round each neck of the tube: next, the tube was filled with mercury through its entire length, and the whole was left at rest. Meanwhile, an assistant had taken the observation that the blood flowing from the divided vein of the sheep in question coagulated on exposure to the air, temperature 66° Fahr., in one minute and ten seconds.

It had been my intention not to disturb the blood buried under the mercury for six hours. But an accident occurred which prevented this intention. In moving the tube on its stand to a more convenient and safe position, some unnecessary hurry occurred, the tube got a shake and gave way at the bend, and the mercury escaped. This occurred three-quarters of an hour after the immersion of the vein. The accident was irremediable at the moment. I therefore placed the piece of vein, which luckily was uninjured, in a cup, and punctured it with a lancet. The blood flowed out quite fluid, but set into a firm clot, on exposure to the air, one minute and twenty seconds afterwards.

EXPERIMENT CLII. Blood enclosed in a Vein under Mercury. I laid bare the external jugular vein of a dog, ligatured it as in last experiment, and drew it under mercury in an instrument precisely similar to the one already described. The vein thus placed was left at rest for nine hours: it was then gently removed, placed in a cup, and punctured with a lancet. Its contained blood flowed out in a perfectly fluid condition, but coagulated in four minutes on exposure to the air. A little blood, caught from the vein of this animal directly after the operation to which he had been subjected, coagulated firmly in three minutes on exposure to the air.

EXPERIMENT CLIII. Blood enclosed in a Vein under Mercury. I laid bare the external jugular of a cat, placed an inch of it between two ligatures, removed the ligatured part, and drew it under the mercury as before. This blood was thus left for twenty hours: the vein was then gently withdrawn, placed in a spoon, and punctured. Its contained blood flowed out entirely fluid, and on exposure to the air coagulated firmly in four minutes. Some blood of this same animal, derived also from the jugular vein at the time of operation, coagulated, on exposure to the air, in two minutes and a half.

Writers on natural history, in referring to the medicinal leech, are accustomed to state the fact, that the blood drawn by the leech remains fluid in its body, and serves for its nourishment for long intervals of time. Cuvier remarks, that the blood swallowed by the leech continues red and without alteration for several weeks; and Griffiths (Animal Kingdom, part 35, p. 129), says that in the leech the process of digestion is extremely slow, and that a single meal of blood will suffice for many months, during all which period "so much of the blood as remains undigested in the stomach continues in the fluid state and as if just taken in, notwithstanding the vast difference in the heat of the body of a mammiferous animal and that of a leech.

It is clear that in writing this passage, Mr. Griffiths laboured under the erroneous idea that this fluidity of blood is due to the presence of heat. The fact, however, about the leech is of interest, and the study of it has some points bearing on coagulation. is allowed to engorge itself, and is then removed and emptied of its blood by firm pressure with the finger

If a leech

and thumb, the blood thus extracted will be found quite fluid, and its power of coagulation exceedingly feeble, and in some cases nil. I have seen slight coagulation in the blood thus obtained from leeches, but I have also seen the blood so obtained perfectly uncoaguable. I have observed also that leech-bites continue to bleed for a much longer period than do wounds. from a lancet point made in the same individual at the same time; while the first blood which flows from the bite after the removal of the leech continues uncoagulable for a very long time, and is even in some cases also uncoagulable. This fact accounts for the difficulty which not unfrequently occurs in the stopping of the bleeding from leech-bites. It is not until the blood has flowed away for some minutes, that a coagulable current is supplied.

The cause of this simple but striking phenomenon is not very easily explained. The first inference on my mind was, that in the body of the leech the blood meets with some solvent secretion which holds it permanently fluid, or else that in the mechanical act of abstracting the blood some change occurs, some kind of defibrination. To follow these questions, I made a few simple experiments on leech-drawn blood.

EXPERIMENT CLIV. Observation on Leech-drawn Blood. I laid a leech on the arm of a gentleman who was in perfect health. The leech filled itself with blood, and fell off of its own accord. As soon as it removed itself, I emptied it of its contained blood by traction. The blood was dark and entirely fluid. This blood remained fluid on exposure to the air (temperature 65°) in a shallow cup, for nine hours; after this it became a little thicker and more glutinous, but it never underwent the proper process of coagulation.

EXPERIMENT CLV. Observation on Leech-drawn Blood. I laid another leech on the arm of the same gentleman, and allowed it to draw blood until it fell off of its own free will. As soon as this occurred, I removed its contained blood by laying its body freely open with a lancet. The blood was received into a spoon, into which it flowed freely. This blood was set aside, exposed to the air at a temperature of 65° Fahr., and closely observed. It remained fluid for nearly two hours, then became slightly glutinous, and at the end of four hours presented a few feebly formed clots. Eventually it formed a loose coagulum, resembling thin black currant jelly.

After the leech was removed from the arm, the wound it had produced continued to give out blood very freely. I caught the blood thus flowing at different intervals, allowing it to trickle into teaspoons of the same size and shape. The results were curious. The blood which was received into the first spoon, and which was collected immediately after the removal of the leech, was dark, and showed the same feebleness of coagulation as the blood taken from the leech itself. Another portion of blood received into a second spoon five minutes later, coagulated in twenty-five minutes with moderate firmness. A third portion of blood, caught ten minutes later still, coagulated in eight minutes; while at the end of half an hour the blood which still flowed from the wound coagulated firmly, and in fine red clots, in two minutes. Ultimately the blood coagulated as it slowly oozed from the wound, and so the wound itself was sealed up.

I laid two leeches on the arm of the same gentleman. They took hold nearly at the same moment, and filled to engorgement.

EXPERIMENT CLVI. Observation on Leech-drawn Blood. I received one of the leeches as it fell off into a glass plate, and at once placed round it, a few lines from its mouth, a firm ligature. It was thus prevented from ejecting its contained blood; in this condition it was placed securely in an empty beaker, and left exposed to the air, the mean temperature of which, during the experiment, was 62° Fahr. For two days the leech, by its occasional movement, showed signs of life, and it was therefore left untouched. On the morning of the third day it was found quite dead, and its body stiffened and dry. I laid open the body with a scalpel, and found the contained blood universally coagulated. The clots were dark, but uniform and firm.

EXPERIMENT CLVII. Observation on Leech-drawn Blood. The second of the leeches referred to above, after its removal from the arm, was ligatured as in the preceding case, so as to prevent the ejection of its contained blood. A second ligature was also carried round its body at its tail extremity. Thus fixed, the body of the leech was drawn under mercury in the heat tube instrument, delineated and described at pages 202-3, and was thus left for the space of nine clear days, during which the temperature of the room was never lower than 60° Fahr. All movement ceased almost instantly after the immersion in the mercury. On the morning of the tenth day the leech was withdrawn from the mercury, and its body was laid open. The body was filled with blood, which was entirely fluid. There was no trace or indication of coagulum. This blood, received into a small evaporating dish, and exposed to the air at a temperature of 65°, underwent slow coagulation, and at the end of six hours was in the form of broken