166 THE VASCULAR SYSTEM 



in the venae cavee rises during each injection but sinks again owing 

 to the extensibility and large potential capacity of the capillary- 

 venous system. The liver holds a great deal and becomes large 

 and firm to the touch, and when excised a great quantity of blood 

 streams from it. The large abdominal veins and liver by receiving 

 most of the blood injected protect the heart from over-distension, 

 but if the transfusion into the jugular vein be made too rapidly, 

 no time is given for the filling out of the liver and other capillary- 

 venous reservoirs, and the heart becomes over-loaded and fails. 



Plethysmographic records of the heart showed Johansson and 

 Tigerstedt that with a sufficiently slow transfusion there is an 

 increase in the systolic output and no passive congestion of the 

 heart occurs. With a more rapid rate of transfusion the heart 

 fails to empty itself and expels a smaller amount of blood than 

 before. Hence the constancy of the arterial pressure during 

 transfusion is to be ascribed largely to the heart's action. 



Rabbit : period of transfusion of 30 per cent, of blood 

 quantum marked by the vertical lines : 



Output measured by Stromuhr introduced into Ascending Aorta 



Arterial pressure . 78 

 Output of heart per 18 



88 99 97 114 131 134 133 140 

 32 53 39 31 33 32 38 36 



minute per kgm. 

 of body weight 



144 147 148 146 148 147 148 149 147 

 36 36 38 36 32 44 45 51 60 



146 131 119 112 107 104 101 99 94 90 

 66 66 66 61 59 59 59 54 50 51 



The following shows the effect of a larger rapid injection = 

 50 per cent, of the blood quantum : 



Arterial pressure . 78 

 Minute volume 33 



89 120 130 144 158 160 

 49 80 71 51 35 32 



151 146 136 

 31 32 33 



131 122 



and so on to -55- and then to -^ , the output rising as the arterial 



pressure fell and the heart recovered as the blood fluid found room 

 in the capillary-venous system and tissue spaces. 



After an injection of 69 per cent, of the normal blood quantum 

 in the period of fourteen minutes the heart worked well at first, 

 and the arterial pressure rose from 50 to 125 mm. Hg. After 

 twenty minutes the heart failed, the minute volume sank to half 



