EFFECTS OF TRANSFUSION. 77 



through the vessels, that one is absolutely unable to recognise an 

 individual corpuscle in the capillaries." 1 More than half an hour 

 elapses before the velocity commences to slacken. No such increase of 

 velocity is to be observed on the injection of blood ; that is to say, after 

 the injection has ceased and the blood pressure has returned to normal. 



After the injection of blood, Worm Miiller found that during the 

 next few hours a very considerable portion of the injected plasma 

 passed out of the vessels. The surplus corpuscles disappeared in the 

 course of a few days. 



The functional power of the vascular system is lowered by pro- 

 nounced plethora. Venesection of a dog, in which artificial plethora has 

 been produced, causes the arterial pressure to fall so rapidly, that it is 

 impossible to obtain even the quantity of blood originally transfused. 

 When the injection of fluid into a vein is maintained for some time, the 

 heart must be strained by the increased diastolic pressure. It is 

 probably owing to cardiac failure that animals sometimes die during 

 continuous injections of large quantities of fluid. The collapse of 

 the heart may sometimes be prevented by the letting of blood. 2 The 

 heart has not only to do extra work when the diastolic pressure is 

 raised, but the emptying of the coronary veins is impeded, and thus the 

 coronary circulation impaired. The fact that asphyxia produces no 

 rise of arterial pressure in plethoric dogs, with the fact that they are 

 easily killed by haemorrhage, shows that there is general vasomotor 

 paralysis produced by over-distension of the vascular system. The addition 

 of blood to the extent of 150 per cent, of the normal blood quantum 

 is the outside limit beyond which life is directly threatened. 



The Pressure in the Arteries. 



The lateral pressure of the blood in the large arteries was first 

 accurately measured by Stephen Hales. 3 He writes — 



"In December 1733, I caused a mare to be tied down alive on her 

 back ; she was fourteen hands high, and about 1 4 years of age, had a 

 fistula on her withers, was neither very lean, nor yet lusty. Having laid 

 open the left crural artery about 3 in. from her belly, I inserted into it a 

 brass pipe whose bore was one-sixth of an inch in diameter ; and to that, by 

 means of another brass pipe, which was fitly adapted to it, I fixed a glass tube 

 of nearly the same diameter, which was 9 ft. in length ; then untying tbe 

 ligature on the artery, the blood rose in the tube 8 ft. 3 in. perpendicular 

 above the level of the left ventricle of the heart. When it was at its full 

 height it would rise and fall at and after each pulse 2, 3, or 4 in. ; and some- 

 times it would fall 12 or 14 in., and have there for a time the same vibra- 

 tions up and down, at and after each pulse, as it had when it was at its full 

 height, to which it would rise again after forty or fifty pulses." 



Hales drew the correct inference from his experiments that "the 

 real force of the blood in the arteries depends on the proportion which 

 the quantity of blood thrown out of the left ventricle in a given time 

 1 tears to the quantity which can pass through the capillary arteries into 

 the veins at that time." 



Simple as these experiments are, they afford us the most striking 



1 Cohnheim, he. cit., p. 457. 



2 Johansson and Tigerstedt, Skandin. Arch. f. Physiol., Leipzig, 1889, Bd. i. S. 394. 



3 "Statical Essays," vol. ii. 



