TRANSFUSION OF BLOOD bad results of the earlier operations, in which the blood of the sheep had been introduced into the veins of the human subject. This fact was still further elaborated by subsequent ex- perimenters. If the animals used for experi- ment belong to different classes, as where the blood of a quadruped is introduced into the veins of a bird, or that of a bird into the veins of a quadruped, even in small quantity, it ap- pears to have an actually poisonous effect, and death follows in a very short time. If the animals belong to the same class, but are not of the same genus, as where the blood of the cow or the sheep is introduced into the vessels of the cat or the rabbit, or human blood into those of the dog, there is a temporary reani- mation, but noxious effects afterward follow, and death occurs at the end of some days. These noxious results appear to be due in great measure to the presence of the fibrine of the blood ; for if this be removed by beating the fresh blood before its injection, they do not follow, or at least are much less strongly marked. Nevertheless, the blood of animals belonging to a different class, even when de- fibrinated, though no longer actually poison- ous, does not resuscitate or preserve the animal experimented on from the effects of haemor- rhage. To secure this beneficial effect, the animals must be within certain limits of con- sanguinity. If the blood be used fresh, they must belong to the same species ; and if it be defibrinated, they must still belong to the same genus. Furthermore, it is found that the red globules of the blood are essential to its vivify- ing influence. The fibrine may be removed without injury, and in some cases, as above mentioned, even with benefit. But the injec- tion of serum alone, that is, blood deprived of both fibrine and globules, is useless as a means of preserving life. With these improvements the operation of transfusion has been success- fully applied to the human subject. After an abundant hasmorrhage there is frequently an interval, often of several hours, during which, although the haemorrhage may have ceased, the patient is evidently sinking, and other means of restoration are of no avail. It is to such cases that the operation of transfusion is adapted. B6rard has recorded 14 instances of this kind, most of them cases of haamor- rhage after delivery, in which the life of the patient was saved by this means. There are certain rules which it is important to observe : 1. In transfusion in the human subject, it is of course human blood that should be used, supplied by a healthy, vigorous person. 2. But a small quantity, namely, from two to four ounces, should be injected at a time. This amount is generally sufficient ; if not, the in- jection may be repeated after an interval. All that is required by the transfusion is to restore the patient to consciousness and bring him into such a condition that he can take and appro- priate nourishment and stimulus. 3. If the in- jection be made by a syringe, great care should TRANSIT 841 be taken that the blood be not allowed to fall below its natural temperature of 100 F., and especially that no bubbles of air become entangled with it and thus introduced into the veins. 4. The injection should be made slowly, and terminated as soon as the requisite effect has been produced. 5. The delay should not be so great as to incur the risk of the blood becoming coagulated, either in the syringe or within the veins of the patient. TRANSIT, in astronomy, the passage of a planet across the disk of the sun, or of a satel- lite across the disk of its primary ; also, the passage of a heavenly body across the meridian of the place of observation, sometimes called its culmination. Of the planets, only Mercury and Venus, having orbits within the orbit of the earth, can present this phenomenon. The transits of Venus are employed for the deter- mination of the sun's distance; .they recur at alternate intervals of 8 and 105$, and 8 and 121 years. The earliest transit of the sun's disk of which we have an account is that of Venus in 1639, predicted and observed by Jere- miah Horrox, an amateur astronomer of Lan- cashire, England. The transits of the last century, in the years 1761 and 1769, were ob- served with great care, expeditions having been equipped for the purpose by the chief Euro- pean states. But the results then obtained were not so trustworthy as had been antici- pated. Two methods of observation were relied on, both depending on time, though not in the same way. It had been suggested by Halley, early in the century, that instead of observing the position of Venus on the sun's face at any assigned instant (for the purpose of thence determining her relative parallactic displacement and so her distance), the observ- ers should note the interval of time occupied by the planet in completing her transit. As the effect of parallax would be to cause her to traverse different chords, as seen by observers at northern and at southern stations, there would result a difference in the duration of transit, the amount of which would enable astronomers to deduce the sun's distance. De- lisle, when the transit of 1761 was approach- ing, discovered that there would be on that occasion disadvantages in applying Halley's proposed method, which requires that both the beginning and end of the transit should be seen; and he proposed another method, re- quiring only that one or other of these phases should be noted. According to this plan, two observers were both to note the beginning (or else both to note the end), one observing the phase where it occurred as early as possible, and the other observing it where it occurred as late as possible ; then, by noting the differ- ence of time between their two observations, they would be able to estimate the sun's dis- tance. Halley's method was manifestly the easier, since each observer had to note the du- ration between two phenomena both of which were observed by him, and the difference be-
