230 FUNCTIONS OF NUTRITION. 



coagula after they are formed. In such cases the surgeon places a 

 ligature upon the wounded artery, and in this way controls the 

 hemorrhage. But the ligature is only a means of applying compres- 

 sion for a longer time, and is still temporary, as it must finally come 

 away by ulceration through the coats of the vessel. The essential ob- 

 stacle to the flow of blood in a ligatured artery is the coagulum formed 

 in the vessel behind the ligature ; which, when the ligature is detached 

 by ulceration, has become sufficiently dense and adherent to resist the 

 impulse of the blood. 



The importance of coagulation in this respect is shown by the diffi- 

 culties which follow where it is deficient. In some cases of the ligature 

 of large arteries, in patients exhausted by injury or loss of blood, when 

 the ligature comes away 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 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 

 wound, or trivial surgical operation, may be followed by long-continued 

 or fatal hemorrhage. 



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

 quantity of blood in the living body is surrounded with difficulties. 

 The earliest and simplest method adopted was by suddenly dividing 

 all the vessels of the neck in a living animal and collecting the blood 

 which escaped. But this method is 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 divided vessels, 

 and because the heart's action begins to fail before the vascular system 

 is empty. A certain quantity of blood always remains in the body after 

 death by hemorrhage ; amounting sometimes to over 25 per cent, of the 

 entire mass. The animal therefore dies before he has lost quite three- 

 fourths of the circulating fluid. 



Of the other methods which have been adopted there are none abso- 

 lutely free from possible sources of error. The best are those by 

 which, after all the blood is discharged which escapes spontaneously 

 from divided vessels, the circulatory system is injected with a weak 

 saline solution, until the fluid, after traversing the vascular channels, 

 returns colorless. The quantity of blood thus washed out is then 

 ascertained by comparing the fluid of injection with a watery dilution 

 of blood of known strength. 



The most accurate process is that employed by Steinberg,* who, after 

 bleeding the animal to death, injected the aorta with a watery solution 

 of sodium chloride, of one-half per cent., until the fluid of injection re- 

 turned colorless. The whole of it being then mingled, the hemoglobine 

 which it contained was determined as follows by the spectroscopic test : 

 Equal quantities of pure blood, in two similar test-tubes, were diluted, 



* Archiv fur die gesammte Physiologic. Bonn, 1873, Band vii., p. 101. 



