THE BLOOD. 55 



blooded animals is prevented by the injection of an effusion of the 

 mouth of the officinal leech into the blood-current (HAYCRAFT). 

 If the blood-circulation of a dog is cut off between the liver and 

 intestines and the blood allowed to flow only through the head and 

 the viscera of the thoracic cavity, the coagulation of the blood is 

 destroyed (PAWLOW, BOHR). If we alloM the blood to flow 

 directly, while we stir it, into a neutral salt solution best a satu- 

 rated magnesium sulphate solution (1 vol. salt solution and 3 

 vols. blood) we obtain a mixture of blood and salt which re- 

 mains uncoagulated for several days. The blood-corpuscles which, 

 because of their adhesiveness and elasticity, would otherwise pass 

 easily through the pores of the filter-paper are made solid and stiff 

 by the salt, so that they may be easily filtered. The plasma thus 

 obtained, which does not coagulate spontaneously, is called " salt- 

 plasma" 



On coagulation there separates in the previously fluid blood an 

 insoluble or a very difficultly-soluble albuminous substance, fibrin. 

 When this separation takes place without stirring the blood coagu- 

 lates to a solid mass which, when carefully severed from the sides 

 of the vessel, contracts, and a clear, generally yellow-colored liquid, 

 the Uood-serum, exudes. The solid coagulum which incloses the 

 blood-corpuscles is called the blood-clot (placenta sanguinis). If 

 the blood is beaten during coagulation, the fibrin separates in 

 elastic threads or fibrous masses, and the defibrinated blood which 

 separates is sometimes called cruor, 1 and consists of blood-cor- 

 puscles and blood-serum. 



The defibrinated blood consists of blood-corpuscles and serum, 

 while the uncoagulated blood consists of blood-corpuscles and 

 blood-plasma. The essential chemical difference between blood- 

 serum and blood-plasma is that the blood-serum does not contain 

 the mother-substance of fibrin, the fibrinogen, which exists in the 

 blood-plasma, and the serum is proportionally richer in another 

 body, the fibrin ferment (see page 58). 



1 The name CRUOR is used in different senses. We sometimes understand 

 thereby only the blood when coagulated to a red solid mass, in other cases 

 the blood-clot after the separation of the serum, and lastly the sediment con- 

 sisting of red blood-corpuscles which is obtained from defibrinated blood by 

 means of centrifugal force or by letting it stand. 



