Chap. 12 CIRCULATION AND TRANSPORTATION BODY FLUIDS 211 



the blood ready for the emergency. In August 1944, refrigerated whole blood 

 was sent to the European and Pacific battlegrounds. The great impetus for 

 the use of whole blood that has continued in peacetime came with the dis- 

 covery of a special solution that would preserve whole blood at least 28 days. 

 The solution is known as ACD because it contains acid citrate which lengthens 

 the life of the cells, citrate of sodium that prevents coagulation, and dextrose 

 that provides nourishment. Great strides have also been made in the prepara- 

 tion and use of dried plasma. To prepare this, whole blood is centrifuged 

 as in a cream separator, thus dividing the cells from the plasma, which is 

 then frozen and dried. When the plasma is distributed, it is mixed with sterile 

 water just before using. Another important preparation, developed by Dr. 

 Edwin J. Cohn and his associates at Harvard University, was also used during 

 the war. This preparation included the isolation of the serum albumin which 

 constitutes about half of all the protein in plasma but occupies a very small 

 amount of space. Serum albumin was found to be mainly responsible for hold- 

 ing the balance of pressure between the capillaries and surrounding tissues, 

 and thus it counteracts effects of shock, such as failure of the circulation. In 

 severe shock in which there is a marked loss of blood-volume the effects on 

 the body are serious and complex. Capillaries are damaged and plasma and 

 blood cells escape into the tissues; circulation is slow and inefficient. 



Clotting of Blood 



The clotting process is a series of changes in the proteins and platelets of 

 the blood due to new conditions which arise when the organization of the 

 plasma is disturbed by a rough, jagged surface or by breaks in the blood 



PLATELETS 



FIBRIN 

 THREADS 



RED BLOOD 

 CELLS 



Fig. 12. 11. Fragment of a clot of blood highly magnified. It is a tangled mesh of 

 delicate filaments among which blood cells and platelets are entrapped. The fila- 

 ments are composed of fibrin produced during the clotting process, and appear 

 to radiate from groups of platelets. (From Best and Taylor: The Living Body, 

 ed. 3. Copyrighted by Henry Holt and Co. Reprinted with their permission.) 



