COAGULATION OF THE BLOOD. 267 



the flow of blood, even in a ligatured artery, is the coagulum which 

 forms within the vessel behind the ligature; and which, by the time the 

 ligature is detached by ulceration, has become sufficiently firm and adhe- 

 rent to resist the impulse of the blood. 



The importance of fibrine in this respect is shown by the difficulties 

 which follow in cases where it is deficient. In some instances of the 

 ligature of large arteries, in patients much exhausted by injury or by 

 previous loss of blood, the surgeon finds that when the ligature comes 

 awajr the bleeding begins again, no internal clot having been formed ; 

 and a second ligature, applied above the situation of the former one, is 

 again followed by secondary hemorrhage. In certain persons also there 

 appears to be a congenital deficiency of the coagulating ingredient of 

 the blood, a peculiarity sometimes observed in several members of the 

 same family ; and in these cases, any slight accidental wound, or tri- 

 vial surgical operation, may be followed by long-continued or even fatal 

 hemorrhage. 



Entire Quantity of Blood in the Body. The estimation of the whole 

 mass of the blood in the living body is surrounded with many difficul- 

 ties. The first and simplest method adopted for this purpose was by 

 suddenly dividing all the vessels of the neck in the living animal and 

 collecting all the blood which escaped. This method, however, was 

 found to be quite faulty, since the flow of blood ceases, in such an 

 experiment, not because the whole of it has been discharged, but because 

 coagula have formed about the orifices of the divided vessels and because 

 the force of the heart's action is no longer sufficient to overcome the 

 obstruction. A certain quantity of blood, therefore, always remains in 

 the body after death by hemorrhage ; and this quantity, as shown by 

 subsequent experiments, may even amount to over 25 per cent, of the 

 whole mass of blood. The animal therefore dies before he has lost quite 

 three-fourths of the circulating fluid. 



-Other methods have been adopted by various experimenters, none of 

 which are absolutely free from all possible sources of error. The best 

 is that by which, after all the blood is discharged which can be made 

 to escape spontaneously from divided vessels, the circulatory system 

 is immediately injected with water or a weak saline solution, until the 

 fluid of injection, after traversing the vascular channels, returns nearly 

 or quite colorless. The quantity of blood which it has thus washed out 

 of the vessels is then ascertained, either by a comparison of its color 

 with that of a watery dilution of blood of known strength, or by com- 

 paring the quantity of its solid ingredients with that of a similar watery 

 dilution. 



The most accurate of these processes is that employed by Steinberg, 1 

 who, after bleeding the animal to death, injected the aorta with a watery 

 solution of sodium chloride, of the strength of one-half per cent., until 

 the fluid of injection returned colorless. The whole of the fluid which 



1 Archiv fur die Gesammte Physiologic, 1873, Band vii. p. 101. 



