USES OF COAGULATION 29 



one. It is a curious fact that the diathesis comes through the females, 

 who are not themselves "bleeders." The daughters transmit it to their 

 sons, but male bleeders seldom transmit the diathesis except to 

 daughters, whose sons usually are bleeders. It has also been observed 

 that the females in bleeder-families are very prolific. Hemophilia may 

 develop spontaneously, without heredity, but it nearly always is 

 congenital. 



During coagulation, fibrin assumes a filamentous form, presenting, 

 under the microscope, the appearance of rectilinear fibrillae. These 

 fibrillae gradually increase in number, and as contraction of the clot 

 occurs, they become irregularly crossed. They are always straight, 

 however, and never assume the wavy appearance characteristic of true 

 fibrous tissue. 



The blood of the renal and hepatic veins, capillary blood, and the 

 blood which passes from the capillary system into the veins after death 

 usually does not coagulate or coagulates very imperfectly ; in other 

 words, blood from these parts does not readily form fibrin. The reason 

 of this peculiarity is not known ; but the fact affords a partial explanation 

 of the normal fluidity of the blood ; for this liquid, passing over the 

 entire course of the circulation in about thirty seconds, seems to be los- 

 ing its coagulability in its passage through the liver, kidneys, and the 

 general capillary system as fast as its coagulability is increased in the 

 other parts. Taking into consideration the rapidity of the circulation, 

 it is evident that coagulation can not take place while the normal circu- 

 lation is maintained and while the blood is undergoing the changes 

 incident to general metabolism. 



