quickened or delayed according as the circulatory canals are opened early, or left unopened.]

2. That in states of the body in which the blood is superfibrinised, either from active hyperinosis, or from relative increase of fibrin, there is often a modified form of coagulation, consisting of a separation of blood into three parts; viz., fibrin isolated, blood-corpuscles isolated or mixed up and held together by fibrin, and serum.

3. That in instances where life is destroyed by gradual arrest of respiration, the phenomenon of coagulation is only feebly exhibited; [and that the same law obtains in cases where death is induced by electricity, sudden exposure to intense heat or cold, the narcotics, and the alkalies.]

4. That an enfeebled movement of the blood in any part of the circulatory system is favourable to coagulation, and this especially if the respiration continue free.

5. That by throwing into the circulation a large quantity of water, the process of coagulation may be prevented. [That antimony produces a similar effect. in many cases; that the like result may follow death from certain natural causes, as from cyanosis; and that the same effect has been observed by various authors to follow deaths from poisoning by phosphorus, arsenic, and amylene; as well as deaths from cholera, yellow fever, typhus, and uræmia.

6. That the cause of imperfect coagulability of blood would appear to be due to one of two causes-to a positive deficiency in the elaboration of fibrin, or to the fact that the fibrin, being elaborated, is held in an abnormal state of solution in the liquor sanguinis.

7. That such absence or unusual fluidity of the fibrin is attended, as a general rule, with a modification, consisting possibly of a partial solution, of the red corpuscles.]

CHAPTER IV.

EXPERIMENTAL INQUIRY INTO THE PHYSICAL AGENCIES INFLUENCING THE COAGULATION OF THE BLOOD.

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"There are few, if any, physical hypotheses, which afford the only way of explaining the phenomena to which they are applied and therefore, admitting them to be perfectly consistent with all the known facts, they leave us in the same state of uncertainty in which the decypherer would find himself, if he should discover a variety of keys to the same cypher."-DUGALD STEWART.

I. EFFECTS OF TEMPERATURE.

IT has been shown in a preceding chapter that Hewson, Magendie, Scudamore, and other distinguished physiologists, have investigated very closely the effects of temperature on drawn blood; and that the results of these inquiries have been to show, that the phenomenon of coagulation is not in any way to be attributed to the loss of heat as the ancients supposed, but, on the other hand, that an increased temperature tends the more decisively and rapidly to bring about the process of coagulation. I have myself instituted a long continued and repeated series of inquiries into this question, all of which have but led to a confirmation of this foregone conclusion. Some experimenters, as it is known, have inferred that temperature has no effect on the coagulation of blood; but this is widely different from any inference, that could be deduced from my experiments; for I

have found, without exception, that a well marked difference in the period of coagulation may be produced by exposure of blood to extremes of temperature, to wit, exposure at freezing point and at 140° Fahr. Between these points, experiments on the mere process of coagulation are, in some measure, limited; since above 140° Fahr. coagulation of the albumen is imminent; while below 32°, the physical change of freezing is probable, by which change coagulation is temporarily suspended.

[Before proceeding to the details of experiments, I think it right to point out, as a guide to future inquirers, and as an indication of some of the causes of the differences which are to be met with in the history of past inquiries, certain difficulties which beset the question of the influence of temperature on the process of coagulation.

In the first place, it is necessary rigidly to observe the rule of drawing no comparative deductions regarding the effects of temperature from experiments made on the blood of different animals, inasmuch as there are constant variations in the period of coagulation according to the animal from which the blood is taken, and independently altogether of the temperature. For example, the blood of man, of the ox, and of the pig, coagulates, under the same conditions, much more slowly than the blood of lambs, and the blood of lambs more slowly than the blood of sheep. The blood of an animal that is heated by exercise coagulates more quickly than that of one that is cold or exhausted. Again, in animals of the same kind, and under the same conditions, the period of the coagulation of their blood varies, possibly from modifications in the condition of such blood itself. For

example, I have repeatedly been present in the slaughterhouse when six sheep of the same breed, and all apparently healthy, have been slaughtered one after the other. I have received blood from each victim in the same cup, in the same quantity, and in the same temperature, and have observed variations in the periods of coagulation, ranging from fifty seconds to four minutes; nor can I, indeed, recall any two cases of this kind in which there was absolute uniformity of result. To take the same point of temperature, therefore, and to draw deductions as to the effects of such temperature on the period of coagulation in the blood of different animals is, of necessity, to make a false inference.

In the second place, in exposing the blood of the same animal to different points of temperature at the same time, it is of absolute necessity so to use the thermometer as to obtain the absolute temperature of the blood itself, and not merely of the medium in which the cup containing the blood is placed. Take, for instance, two cups of blood drawn at the same moment; place them in different conditions; place one cup in water at a temperature of 60°, and the other in water at a temperature of 100°; and, if the heat of the medium only be considered, the inference, in nine cases out of ten, will be that there is no appreciable difference as regards the period of coagulation. To show, however, that this inference is incorrect, it is only necessary to remove the thermometers from the water, at the moment when the cups for containing the blood are filled, and to immerse the bulbs of the thermometers into the blood itself. It will then be proved that the mercury in the thermometer from the cold medium, as soon as the bulb is immersed in the blood, runs up quickly towards the

point of the temperature of the blood, i.e., to 90°, or a degree or two more; while the mercury which has been exposed to the higher temperature will, on the thermometer being immersed in the blood, sink down to the temperature of the blood. Thus the two bloods, although placed under such different circumstances, are in fact, within a degree or two, of the same heat; and as the period of coagulation is one sometimes of seconds, and at most of minutes, and as the blood is a fluid which yields up its caloric slowly, and absorbs caloric slowly, the effects of temperature are often too refined to become manifested at first sight. In order, therefore, to obviate the difficulties here described, it is positively necessary, in testing the effects of temperature, firstly, to employ extremes of temperature, and, secondly, to take the point of temperature from the blood itself. Any inference deduced without attention to these details is necessarily delusive.

Thirdly, the temperature of the surrounding atmosphere must be taken into account. In all animals the blood coagulates, as a general rule, more rapidly in very hot than in very cold weather; and, as one surface of the blood exposed in a cup is open to the influence of the external air, this influence has its effects, despite the temperature of the medium in which the containing cup is immersed. Blood, for instance, received in an open cup, and placed in water at a temperature of 120°, will coagulate more quickly if the external temperature is at 70°, than if it were at 35°, and vice versá; a fact which can only be proved by performing the same experiment in winter and in summer. This may seem a truism; but it requires to be stated to secure accuracy.

Lastly, in performing comparative experiments on