed proven beyond questionproviding； of course； that there had been no slips in the experiments。
But Abbe Spallanzani thought that he detected such slips in Needham's experiment。 The possibility of such slips might come in several ways： the contents of the jar might not have been boiled for a sufficient length of time to kill all the germs； or the air might not have been excluded completely by the sealing process。 To cover both these contingencies； Spallanzani first hermetically sealed the glass vessels and then boiled them for three…quarters of an hour。 Under these circumstances no animalcules ever made their appearancea conclusive demonstration that rendered Needham's grounds for his theory at once untenable。＇2＇
Allied to these studies of spontaneous generation were Spallanzani's experiments and observations on the physiological processes of generation among higher animals。 He experimented with frogs； tortoises； and dogs； and settled beyond question the function of the ovum and spermatozoon。 Unfortunately he misinterpreted the part played by the spermatozoa in believing that their surrounding fluid was equally active in the fertilizing process； and it was not until some forty years later （1824） that Dumas corrected this error。
THE CHEMICAL THEORY OF DIGESTION
Among the most interesting researches of Spallanzani were his experiments to prove that digestion； as carried on in the stomach； is a chemical process。 In this he demonstrated； as Rene Reaumur had attempted to demonstrate； that digestion could be carried on outside the walls of the stomach as an ordinary chemical reaction； using the gastric juice as the reagent for performing the experiment。 The question as to whether the stomach acted as a grinding or triturating organ； rather than as a receptacle for chemical action； had been settled by Reaumur and was no longer a question of general dispute。 Reaumur had demonstrated conclusively that digestion would take place in the stomach in the same manner and the same time if
