82 PHYSIOLOGY. 



fusion the blood is first drawn into a receptacle. In indirect transfusion 

 the blood is often defibrinated before transference. The blood may be 

 introduced either into an artery or a vein ; if into a vein it is sent in 

 the direction of the natural flow, i.e. toward the heart ; if into an artery, 

 in either direction. Soon after the discovery of the circulation of the 

 blood the operation of transfusion began to be practiced, and high 

 hopes were indulged in as to its value. But it was soon found to be 

 attended by so much danger that it is now seldom used. It is resorted 

 to (i) after great loss of blood, (2) after some forms of poisoning part 

 of the blood is withdrawn and replaced by fresh blood, and (3) in 

 certain disordered conditions of the blood. The chief dangers are (i) 

 the introduction of air which forms minute bubbles and stops the blood- 

 flow in the capillaries, (2) the introduction sometimes causes coagula- 

 tion within the blood vessels, and (3) the serum of the introduced 

 blood sometimes destroys the corpuscles of the blood to which it is 

 added. In the earlier practice lamb's blood was employed, but now 

 when transfusion is practiced on man only human biood is used. It 

 has been found safer and better after great loss of blood from hemor- 

 rhage, to introduce a salt solution of about the natural degree of salt- 

 ness of the blood ; this restores the normal volume of circulating liquid, 

 and avoids most of the dangers except that of introducing air. The 

 numerous fatal results of this operation have shown that it should not 

 be resorted to except in cases of extreme necessity. 



For directions about stopping the flow of blood from 

 wounds see Chapter XXIII. and the books named below. 



READING. Prompt Aid to the Injured, Doty ; Emer- 

 gencies, Dulles; Emergencies, Howe; First Aid to tJie 

 Injured, Lawless; First Aid to the Injured, Morton; First 

 Aid in Illness and Injury, Pilcher ; Sickness and ^Accidents, 

 Curran. 



What other process keeps pace with the coursing of the 

 blood through the body, being its running mate, so to 

 speak ? 



Summary. i. Blushing, and other variations in blood supply, are 

 under the control of the sympathetic nervous system. 



2. The sympathetic nervous system consists of two rows of ganglia 



