two solutions, in one of which the blood preponderated, in the other, water. The results were as follows:Blood drawn at the same time coagulated naturally in five minutes; the blood largely diluted with water coagulated more firmly in the same time; while the blood containing the small proportion of water was fluid. for eight minutes, and at last formed only a feeble clot. A similar experiment has been recorded by Mr. Blake.

These results have a bearing on experiments XXXVI to XL, where water, thrown into the system in large quantities, produced fluidity of blood.

[Production of Coagulation in Blood Surcharged with Ammonia. I have shown in preceding experiments, that when excess of ammonia is added to blood, such blood remains permanently fluid at ordinary temperatures. It also acquires a dark colour on exposure to the air, and rapidly absorbs carbonic acid. But this blood, thus held fluid by the excess of its solvent, may be made to coagulate in ways very simple and striking. Addition of water at 96° is one mode by which this change can be established. Experiments CCCLXI to CCCLXIII illustrate this fact without further comment. The addition of very dilute solutions of acids leads to the same result. Exposure of such blood for some time in the water bath at 98° Fahr. is sufficient to ensure coagulation if the proportion of ammonia added be slight, and the blood be not excluded from the air.

EXPERIMENT CCCXC. Coagulation of Blood held Fluid for Twenty Hours, by Exposure to a Temperature of 98° Fahr. I placed in a bottle five hundred grains of white of egg, together with a quarter of a grain of ammonia in solution with two drachms of water. I then received into the same bottle five hundred grains of

mixed blood from the neck of an ox. Shaking these solutions together, I carefully stoppered the bottle containing them, and placed it in water at 32° Fahr. until such time as I could manage the following details.

I took a piece of glass tubing of half inch bore, closed it at one end like a test-tube, and then cut it to such a length that it would just hold the thousand grains of solution named above. This being done, I poured the solution into the glass tube, hermetically closed it, and set it aside in the perpendicular position at a temperature of 60° Fahr. In the course of one hour the bloodcorpuscles began to sink, and in twenty hours they were all congregated in the lower three inches of the tube. I now filed a small hole in the tube at a line one inch above the corpuscles, and, re-opening the tube at the top, decanted off the upper and clear liquor. This was a viscid feebly pink solution, and may be considered as a kind of liquor sanguinis.

Returning to the blood-corpuscles and the remaining solution in the lower part of the tube, I turned the whole into an evaporating dish, and added a part of the supernatant solution. There was no trace whatever of clot; and, on gentle stirring, the corpuscles again commingled with the surrounding fluid. I then placed the evaporating dish with its contents in the water bath at 98° Fahr., gently stirring up the fluid occasionally. Ammonia was steadily evolved. In four hours feeble coagulation had occurred; and in six hours the whole was an uniform dark coagulum, from which no serum exuded.

But the most interesting fact in this matter is, that superammoniated blood may be made to coagulate by the very cautious addition of the fixed alkalies.

or of the hydrate of lime. I subjoin experiments bearing on this demonstration.

EXPERIMENT CCCXCI.

Coagulation of Blood held Fluid by Ammonia on Addition of Potassa. One hundred grains of blood from the neck of a sheep were received into a bottle containing one-twentieth of a grain of ammonia with two minims of water. The bottle was kept securely closed; and, twenty-four hours afterwards, the blood was found as fluid as at the moment when it was drawn. I now added to the blood one-twentieth of a grain of hydrate of potassa, and set the blood in a water-bath at 98° Fahr. It evolved ammonia feebly; and in two hours it had commenced to thicken, and soon set in a firm natural clot, modeled to the capsule containing it, and resembling in every way a recently formed natural coagulum. A little serum exuded. Another portion of the ammoniated blood, left simply exposed to the air, remained permanently fluid.

EXPERIMENT CCCXCII. Coagulation of Blood held Fluid by Ammonia on Addition of Lime. Sixty grains of mixed blood from the neck of a sheep were placed in a capsule containing one-twentieth of a grain of ammonia with three minims of water. This blood was thus rendered permanently fluid at ordinary temperatures, and soon acquired a dark colour. After twenty-four hours had elapsed, I added to it one half-drachm of water recently saturated with lime, and then placed it in its capsule in a water-bath at 98° Fahr. Ammonia was evolved; and in three hours the blood had set in a beautiful firm clot, which was modeled to the vessel: a considerable quantity of serum exuded from it, and it resembled in every way a recently and spontaneously formed coagulum.

EXPERIMENT CCCXCII. Coagulation of Blood held

Fluid by Ammonia on Addition of Lime. One hundred grains of mixed blood from the neck of a sheep were received into a bottle containing one-tenth of a grain of ammonia with six minims of water. The blood remained fluid for twenty-four hours, exposed to the air at 60° Fahr.; it also acquired a dark colour. At the end of this time, I took a grain of unslaked lime, slaked it, and made it into milk of lime with five minims of water. I then added the milk of lime to the blood in an open cup, setting the cup in a water-bath at 98°. Ammonia was now distinctly evolved; and in four hours. the blood had formed a dark feeble coagulum, from which serum exuded. Another hundred grains of blood from the same animal, which had been treated with ammonia in the same proportion, and which was simply left at rest at the same temperature (98°) did not coagulate.

In these experiments, especially if potassa or soda be employed as the displacing agent, the greatest delicacy is required. For, if too much of the alkali be added, it not only displaces the ammonia, but takes its place, and the fibrin is dissolved by the fixed alkali. This event, while it leads to apparent failure in many experiments, may be avoided with proper care. During the experiment, the blood should be kept at 98° Fahr.

Re-solution and Recoagulation of Blood-Clot. When once blood has coagulated, or when fibrin has been removed in the separate state, rapid re-solution either of red clot or simple fibrin is exceedingly difficult. This is due apparently to mere physical causes,―i. e., the particles of fibrin come so closely and compactly together after their precipitation, that the solvent enters

into contact with a limited surface only of the substance to be dissolved. Thus time is required; and although in time solution is produced, the production of the solution is attended with changes in the fibrin which destroy in a great measure its ordinary and normal properties. The same modification is produced if the fibrin be evaporated to dryness, and be afterwards redissolved in an alkaline solvent. In the circulating blood, matters are arranged in a way which is inimitable out of the body. Bostock expresses with great force the conditions in the body, when he speaks of the fibrin being added, as it were, particle by particle; but he does not here express the whole fact, for it is probable, if not absolutely demonstrable, that the fibrin is never in other than in a fluid or semifluid condition during healthy life.

From these causes, the re-solution and recoagulation of blood-clot or of fibrin, per se, is an experiment not so easily done as might, a priori, be presumed from a perusal of the foregoing experiments. I have, however, seen this accomplished; first by accident or rather empirical experiment, and afterwards by a more accurate and systematic process. A few examples will convey the results of the researches which I have made on this subject.]

EXPERIMENT CCCXCIV. Solution and Recoagulation of Coagulated Fibrin. An assistant once brought to me from Mr. Mavor, the veterinary surgeon, eight ounces of blood which had been drawn from the jugular vein of a horse. The blood had coagulated slowly, giving a buffy coat an inch in thickness, which completely filled at its upper part the diameter of the long narrow vessel into which the blood had been received. The blood was thus spontaneously divided into two portions: the solid