THE CLOTTING OF BLOOD. 37 



time after death, possesses the power of clotting) may be kept in the peri- 

 cardial bag as in a living cup for many hours without clotting, and yet a 

 small portion removed with a pipette clots at once. 



This relation between the blood and the vascular wall may be disturbed 

 or overridden : clotting may take place or may be induced within the living 

 bloodvessel. When the living membrane is injured, as when an artery or 

 vein is sharply ligatured, or when it is diseased, as for instance in aneurism, 

 a clot is apt to be formed at the injured or diseased spot ; and in certain 

 morbid conditions of the body clots are formed in various vascular tracts. 

 Absence of motion, which in shed blood as we have seen is unfavorable to 

 clotting, is apt within the body to lead to clotting. Thus, when an artery 

 is ligatured, the blood in the tract of the artery on the cardiac side of the 

 ligature, between the ligature and the branch last given off by the artery, 

 ceasing to share in the circulation, remains motionless or nearly so, and 

 along this tract a clot forms, firmest next to the ligature and ending near 

 where the branch is given off; this perhaps may be explained by the fact 

 that the walls of the tract suffer in their nutrition by the stagnation of the 

 blood, and that consequently the normal relation between them and the 

 contained blood is disturbed. 



That the blood within the living bloodvessels, though not actually clot- 

 ting under normal circumstances, may easily be made to clot, that the blood 

 is always on the point of clotting, is shown by the fact that a foreign body 

 such as a needle thrust into the interior of a bloodvessel or a thread drawn 

 through and left in a bloodvessel, is apt to become covered with fibrin. 

 Some influence exerted by the needle or thread, whatever may be the cha- 

 racter of that influence, is sufficient to determine a clotting, which other- 

 wise would not have taken place. 



The same instability of the blood, as regards clotting, is strikingly shown, 

 in the case of the rabbit, by the result of injecting into the bloodvessels a 

 small quantity of a solution of a peculiar proteid, prepared from certain 

 structures such as the thymus body. Massive clotting of the blood in 

 almost all the bloodvessels, small and large, takes place with great rapid- 

 ity, leading to the sudden death of the animal. In contrast to this effect 

 may be mentioned the result of injecting into the bloodvessels of a dog a 

 quantity of a solution of a body called albumose, of which we shall here- 

 after have to treat as a product of the digestion of proteid substances, to 

 the extent of 0.3 gramme per kilo of body weight. So far from producing 

 clotting, the injected albumose has such an effect on the blood that for several 

 hours after the injection shed blood will refuse to clot of itself and remain 

 quite fluid, though it can be made to clot by special treatment. 



23. All the foregoing facts tend to show that the blood as it is flow- 

 ing through the healthy bloodvessels is, as far as clotting is concerned, in a 

 state of unstable equilibrium, which may at any moment be upset, even 

 within the bloodvessels, and which is upset directly the blood is shed, 

 with clotting as a result. Our present knowledge does not permit us to 

 make an authoritative statement as to the exact nature of this equilib- 

 rium. There are reasons, however, for thinking that the white corpuscles 

 play an important part in the matter. Wherever clotting occurs natu- 

 rally, white corpuscles are present; and this is true not only of blood but 

 also of such specimens of pericardial or other serous fluids as clot natu- 

 rally. And many arguments which we cannot enter upon here, may be 

 adduced all pointing to the same conclusion, that the white corpuscles play 

 nn important part in the process of clotting. But it would lead us too far 

 into controversial matters to attempt to define what that part is, or to explain 

 the exact nature of the equilibrium of which we have spoken. 



