BLOOD. 485 



tion of acidified blood with ammonia, or through the prolonged action of 

 ozone, the coagulabilit}' of the blood may be completely removed. 



The intravenous injection of 0.3 gramme peptone in 0.5 per cent, salt 

 solution for each kilo of body weight in the dog likewise prevents the 

 coagulation of the blood. 



Warming of the blood above its normal temperature accelerates co- 

 agulation : so, also, the more extensive the contact of the blood with 

 foreign bodies and with the atmosphere, the more rapid the coagulation. 



If blood, as it escapes from a blood-vessel, is stirred or whipped 

 with glass rods or twigs, coagulation occurs somewhat more rapidly 

 than normally ; but instead of the entire blood being transformed into a 

 jelh', the substance fibrin on whose solidification blood coagulation 

 depends separates in the form of fibrous lumps and shreds adhering to 

 the body with which the blood is whipped. The blood is then said to be 

 defibrinated, and the fluid in which the corpuscles remain suspended is 

 termed serum, instead of plasma. Plasma is, consequent!}-, the fluid 

 constituent of blood which still contains uncoagulated fibrin elements ; 

 serum is plasma minus the fibrin elements. Serum may be obtained as 

 a clear fluid by allowing the corpuscles to settle or by separating them 

 with the centrifugal machine ; or, as already stated, it exudes from the 

 clot when blood is allowed spontaneously to coagulate. 



The coagulation of the blood consists in the formation of fibrin, an 

 albuminous body which results from the action of a ferment-like body 

 on the albuminous constituents of the plasma, the process being similar 

 to the spontaneous conversion of soluble into coagulated casein in milk 

 from the action of the casein ferment. 



The theory as to the formation of fibrin which has met with most 

 general acceptance, though we shall find that it requires some slight 

 modification, is that coagulation results when two albuminous bodies 

 contained in blood-plasma, the fibrinogen and fibrino-plastic substances, 

 unite under the influence of the fibrin ferment. The conditions governing 

 this chemical process may be made clear by the following experimental 

 facts (Foster): 



If the blood, as it flows from a divided vessel, is received in a beaker 

 containing about one-third the volume of blood of a saturated solution 

 of a neutral salt, such as magnesium sulphate, coagulation will be 

 prevented, the corpuscles will settle in time to the bottom of the vessel, 

 the fluid plasma mixed, of course, with the salt solution forming a 

 transparent la\^er above them. If some of this plasma be drawn off 

 with a pipette and diluted with eight or ten times its bulk of water, 

 coagulation will be produced. The neutral salt has, therefore, merely 

 prevented coagulation by its presence, and has not destroyed the sub- 

 stance or substances from which fibrin is formed. If to some of the 



