7 6 



THE MECHANISM OF THE CIRCULATION. 



thus neither the arterial nor the venous pressure can be driven up 

 beyond a certain point ; and this point, it is noticeable, is not very far 

 removed from the normal pressure. After the transfusion of large 

 quantities of fluid, both the venous and arterial pressures return rapidly 

 to normal. On injecting a volume of fluid equal to that of the blood, 

 Grosglik 1 estimated that 69 to 79 per cent, transuded in the first 

 hour. On injecting saline coloured with methyl blue into the circulation, 

 the blue colour appears in five to ten minutes in the stomach and the 

 bladder. Dastre and Loye 2 found that, on injecting saline at the rate of 

 1 c.c. per minute for each kilo, of body weight in the dog, the transfusion 

 was compensated by an equally rapid excretion from the kidney. 



In the diagram (Fig. 49) is exhibited the effect on the arterial, 

 portal, and vena cava pressures produced by the injection of 500 c.c. of 

 normal saline solution ; an amount fully equal to the blood quantum of 

 the dog. It will be seen that five minutes after the injection was 

 finished, the vena cava pressure had risen only 60 mm. MgS0 4 solution, or 

 scarcely 5 mm. Hg. In another experiment, 350 c.c. of normal saline were 



Fig. 49. — Effect of injection of 500 c.c. saline solution on the arterial pressure 

 (black line), portal pressure (fine line), and vena cava pressure (interrupted line). 

 — Bayliss and Starling. 



injected during the space of two and a half minutes into a dog. During 

 the injection the arterial pressure rose from 60 to 70 mm. Hg, the portal 

 pressure from 87 to 167, and the vena cava pressure from 34 to 124 

 mm. MgS0 4 solution. Ten minutes later the pressures had become 

 — arterial 72 mm. Hg, portal 110 mm., and vena cava 50 mm. 

 MgS0 4 solution. 3 After the injection of saline the velocity of the blood 

 stream is very considerably accelerated, not merely during the injection, 

 and simultaneously with the rise of blood pressure, but also lastingly, 

 long after the pressure has again become normal. The cause of this is the 

 lessening of the viscosity of the blood by dilution. The increase of velocity can 

 be observed in the frog's web after injection of 1 c.c. of normal saline into 

 the vena abdoininalis, " the light-coloured blood shoots with such rapidity 



1 Arch, dc physiol. norm, et path., Paris, 1890, p. 704. 



2 Ibid., 1888, p. 93 ; 1889, p. 253. 



3 Bayliss and Starling, Journ. Physiol., Cambridge and London, 1894, vol. xvi. p. 128. 



