times its measure of normal serum, coagulation occurs, with no other difference than that which arises from the physical admixture.

Thus the theory of the fixed alkaline salts, or of normal alkalinity of serum, as the solvent agent of the fibrin of circulating blood, is definitely excluded.]

But, while this chemical hypothesis thus breaks down, its place is no better supplied by the chemical arguments that fibrin, as fibrin, does not exist in circulating blood at all. In chapter 11, page 53, this argument has been fully disposed of. Fibrin coagulates in aneurisms, on threads introduced into arteries, in vessels obstructed by ligature, in the occluded vessels of the dead body, and in the serous cavities when effused into them. It exudes as plastic lymph on the free surface of membranes; it coagulates there. How could any of these things occur if fibrin, as fibrin, did not exist in the circulating blood?

[Again, the other argument advanced by some physiologists, as Virchow, that the coagulation of fibrin is the result of contact with oxygen, is equally fallacious: inasmuch as coagulation takes place in the presence of nitrogen or other simple gas, from which oxygen is excluded, as readily as in oxygen itself; and even more readily in vacuo than under most other physical conditions.

As regards the effects of acids, we have seen that butyric acid dissolves fibrin; but as, when added to blood, it quickens coagulation, its influence as a solvent is excluded: while the formic and lactic acids, which modify the coagulating process, do not dissolve fibrin. These, therefore, may be rejected; not only for the reasons here given, but because the blood is alkaline.]

CHAPTER VI.

EXPERIMENTAL INQUIRY INTO THE CHEMICAL AGENCIES INFLUENCING THE COAGULATION OF THE BLOOD

(CONTINUED).

"No more causes of things ought to be admitted, but such as are both true and sufficient to explain the phenomena." SIR ISAAC NEWTON.

EVOLUTION OF GASEOUS MATTERS FROM BLOOD.

[IN our preceding inquiries, physical and chemical, we have been led irresistibly to the conclusion, that motion is not sufficient to account for fluidity, nor rest for coagulation; we have seen that exposure to the air is not alone sufficient to account for coagulation, though it is a favouring circumstance; and that mere confinement from air will not of itself sustain fluidity. We have seen that contact with living tissues is not alone competent to account for fluidity; for, while coagulation occurs in the presence of a living tissue, we have also seen fluidity sustained under certain conditions in contact with inorganic materials. We have seen that temperature is not sufficient of itself to account either for fluidity on the one hand, or coagulation on the other; inasmuch as the normal temperature of the body favours the coagulation of drawn blood, and is yet combined in the body with the circulating fluid blood. We

have seen, in regard to the effects of chemical agents, that while fibrin is evidently held fluid by some chemical principle, it is most clear that this cannot be one of the fixed substances; or it would continue to sustain the fluidity of blood, whether within or without the body.

We are thus driven, by the purest steps of exclusive reasoning, to the investigation of a new point;—namely, Is the coagulation of blood dependent on the evolution of some volatile substance, under circumstances favourable to its extrication?]

The idea that the evolution of a gaseous product from the blood is the cause of coagulation, was indeed put forward, as has already been stated, by Sir Charles Scudamore and Polli, who supposed, also, that it was to the escape of carbonic acid that the process gas of coagulation is mainly due. Scudamore did not, however, prove this position, but the contrary; for he found that carbonic acid, passed through blood, had no marked effect in retarding coagulation. This important fact, however, both of them did prove: that coagulation proceeds in proportion as carbonic acid and other gases are given off-the most important observation that had been made on the subject since Hewson's remark regarding the effects of exposure to the atmosphere.

On looking back to all that had been done, and to my own investigations, the conviction became more and more powerful that, in principle, Scudamore and Polli were right respecting the escape of some volatile substance, however wrong they might be in detail. In this direction, indeed, all evidence points, as a reference to chapter IV will prove.

[In this chapter, as the details of physical experiments advanced step by step, this view of the evolution

of gaseous matter advanced also so steadily and convincingly, as to become, by mere accumulation of circumstantial evidence, as near to demonstration as such evidence could bring it. Let us follow this chapter step by step, and examine to what it leads.

Temperature, above the standard of the body, quickens coagulation; cold retards it, and, carried to an extreme, altogether prevents it. Water at ordinary temperature added to blood, in proportion above the amount of blood used, retards coagulation, as though by retaining the volatile principle in solution for a longer time. Fluids of greater densities added to blood have the same effect. The vacuum quickens coagulation; the more intensely as the vacuum is more perfect. The same quantity of blood exposed to air over a wide surface, whether in thin stream or in extensive layer, coagulates more quickly than if retained in mass in a small space. Blood occluded from air in the vessel of an animal, or in organic tubes under cold and pressure, is prevented from coagulating. Blood in motion in a closed circuit, or in a vessel, has its coagulation retarded, while by agitation in the open air its coagulation is quickened.

These facts lend irresistible evidence to the truth of the theory now before us for consideration.]

But, even with these strong arguments in its favour, the theory is far from being proved. Every effect which has been noticed might, after all, be only a coincidence. To test the truth of the theory, therefore, became a plain and necessary duty.

In commencing an inquiry in this direction, I felt that it would be most rational and business-like, not at once to examine the nature of the substances thrown off in vapour by coagulating blood, but to ascertain

primarily whether that vapour itself had any influence. The result is given in the succeeding narrative.

Transmission of Blood- Vapour through Blood. I fitted up a simple apparatus as follows. A Wolf's bottle (A) capable of holding three pounds of fluid blood, was fitted with three good corks, so as to make it quite airtight. A bent tube (c) was fitted into one of the corks, so as to descend nearly to the bottom of the bottle by one end, and to be inserted by the other in a smaller bottle (D) placed near the Wolf's bottle. From the other side-opening passed also a glass tube, which

merely dipped into the neck of the Wolf's bottle, and bent over so as to pass to the bottom of another small bottle (F), of the same size and shape as that already mentioned. The two small bottles were also securely corked; but, in addition to the tubes already named as passing to them from the Wolf's bottle, two other tubes (H and 1) emerged from them. When the apparatus was fitted up, it was easy, by means of a small pair of