452 BLOOD AND LYMPH. 



which involves a series of prehminary changes or reactions in the 

 blood. These latter reactions may be accelerated or retarded 

 according to the conditions under which the blood is placed. For 

 chnical purposes various simple methods have been devised to 

 determine the clotting time with a drop or two of blood, such as 

 may be obtained by pricking the ear or the finger.* In using such 

 methods to compare normal with pathological bloods, it is necessary 

 to employ always the same method and to keep the conditions as 

 uniform as possible. Pathological conditions are known in which 

 the coagulation time of the blood is greatly prolonged. This is 

 notably the case in the class of persons known as bleeders (hemo- 

 philics), whose blood clots so slowly that even small wounds often 

 cause a fatal hemorrhage. True congenital hemophilia is trans- 

 missible by heredity, and exhibits the interesting peculiarity that, 

 as a rule, it affects only the male, but is transmitted only through 

 the female. That is to say, a man who is hemophilic does not 

 transmit the defect to his sons or his daughters, but the latter may 

 carry the defect in a latent form and transmit it actively to their 

 sons. The mortality from this condition is very high. On the 

 other hand, cases are known in which the coagulability of the 

 blood is so much augmented that spontaneous clotting occurs at 

 places within the veins or arteries (thrombosis), leading to serious 

 complications or even to death. To throw light on these cases it is 

 desirable, of course, to understand the process of clotting as fully 

 as possible. The problem has proved to be a diflficult and com- 

 plex one. 



General Statement of Problem. — The clotting of blood is such 

 a prominent phenomenon that it has attracted attention at all 

 times, and as a result numerous theories to account for it have been 

 advanced. Most of these theories have now simply an historical 

 interest. In recent years much experimental work has been done 

 upon the subject, the result of which has been to increase greatly 

 our knowledge of the process; but no complete explanation has yet 

 been reached. It is generally admitted that the essential constit- 

 uent of the clot — namely, the fibrin — is formed from the fibrinogen 

 normally present in the plasma, and that without this fibrin- 

 ogen clotting is impossible. If, for instance, blood is heated to 

 60° C, a temperature sufficient to precipitate the fibrinogen as a 

 heat coagulum, its power of clotting is lost. Clotting, therefore, is 

 essentially a process of the blood-plasma, as was shown indeed by 

 the old experimenters (Hewson). Moreover, it is also admitted 

 that the conversion of the soluble fibrinogen to the insoluble fibrin 



* For clinical methods of determining the coagulation time with a drop 

 or two of blood, reference may be made to the manuals of chnical diagnosis. 

 See Addis, "Quarterly Journal of Exp. Physiology," 1908, I, 305. 



