longing the fine extremity of one of these tubes to the length of three or four inches, each minute drop of blood, as it is drawn through this capillary course, is so acted on by the exhausting force that it coagulates, and the passage of blood may thus be stopped at the outset.]

Coagulation of flowing Blood in Streams of different Diameters. The fact has been known for ages past, that if, in the operation of phlebotomy, the puncture in the vein be small, the thin blood-stream soon stops, from coagulation occurring at the wound; while such blood as it is caught coagulates with great rapidity. In bleeding, I have seen the blood, when the current has been slow and thin, coagulate as it trickled down the arm of the patient, or fell on my own hand. On the other side, when a full and free stream of blood is drawn, it continues in the current until it is stopped from failure in the force of the circulation; while the mass of blood received into the basin coagulates slowly in comparison.

By a very simple instrument I found myself able to imitate this occurrence, and to see at a coup d'œil the result of the thin and broad blood streams on coagulation. I had made a cylinder of tin, eight inches long and four inches in diameter. This cylinder was closed at the lower end, and open at the top. At the lower part in the side wall I inserted, at different points of the circumference, four tubes, which stood out at right angles from the vessel, and took a gentle spout curve. The ends of these tubes within the tin cylinder measured the same, viz. a quarter of an inch in diameter; but at the other or projecting ends, each tube was brought to a different diameter; one was left at the quarter-inch bore; another was drawn out to an eighth of an inch; the third

to the sixteenth of an inch; the fourth to the thirtysecond of an inch. The instrument, when in use, was raised on a pedestal, so that a beaker could be placed beneath each spout; then the large tin cylinder was filled with freshly drawn blood, which discharged itself into the beakers in currents of different diameters, as shewn in the subjoined diagram.

EXPERIMENT CXXXIII.

Transmission of Blood through

Tubes of different Diameters. I received a quart of blood from the neck of a bullock, and from it filled the large cylinder. The blood ran out in a full stream from the quarter-inch tube, and coagulated in a firm clot in one minute after being received into the beaker. The cur

rent through the eighth of an inch tube ran for a few seconds, then stopped altogether. The blood discharged. by this tube coagulated almost instantly after reaching the beaker beneath. Through the sixteenth of an inch tube no current at all was set up. A few drops only escaped, when a drop at the end of the tube coagulated and sealed up the aperture altogether. Through the thirty-second of an inch tube not one drop fell; the tube filled to its fine point at the first moment, but here the blood set, and the further flow was prevented.

EXPERIMENT CXXXIV. Transmission of Blood through Tubes of different Diameters. I received from the neck of a lamb a pint of freshly drawn blood, and instantly transferred it to the large cylinder. A brisk current immediately flowed through all the tubes. The current through the smallest tube stopped in ten seconds, its point being blocked up with a bead of coagulum. The current through the sixteenth of an inch tube stopped next in order; then that through the eighth of an inch tube. The blood received into the beaker beneath the quarter-inch tube remained so fluid when the beaker was full, that I poured it back into the reservoir. At the end of forty seconds from the first gush of blood through the tubes, the current through the quarter-inch tube failed from the formation of clot in the tube.

EXPERIMENT CXXXV. Transmission of Blood through Tubes of different Diameters. I received a charge of blood from the neck of a sheep, and instantly filled the large cylinder or reservoir. At first there was a free spirt of blood from all the tubes; but the current through the smallest stopped in three seconds from coagulation at the point. The current through the sixteenth of an inch bore stopped from the same cause

at twenty seconds. When the beaker beneath the quarter-inch tube was full of blood, the blood it contained was perfectly fluid, and was thus returned to the reservoir. At the end of forty seconds, the currents through the eighth of an inch and quarter-inch tubes stopped flowing from coagulation, the smaller of the two stopping first by the matter of a few seconds.

EXPERIMENT CXXXVI. Transmission of Blood through Tubes of different Diameters. I experimented in a similar way to that recorded in the last experiment, on the blood of another sheep. The results were the same, with the one exception that a continuous current was not set up from the smaller tube. As the first portion of blood escaped from this tube, a bead of coagulum was formed at the mouth and sealed it up completely.

EXPERIMENT CXXXVII. Transmission of Blood through Tubes of different Diameters. I received a charge of blood from the neck of a sheep, and at once transferred it to the large cylinder or reservoir. I kept up the supply in the reservoir by the addition of a new charge of blood from the animal, an assistant keeping watch on the currents from the tubes. The flow from the smallest tube was only a few drops, and ceased from coagulation within five seconds. The flow from the second smallest tube ceased next in order, and quickly; while the currents in the two larger tubes were continuous for one minute, and stopped nearly at the same time, from the tubes becoming blocked up with red clot.

EXPERIMENT CXXXVIII. Exposure of Blood to the Air in a Stream. I caught in a spouted jug a pint of blood from the neck of a sheep. One half of this was decanted into a beaker. The other half I poured in a slow

stream from the jug into a another similar jug, repeating the process. In twenty-five seconds I felt a clot passing from one vessel to the other. At the end of fifty seconds, an assistant noted that the blood left at rest was coagulated. On examining the blood which had been poured out, I found that the mode of coagulation had been by simple separation of the fibrin, as obtains when blood is whipped with the hand. The separation of fibrin in this experiment was very perfect, as as no coagulation whatever occurred when the fibrous mesh was removed from the fluid.

On the Effects of driving currents of Air through newly drawn Blood. The abstraction of air favours and hastens coagulation. The force of brisk currents of air through blood has precisely the same influence. I use the word air in this place, not because air only is implied, but because air was the compound gas usually employed in these inquiries, as being at once the readiest to hand and cheapest. The effects, however, are precisely the same, whether oxygen be the gas driven through, or nitrogen, or certain other gases, which I shall refer to further on, and which are negative in their chemical action on the blood when driven through it, but exert the ordinary physical effect of carrying with them other free gases with which they may come in contact in their course.

To be able to drive air through blood with equality of diffusion and freely, I constructed an apparatus, as shewn in the next drawing. It was simply a straight glass vessel, three inches in diameter, and eight inches in height; it was open at the top. A little below the middle part of this vessel was placed a circular tube, perforated with holes above, like a circular gas-burner;