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are simply serous in character. This very marked distinction led me to test the relative effects of carbonate of ammonia and of urea on blood recently drawn; the following short record of the experiences thus obtained includes the facts of this inquiry.

Mixed blood drawn from the neck of an ox was used for the experiment: the natural period of coagulation of two thousand grains of this blood was six minutes.

Two thousand grains of the blood was received into a cup containing four grains of ammonia in one fluiddrachm of water. The blood thus treated, when left at rest, remained permanently fluid, and of port wine consistency. On agitation, fibrine could not be whipped out; nevertheless, on addition of caustic baryta at 60°, a portion of this blood readily coagulated with free evolution of ammonia. Examined microscopically, the corpuscles were found almost entirely dissolved.

At the same time, and from the same animal, two thousand grains of blood were received into a bottle containing four grains of urea in one fluid-drachm of water: this blood coagulated in nine minutes. The clot was unusually dark and jelly-like; the corpuscles underwent very little change, until decomposition commenced.

At the same time, two thousand grains more of the blood were drawn into a cup containing eight grains of urea in a fluid-drachm of water. This blood coagulated within a few seconds of nine minutes; it : formed also a dark softish clot, and its corpuscles

underwent no peculiar modification prior to putrefaction.

Into another cup there were received two thousand grains of blood; this cup contained sixteen grains of urea, in solution with one drachm of water. The blood coagulated a few seconds earlier than the specimen which was left to coagulate normally ; its corpuscles underwent no modification, and the clot formed, though very dark, was moderately firm.

Lastly, two thousand grains of blood from the same animal were caught in a cup containing thirtytwo grains of urea dissolved in a drachm of water. Coagulation occurred in five minutes, the clot being dark but firm, and yielding an abundance of serum. The corpuscles were unaltered so long as the mass remained free from putrefaction.

Thus, in respect to the physical effects of urea on blood, we learn the curious fact, that the salt in its concentrate form has no power to hold the blood fluid; but that reduced or diluted it does hold the blood temporarily fluid, although not to the same extent of fluidity as is so often met with in uræmia. This truth elicited, it was necessary to determine the effects of more dilute solutions of urea on blood. For this purpose I selected the blood of sheep, because the effects are more rapidly determined, and the influence of solvent bodies are more thoroughly brought out: the results are herewith given.

Into a cup capable of holding 2000 grains, four grains of urea were placed, dissolved in four fluiddrachms of distilled water. Into this cup were received 1760 grains of blood from the neck of a sheep. Coagulation occurred, as nearly as could be determined, in fifty-five seconds. The clot was rather dark, but became red on exposure to the air ; it was not very firm, and serum exuded from it freely. On the upper surface of the blood there was a thin separation of fibrine. The blood-corpuscles were much modified in character, being oval-shaped, rounded, and some even almost rectangular. They were reduced in number.

Into a second cup, containing four drachms of simple distilled water, 1760 grains of blood were received from the same animal. The blood coagulated at the same moment as in the previous specimen. The clot, dark at first, became red on exposure to the air, and gave out serum freely. On its upper surface there was also a thin separation of fibrine. The corpuscles were modified precisely as in the preceding observation. The normal period of coagulation of the blood of this animal was forty seconds. The clot naturally formed was of bright red colour and very firm and uniform, showing no fibrinous separation. The corpuscles were natural.

On the same day four grains of urea, with eight fluid-drachms of distilled water, in which the urea was dissolved, were placed in a cup having a capacity of 2000 grains. Into this cup I received from the neck of another sheep 1520 grains of blood. Coagulation occurred in fifty-six seconds. The clot, at first dark, became red on exposure to the air, yielded at once a large exudation of serum, and was loosely

held together. On its upper surface there was a well-marked soft fibrinous coat. The clot soon became very small, and again of deep dark colour. The corpuscles presented the peculiarities of form and scantiness noticed in the last experiments, but in a more marked degree.

Into another cup containing 480 grains of simple distilled water, were received from the neck of the same animal 1520 grains of blood. Coagulation occurred at the same time to a second, as in the preceding observation. The coagulum presented the same characteristic changes, and the corpuscles did not vary in any single particular.

The blood in this animal coagulated naturally in forty seconds. The clot was red from the first, and firm. The corpuscles were normal.

The temperature of the day on which these experiments were made was high, 70° in the shade.

Comparing these experiments one with the other, and comparing them also with another series of experiments on the addition of water to blood, to which I have already drawn the attention of the profession, the conclusion to which I am brought is, that urea in the blood, in such proportions as we consider extreme, as during uræmia in the human subject, does not, per se, produce any extra fluidity of blood; and that when it is largely diluted and added to blood, the results presented are due, exclusively, to the physical effects produced by the water.

Comparing further these experimental truths with the pathological conditions of the blood in uræmia,

we find that there is an identity of representation to an extent that is singularly remarkable.

In uræmia, uncomplicated with acute inflammatory action, the blood shows a tendency to soft gelatinous fibrinous separation; the clot produced is soft and dark, and yields abundance of water; the corpuscles are not broken, but rendered irregular and scanty. The hæmatine consequently is not effused; and, although there may be congestion of soft parts and effusions of serum, there is no true hæmorrhagic exudation.

The effects presented are due to the suppression of urinary water, and not to the urea; which, though active in its way as a poison, is not a blood-solvent.

The comparisons here instituted obtain as a general rule; and when that rule is broken, it is through a modification, either in the course of the diseased manifestation itself, or in changes occurring immediately before or after death. In other words, when in uræmia the blood is found permanently fluid and surcharged with ammonia, the fluidity, dependent on the alkaline constituent, is produced either by some unusual circumstance giving origin to an excess of alkali, or by chemical changes occurring in the urea itself, at or after death, by which its conversion into carbonate of ammonia is brought about.

We have thus, step by step, followed out the cause of uræmic coma. We have determined absolutely that the disease depends on suppression of secretion of the urine; we have analysed this secretion, and examined the various constituents; we have excluded



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