BLOOD TRANSFUSION 215 



3. Transfusion of physiologic salt solution, or injecting directly 

 into a vein. A more serious measure. Here the blood stream is 

 invaded at once and good or bad effects are caused promptly. 

 Accuracy is essential, that the injected fluid should be exactly of 

 the right density and that nothing else whatever should enter the 

 vein, lest clot formation occur. 



Why are saline fluids introduced into the vessels? (i) To 

 restore volume to the blood and maintain proper tension in the ves- 

 sels, thus assisting the action of the heart; (2) to secure the tis- 

 sues from loss of water and injuries due to disturbances in osmotic 

 pressure; (3) to insure the distribution of normal red cells; (4) 

 to dilute the poisons which are not eliminated during processes of 

 disease, as in uremia. 



Direct transfusion of blood is accompanied by a special danger 

 because it is possible that the blood cells of one individual may 

 act injuriously upon those of another, causing disintegration or 

 hemolysis of red cells. (See Glossary.) 



The blood of the donor (the person who gives it) may be hemolytic to 

 that of the patient; that is, it will cause hemolysis of the patient's cells. 

 Still more to be avoided is the situation where the patient's blood is hemolytic 

 to that of the donor. Fortunately this accident need no longer occur, since 

 laboratory tests can be made which will insure the selection of a donor whose 

 blood will agree with that of the patient. 



Blood transfusion is resorted to after severe hemorrhage, also 

 in certain diseases, as leukemia, in which the red cells are dimin- 

 ished in number. 



Rapidity of heart action does not necessarily move the blood any 

 faster through the vessels, as the rapid heart is frequently a weak 

 heart. Also the short cardiac cycle signifies that the diastole is 

 shortened; the chambers cannot receive as much blood; conse- 

 quently, less is sent out. 



Another effect of the weak and rapid heart is to deprive it of 

 proper resting time. It wears itself out. 



Quite different is the normal acceleration of heart action in the 

 course of muscular exercise; this really sends the blood more 

 abundantly through the body. The auricles are well filled, the 

 ventricles contract forcibly and the cardiac cycle, although short, 

 is efficient. 



Variations in the blood flow are influenced in the vessels by 



