THE FLOW OF BLOOD IN THE ARTERIES 



207 



less fluid is transfused into the veins of an animal. The transfused fluid does 

 not all go to the heart at once; a considerable part of it remains in the central 

 veins, which thus become overfilled; and in the liver, which after the transfusion 

 of a large quantity may become almost as hard as a board. 



Furthermore, the entire quantity of transfused fluid does not remain in the 

 vascular system, for the vessels relieve themselves by transudation. The nature 

 of the fluid has much to do with the amount transuded. By means of blood 

 counts it has been found, for example, that after transfusion of blood, about 

 half the quantity transfused remains in the vessels at the end of the first day; 

 while if distilled water is used in transfusion the blood quickly recovers its 

 normal constitution (Worm-Miiller, Regeczy). 



Along with transudation the secretory activity of the glands increases and 

 this cooperates to diminish the quantity of fluid in the vessels. Particularly is 

 this true of the mucous membrane of the intestine and of the kidneys. If a 

 NaCl solution be transfused not too rapidly into a vein, after some time trans- 

 fusion and secretion of urine exactly balance each other (Dastre and Loye). 



Thus by transudation and secretion the quantity of fluid is gradually brought 

 back to the normal. But this takes place as a rule rather slowly, and other fac- 

 tors meantime must step in to regulate the blood pressure. One such factor is 

 vasodilation, by means of which the resistance in the vessels is lowered (Worm- 

 Miiller). Another is the activity of the heart. If transfusion be performed 



FIG. 79. Blood pressure curve, showing a sudden fall due to stoppage of the heart, as the 

 result of strong stimulation of the vagus. The time of stimulation indicated by the two 

 vertical lines. | | = ten seconds. 



slowly enough, the heart is able to throw a correspondingly larger quantity of 

 blood into the vessels and so to preserve the cardiac pressure within safe limits. 

 But if the transfusion take place more rapidly, or if the total quantity trans- 

 fused be very large, the heart may drive more blood into the vessels than before 

 the transfusion but not enough to prevent stasis of blood in the heart. Finally, 



