28 THE BLOOD 



experiment as in the case of blood coagulating out of the body. Leech- 

 drawn blood remains liquid in the body of the animal ; and the blood 

 flowing from a leech-bite presents the same persistent fluidity. This 

 explains the well-known fact that this insignificant wound gives rise to 

 considerable hemorrhage. 



With the intention to simplify as much as possible the exposition of 

 the theory of coagulation and to remove sources of confusion, I shall 

 adopt in its description the theory of Schmidt as modified chiefly by 

 the researches of Hammarsten and Lilienfeld. In this theory it is as- 

 sumed that a substance is developed in coagulating blood that is capable 

 of reacting with fibrinogen to produce fibrin. By the disintegration of cer- 

 tain of the leucocytes and the blood-platelets, a nucleo-albumin is given 

 off, which unites with calcium to form thrombin. This nucleo-albumin is 

 called prothrombin. In the reaction .that results in the formation of 

 fibrin, the fibrinogen molecule is split into a body that unites with throm- 

 bin, leaving a new substance called fibrin-globulin. Sixty to ninety per 

 cent, however, of the fibrinogen molecule enters into the composition of 

 fibrin. The presence of calcium salts is necessary to the change of pro- 

 thrombin into thrombin ; but Hammarsten has succeeded in producing a 

 fibrin containing only 0.005 per cent of calcium. The agency of the 

 blood-platelets in the production of fibrin can hardly be doubted. Micro- 

 scopical observations have revealed filaments of fibrin radiating from 

 these bodies partially disintegrated. The formation of fibrin, indeed, 

 may be simply described as follows : 



Prothrombin and Thrombin. As the result of disintegration of 

 blood-platelets (Lilienfeld-) and of certain leucocytes, a nucleo-albumin 

 is formed called prothrombin ; prothrombin unites with calcium to 

 form thrombin ; finally, thrombin splits the molecule of fibrinogen, com- 

 bines with part of this molecule to form fibrin and leaves a part that is 

 called fibrin-globulin. 



Uses of Coagulation. The property of the blood under consideration 

 has an important office in the arrest of hemorrhage. The effect of ab- 

 sence of or great diminution in coagulability is exemplified in instances 

 of what is called the hernorrhagic diathesis, or hemophilia, a condition 

 in which slight wounds are followed with alarming and sometimes fatal 

 hemorrhage. This condition may exist for years and is not character- 

 ized by any peculiar symptoms except an obstinate flow of blood from 

 slight wounds. 



Hemophilia is the most striking example in medicine of transmis- 



ion by inheritance. It has been traced through successive generations 



in a single family for more than two hundred years. It affects males 



much more frequently than females, the ratio being more than ten to 



