CHAP, i.] BLOOD. 29 



of clotting, is shewn by the fact that a foreign body, such as a 

 needle thrust into the interior of a blood vessel or a thread drawn 

 through and leh in a blood vessel, is apt to become covered with 

 fibrin. Some influence exerted by the needle or thread, whatever- 

 may be the character of that influence, is sufficient to determine" ar 

 clotting, which otherwise would not have taken place. 



The same instability of the blood as regards clotting is strikingly 

 shewn, in the case of the rabbit at least, by the result of injecting 

 into the blood vessels 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 blood vessels, small 

 and large, takes place with great rapidity, leading to the sudden 

 death of the animal. In contrast to this effect may be mentioned 

 the result of injecting into the blood vessels of a dog a quantity 

 of a solution of a body called albumose, of which we shall hereafter 

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

 to the extent of '3 grm. 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 shew that the blood as it 

 is flowing through the healthy blood vessels is, so far as clotting is 

 concerned, in a state of unstable equilibrium, which may at any 

 moment be upset, even within the blood vessels, 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 equilibrium. There are reasons how- 

 ever for thinking that the white corpuscles play an important part 

 in the matter. Wherever clotting occurs naturally, 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 naturally. 

 When horse's blood is kept fluid by being retained within the 

 jugular vein, as mentioned a little while back, and the vein is 

 hung upright, the corpuscles both red and white sink, leaving 

 an upper layer of plasma almost free from corpuscles. This upper 

 layer will be found to have lost largely its power of clotting spon- 

 taneously, though the power is at once regained if the white 

 corpuscles from the layers beneath be returned to it. And many 

 other arguments, which we cannot enter upon here, may be adduced 

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

 an 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, or to discuss such questions as Whether the 

 ordinary white corpuscles, or corpuscles of a special kind are con- 

 cerned in the matter ? Whether the corpuscles, when clotting takes 

 place, give out something, e.g. fibrinogen or ferment or both or 



