74 THE BODY AT WORK 



alcohol-coagulated blood could not be proteid, he termed it 

 " fibrin-ferment." He neglected the control experiment. He 

 failed to ascertain whether or not all three substances were 

 needed. Had he tried adding fibrin-ferment to fibrinogen, he 

 would have discovered that the further addition of fibrinoplastin 

 was unnecessary. He did not ascertain, as he might have done, 

 that the weight of fibrin formed is somewhat less, not greater, 

 than the weight of fibrinogen used. (Fibrinogen gives off a 

 certain quantity of globulin when it changes into fibrin.) He 

 was also wrong in supposing that the water which he added to 

 alcohol-coagulated blood dissolved no protein. His " fibrin - 

 ferment " is always associated with a protein. Since it may 

 also be obtained from lymphatic glands, thymus gland, and 

 other tissues which contain lymphocytes, it has been inferred 

 that it is itself a protein, of the class known as nucleo-proteins. 

 The fact that it is destroyed at so low a temperature as 55 C. 

 has been supposed to confirm the theory that it is a protein. 

 But with regard to the chemical nature of fibrin-ferment, as of 

 all other ferments, we are at present in the dark. Under 

 ordinary circumstances, when blood clots, the fibrin-ferment, 

 or plasmase, or thrombin it has received various names is 

 set free by leucocytes. Fluids which contain fibrinogen clot on 

 the addition of a " ferment " which is either secreted by leuco- 

 cytes or set free from leucocytes when they break up as they 

 are very apt to do, as soon as the conditions upon which their 

 health depends are interfered with. 



Freshly shed blood contains minute particles, termed " plate- 

 lets," in diameter measuring about a quarter that of a red blood- 

 corpuscle. When the inner coat of a vessel is injured, platelets 

 accumulate at the injured spot. They form a little white heap, 

 from which coagulation starts. Evidently they supply the 

 ferment, or a precursor of the ferment. As yet their origin has 

 not been traced. They are too large to be the unchanged 

 granules of granular leucocytes, but that they are in some way 

 derived from leucocytes seems probable. 



The further study of coagulation has shown that the con- 

 ditions under which it occurs are more complicated than the 

 simple explanation just given would seem to imply. This 

 explanation holds good, so far as it goes, but facts connected 

 with the details of the process have recently been brought to 



