454 BLOOD AND LYMPH. 



sists of serum plus the blood corpuscles. Blood that has been 

 whipped in this way is known as "defibrinated blood." It re- 

 sembles normal blood in appearance, but is different in its com- 

 position; it cannot clot again. The physiological value of clotting 

 is that it stops hemorrhages by closing the openings of the wounded 

 blood-vessels. 



Time of Clotting. In human blood the time necessary for clot- 

 ting varies greatly, according to the conditions to which the blood 

 is subjected after shedding. Blood allowed to flow from a wound 

 into a receiving vessel may clot within a few (3 to 10) minutes 

 according to the amount of blood drawn, the extent of surface 

 with which it comes into contact, the condition of the receiving 

 vessel, etc. The same blood taken from a vein into a clean 

 syringe, by the operation of venepuncture, and emptied into a 

 perfectly clean vessel, may require from 30 to 40 minutes before it 

 jellies throughout. If the surfaces with which the shed blood 

 comes into contact are coated with oil or vaseline, clotting may be 

 delayed for even a longer time. These differences may be under- 

 stood when we remember that clotting is a complicated process 

 which involves a series of preliminary 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 

 clinical 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 



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

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

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



