REVIEW V.

The Cause of the Coagulation of the Blood; being the Astley Cooper Prize Essay for 1856, with Additional Observations and Experiments; and with an Appendix showing the bearings of the subject on Practical Medicine and Pathology. By BENJAMIN WARD RICHARDSON, M.D., Physician to the Royal Infirmary for Diseases of the Chest, Lecturer on Physiology and on Hygienic Medicine at the Grosvenor-place School of Medicine, &c. &c.London, 1858. 8vo, pp. 466. With Three Coloured Lithographs and numerous Wood Engravings.

AMONG the admirable memoirs which have been honoured by the award of the Astley Cooper Prize,-and we doubt whether the offer of any Prize has ever given the incitement to a more valuable series of investigations,-a very high place must certainly be assigned to Dr. Richardson's Essay, looking simply to the amount and excellence of the work which it represents. But when we take into account that this work has had far more than an ordinary measure of success, having issued in a discovery of a most important character, about which it does not seem to us that any reasonable doubt can be entertained among those who carefully examine the evidence (the good faith of the author's statements as to facts being of course presupposed), we may congratulate Dr. Richardson on having produced that one among the Essays yet rewarded by the Astley Cooper Prize, which will be longest referred to as making a definite advance in Physiology, and therefore as possessing the highest scientific merit.

In saying this, however, we would not be understood as endorsing the affirmation of the author, that he has discovered "the Cause of the Coagulation of the Blood." That cause, as we shall show in the sequel, is far more recondite than he seems to suppose. But we believe him to have succeeded in bringing to light an immediate and necessary antecedent of this phenomenon, which was previously unsuspected; and to have made clear the physical and chemical conditions under which occurs that spontaneous passage of fibrin from the liquid to the solid condition, which, as our readers well know, constitutes the essential feature in the coagulation of the blood.

In presenting our readers with a critical summary of Dr. Richardson's inquiries, we think it better to follow pretty closely the path which he has himself marked out; passing by, however, for obvious reasons, the résumé of the inquiries and opinions of others which he gives at the commencement of his volume. Every point of importance which had been clearly established by Dr. Richardson's predecessors, will present itself in its proper place in our account of his researches. Several of them had been led to the idea that the immediate condition of the coagulation of blood consists in the evolution of some volatile principle; in support of which idea there may be urged a variety of considerations well known to physiologists, the chief of which are the following:

It is a well-established fact that coagulation is retarded by a reduction of temperature, and that it may be altogether prevented for a time (as John Hunter, we believe, was the first to show) by freezing the blood, which yet coagulates when thawed and exposed to an atmosphere of ordinary warmth. Conversely, the process is quickened by an elevation of temperature, above the natural standard, towards the point at which albumen coagulates. And thus if, of two samples of blood taken at the same time from the same animal, one be warmed and the other cooled, there will be a marked difference in their periods of coagulation, the interval depending upon the amount of difference of their respective temperatures. Again, it has been conclusively shown that the more freely blood is exposed to air, the more rapidly does it coagulate; so that the clot is formed more speedily

when the blood is drawn into a wide shallow vessel, than when it is received into a narrow deep one. Coagulation is also quickened by diminution of the pressure of the air, taking place most rapidly in a vacuum. Conversely, coagulation is retarded, sometimes for a lengthened period, by exclusion of the blood from the air, whether in the blood-vessels of the animal body, or in an inorganic receptacle; and, as Dr. Richardson has shown for the first time, the retardation may be sustained ad libitum by adding pressure to exclusion. Thus, having laid bare the external jugular of a cat, and placed an inch of it between two ligatures, he removed the ligatured part, and immersed it in mercury beneath the pressure of a column about thirty inches high. After having been left there for twenty hours, the piece of vein was withdrawn, placed in a spoon, and punctured; its contained blood flowed out entirely fluid, and on its exposure to the air coagulated in four minutes. Some blood of this same animal, derived from the jugular vein at the time of operation, coagulated on exposure to the air in two minutes and a half.

Further, coagulation is materially retarded by the admixture of blood with fluids at or above its own density, and also by addition of water in excess; the addition of water to blood, however, in the proportion of equal parts of each liquid, does not materially influence the period of coagulation, unless the temperature of the water added be raised to that of the blood, in which case the coagulation is accelerated.

Lastly, agitation of blood that is freely exposed to the air, has a very decided influence in quickening coagulation. Yet motion per se has no such influence; for if the blood be shut up in a closed vessel, motion rather retards than accelerates its coagulation. Dr. Richardson has devised an ingenious apparatus for imitating the natural circulation in some degree, by keeping the blood in movement within a circuit of tubes composed of inorganic materials, and closed as completely as possible; and he has found that blood may be kept in motion in such a circuit for a brief period without coagulating, but that ultimately the fibrin is deposited on the expanded parts of the circuit.

The foregoing conditions, as our author justly observes, are all in perfect accord with the hypothesis that coagulation is immediately dependent on the escape of a volatile agent from the blood; whilst, in the presence of any other view, these phenomena are not merely disjointed, but even appear contradictory. With a view of putting this hypothesis to the test, Dr. Richardson devised the following ingenious experiment. A large Woolf's bottle was connected by bent tubes with two small bottles; the apparatus being so arranged that a stream of air from a small pair of bellows should first pass through an ounce of blood in one of the small bottles, then through two pounds of blood in the large bottle, and lastly, through another ounce of blood in the second small bottle. The three bottles having been charged with blood obtained at one gush from the throat of an ox, the difference in the rate of coagulation of their contents was very striking. The blood through which air was first passed coagulated in two minutes; that in the large bottle coagulated in three minutes; whilst the blood in the third bottle, which received the vapour from the whole mass of the contents of the second, retained its colour and its full fluidity for eight minutes and a half. In another experiment of the same kind, it was observed that the lower stratum of blood in the third bottle coagulated rapidly and became dark, while all above remained of a bright colour and fluid; and it was found on examination that the tube which conducted the blood-vapour from the large bottle was not pushed down far enough, so that the lower stratum of blood was not subjected to its influence.

That the volatile agent on the escape of which the coagulation of the fibrin immediately depends, is Ammonia, seems to have been suggested to Dr. Richardson by the well-known power which the fixed alkalies possess of keeping fibrin in solution. On this point he has made a large number of experiments; and he has shown that the discrepancy of the results obtained by others is probably to be attributed to a want of purity in the reagents employed, as in the following striking example:

"Being anxious to ascertain the effect of nitrate of potass on freshly extracted fibrin, I obtained two specimens of this salt from two different chemical establishments. Both specimens were warranted as carefully prepared. With each of these specimens I made a solution in the proportion of ten grains of the salt to one ounce of distilled water. Into each solution I dropped two grains of moist fibrin, derived from the same blood, and left them standing side by side under the same conditions. In three days, I found that the fibrin in one of the solutions was in a great measure dissolved; in the other it remained unchanged. This difference arose from the fact that the salt which had dissolved the fibrin contained free potassa; the other salt did not." (p. 50.)

1;

Dr. Richardson states, as the result of his experiments on this point, that for holding blood permanently fluid, the proportion of either of the fixed alkalies must not be less than one grain to the fluid ounce, or one part in five hundred and five by weight; and that no normal blood-salt has the power of effecting the solution of fibrin, nor yet of holding blood fluid, except when added in proportions which would be incompatible with life if introduced into the circulation. Hence it becomes obvious that as the fluidity of the blood in the vessels cannot be attributed to the presence of the fixed alkalies, since these are equally present in blood which is undergoing coagulation, if the presence of an alkali has any concern with it, this must be the volatile alkali, ammonia: and under the guidance of this clue, Dr. Richardson has made a large number of experiments, to determine, in the first place, whether ammonia is given off from blood during its coagulation; secondly, whether by the retention of ammonia in the blood its fluidity may be preserved and thirdly, whether a coagulum of fibrin already formed can be redissolved by the addition of ammonia, to be re-formed when the ammonia is allowed to escape. That ammonia is evolved from blood on its being withdrawn from the vessels and exposed to the air, has been proved most satisfactorily by Dr. Richardson's experiments, which have been so multiplied and varied as to exclude all sources of fallacy. The test is a very simple one; being the formation of minute crystals of chloride of ammonium on a slip of glass previously moistened with hydrochloric acid and exposed to blood-vapour. For the precautions which must be taken in order that this test may be applied with a satisfactory result, we must refer to Dr. Richardson's own pages. It is worthy of being specially noticed, that the evolution of ammonia does not cease with the act of coagulation, unless the clot be exposed to a temperature at or below 32° Fahr., when all gaseous evolution ceases, and also the further act of separation into clot and serum. If, on the other hand, a recently formed clot be divided into small pieces, and be placed in a vessel surrounded with water at 100° Fahr., there is a rapid separation of serum and a continued evolution of vapour; the subsequent contraction of the clot being but an extension of the first act of coagulation. Thus, then, the fact of the evolution of ammonia from freshly-drawn blood is incontestably established; but the quantity evolved is extremely minute; and this phenomenon, like the evolution of carbonic acid, might reasonably be regarded as a mere coincidence, if its special relation to the act of coagulation could not be proved in any other way.

It appears, however, from Dr. Richardson's next series of experiments, that the introduction of a small quantity of ammonia into blood whilst yet liquid, has the effect of retarding its coagulation for a period proportional to the amount; and that the like effect is produced by the transmission of air charged with ammoniavapour through blood. Thus, when four one-thousand-grain bottles, into which respectively one grain, one-half grain, one third-grain, and one-fourth grain of ammonia had been previously introduced, were filled with blood drawn from the same animal, the blood in the first was fluid three hours afterwards, that in the second coagulated feebly at the end of thirty-five minutes, that in the third remained fluid for twelve minutes and then coagulated, whilst that in the fourth coagulated in three minutes; another sample of the same blood coagulated firmly in one minute on simple exposure to air at sixty degrees Fahr. By means of an apparatus specially contrived for the purpose, Dr. Richardson drove air charged with three grains of ammonia-vapour through five hundred grains of blood: the

blood remained fluid during the twelve minutes that this process lasted. Half the blood being then set aside in an evaporating dish at rest, half an hour was required for its coagulation; through the other half a current of air was driven, and it coagulated in three minutes. The blood of the animal used in this experiment coagulated naturally in four minutes at a temperature of fifty degrees. The solvent effect of ammonia upon fibrin had been observed by Dr. Richardson some years previously, in the course of some inquiries which he made with a view to determine the most likely means of preventing the formation of fibrinous concretions in the heart during life. Ten-grain masses of moist fibrin being placed in solutions of ammonia of the respective strengths of five grains, two and a-half grains, and two grains, to one thousand grains of water, their solution was accomplished in fifteen, seventeen, and twenty-one days respectively. In another experiment, a similar quantity of fibrin was divided into small pieces, which were placed in a mixture of twenty minims of strong liquor ammonia with two ounces of water: the fibrin soon began to gelatinize, and in five days had entirely disappeared, forming a sticky solution, which evolved ammonia freely. This solution was kept by Dr. Richardson nearly four years, closed up in its bottle, during which time it seemed to undergo no change. It does not seem to have occurred to him, however, to try whether, on freely exposing it to the air so as to allow the ammonia to escape, its redissolved fibrin would again coagulate.

That after the solvent action of ammonia has been exerted on the coagulum of blood, so that fluidity has been completely restored, a recoagulation will take place when the escape of ammonia is permitted, is the result of another series of Dr. Richardson's experiments; the conditions of which were so varied as to justify his statement that "in blood held temporarily fluid by excess of ammonia, coagulation is favoured or retarded by the same physical agents as those which favour the normal coagulation of blood."

The conclusion drawn by Dr. Richardson from the series of facts of which the foregoing are samples-namely, that the fibrin of the circulating blood is held in solution by ammonia, and that on the escape of this volatile solvent from newlydrawn and liberated blood the passage of the fibrin from the fluid to the solid condition immediately depends,-seems to us to be entitled to take rank as a well-supported theory, if not to be at once admitted as a demonstrated doctrine. We are not inclined to attach much weight to the objection which we have heard raised against it, that the liberation of ammonia from the whole mass of coagulating blood could scarcely take place in so brief a period; for it is well known that ammonia may be transmitted through aqueous liquids with extraordinary rapidity; and (as already shown) although the escape of ammonia commences almost immediately that the blood is drawn, it really continues for some time afterwards. The objection seems early to have occurred to Dr. Richardson himself; and he remarks that his doubt was dispelled by the constancy of the relation between the rapidity of the evolution of ammonia, and the rapidity of coagulation. Thus in sheep's blood which coagulates rapidly, the indication of its liberation afforded by the formation of crystals is as marked in one minute, as it is in the case of the blood of the ox, which coagulates slowly, after three or four minutes. And the chemical condition of rapid evolution seems to be supplied by the fact, that the blood is rendered feebly alkaline by the presence of a quantity of fixed alkali or alkaline carbonate, which is not sufficient to hold the fibrin in solution, but serves to expel the ammonia (especially with the aid of gentle warmth) when the blood is exposed to air or to a vacuum. Dr. Richardson has endeavoured to ascertain by experiment the proportion of ammonia which will be required to maintain the fluidity of circulating blood; and he has come to the approximate conclusion that the maximum would be one part of the alkali to sixteen of fibrin, or one part of the alkali to eight thousand of blood containing two per cent. of fibrin. The proportion, he remarks, may be less, but need not be more. Considering how very imperfectly the natural condition of the circulating blood can be imitated by any artificial arrangements, we are inclined to think that the actual proportion

of ammonia in the blood of the living body is considerably below this esti

mate.

It is an important corroborative fact, as indicating the normal presence of free ammonia in the circulating blood, that the volatile alkali is ordinarily given off in the act of expiration. This was first noticed about fifteen years ago, by the Rev. J. B. Reade; who detected microscopic crystals of chloride of ammonium on a slip of glass, previously moistened with hydrochloric acid, which had been exposed to the expiratory blast. MM. Viale and Latini, in 1854, arrived at the same conclusion, by a series of independent labours; and Dr. Reuling published a paper in the same year, in which he affirms that ammonia is contained in the expired breath of every one, though ordinarily to no greater amount than in the atmosphere, but that it is in large excess in the breath of patients suffering under typhus, pyæmia, and uræmia. Dr. Richardson states that he has made upwards of a thousand experiments on this point, on animals of various kinds, as well as on human beings of both sexes, and under varying conditions as regards temperature of body, time of day, repose and fatigue, health and disease. He has found the test of the formation of microscopic crystals more satisfactory than any other; and he applies it by means of the following simple apparatus:-A slip of glass

A

is secured by india-rubber bands across the trumpet-shaped orifice (A) of a straight breast pump, into the bulb of which (B) a drop or two of pure hydrochloric acid has been introduced; the subject of the experiment being made to expire through the small end of the tube, the air passes through the acid vapour, and whilst part of the alkali is fixed in the bulb, another portion goes on to be condensed on the slip of glass. Dr. Richardson has found the exhalation of ammonia to be the general fact, though not without exception; and he has proved that the alkali is really thrown off from the body, and not merely returned from the air inspired by testing the air which was being breathed, driving it through the same apparatus for a time equal to that consumed in the respiratory acts, without the formation of any crystals of chloride of ammonium. The most marked and constant exception presented itself in the case of a gentleman who lived entirely on vegetable food and abstained from alcoholic drinks; no trace of ammonia being detectable under any circumstances in his breath. But Dr. Richardson states that he sometimes found his own breath free from it on rising in the morning after a sound night's rest, and that the quantity was very much reduced in cold weather; whilst, conversely, a state of fatigue and a high temperature are accompanied by an augmented evolution. In a case of simple anæmia, he could not obtain the slightest evidence of the presence of ammonia; whilst an excess presented itself in a considerable variety of other diseases. It has been found by Mr. Blake that when ammonia is artificially introduced into the blood, it is so rapidly removed by pulmonary exhalation, that a rod dipped in hydrochloric acid gives white fumes when held in the respiratory current a few seconds afterwards. The evolution of ammonia in the cutaneous exhalation has long been known; and the suddenness with which it sometimes takes place, especially in females, under mental emotion, is an evidence both of the large amount which must be present in the blood, and of the rapidity with which, under conditions not yet known, it may be set free. Dr. Richardson states that the cutaneous evolution is so marked during and after the colliquative sweats of consumptive patients, that he has