more. In this case no contact with the dam- 

 aged tissues has been allowed, and the plate- 

 lets fail to disintegrate as quickly when they 

 come into contact with an oiled surface. 



Anticoagulants. Anticoagulants are com- 

 pounds that prevent, or definitely inhibit, 

 blood clotting. Citrate, fluoride, and oxalate 

 salts all have the common property of remov- 

 ing ionic calcium from the blood; and these 

 anticoagulants are used very commonly in 



The Circulatory System - 325 



However, in the case of blood, the reacting 

 components are called agglutinogens and 

 agglutinins, the agglutinogens being present 

 in (or on) the red cells and the agglutinins 

 in the plasma. In man's blood there are two 

 agglutinogens, namely A and B, and two 

 agglutinins, a and b; and the four main 

 blood groups of man are determined by the 

 presence or absence of these components, as 

 is shown in Table 17-3. 



Table 17-3— Blood Types in Man 



Blood Agglutinogens Agglutinins Can Donate Can Receive 



Groups [in corpuscles) {in plasma) to from 



A A b A, AB O, A 



B B a B, AB O, B 



AB A and B none AB O, A, B, AB 



O none a and b O, A, B, AB O 



handling blood for routine analysis. Blood- 

 sucking creatures, such as leeches, produce 

 organic anticoagulants. Typically these re- 

 agents interfere with the formation or activ- 

 ity of thrombase, as is the case for hirudin, 

 the anticoagulant of the leech. In normal 

 circulating blood there appears to be an un- 

 identified anticoagulant, but this is neutral- 

 ized by thromboplastin when coagulation 

 occurs. Also a very powerful anticoagulant, 

 heparin, can be extracted from liver and 

 muscle tissues. 



Blood Types in Relation to Transfusion. 

 Transfusions have saved many lives in cases 

 of severe hemorrhage, and in other cases 

 where the blood volume falls so low that the 

 heart no longer can maintain the circulation. 

 But the early history of blood transfusion 

 was beset with many tragedies, until 1900, 

 when Landsteiner developed an understand- 

 ing of the blood types of man. Previously the 

 many deaths had resulted from the mixing of 

 incompatible bloods, which leads to a clump- 

 ing (agglutination) of the red corpuscles and 

 consequently to a blocking of the capillary 

 circidation. 



The agglutination of blood corpuscles rep- 

 resents a typical antigen-antibody reaction. 



When a transfusion is necessary every effort 

 is made to find a donor belonging to the same 

 group as the recipient. Also, whenever pos- 

 sible, a test of compatibility is performed be- 

 fore the transfusion is started. However, if 

 such a donor is not available, the other com- 

 binations shown in Table 17-3 may be em- 

 ployed. For example, type O, which is called 

 a universal donor, may give blood to a type 

 A recipient. In this case, the donor corpus- 

 cles, lacking any agglutinogen, are not 

 clumped by the recipient's plasma, and the 

 recipient's corpuscles escape agglutination 

 because the agglutinins of the donor plasma 

 become so diluted by the plasma of the re- 

 cipient that they do not retain much, if any, 

 activity. 



The blood types of man and other mam- 

 mals are inherited in Mendelian fashion (p. 

 481) and do not change during the lifetime 

 of the individual. Also, there is another herit- 

 able agglutinogen, the Rh factor, 1 although 

 the importance of this antigen was not appre- 

 ciated until recently. Among white people, 

 about 85 percent of the population are Rh 



1 So named because it was first identified in the 

 rhesus monkey. 



