Exercise XVI 



BLOOD AND CIRCULATION 83 



drop of the cell suspension on each half of the 

 slide. To the drop on one side, add a drop of 

 anti-A serum, to which a blue dye has been 

 added; and to the drop on the other side, add a 

 drop of anti-B serum, which has been dyed 

 yellow. (Be sure to mark which is which!) 

 Mix the drops by jittering the slide gently for 

 15 to 20 seconds, being careful not to let the 

 drops run into each other. Can you observe 

 any agglutination? Place cover slips on the slide 

 and examine both drops under the microscope. 

 Compare with a drop of blood suspension to 

 which no serum has been added. What is your 

 blood group? 



Recently a number of blood factors in addi- 

 tion to the A, B, AB and O groups have been 

 discovered. Probably the most important of 

 these is the Rh factor. About 85% of the white 

 race and 99 to 100% of certain other groups 

 (Chinese, Japanese, African Negroes, and 

 North American Indians) have an antigen called 

 the Rh factor in their red blood cells. (The ab- 

 breviation "Rh" refers to the Rhesus monkey in 

 whose erythrocytes, as part of the cell mem- 

 brane, this antigen was first discovered.) Blood 

 containing the Rh factor is known as Rh- 

 positive; that lacking it, Rh-negative. If blood 

 from an Rh-positive person is transfused into 

 an Rh-negative recipient, an antibody (anti-Rh 

 factor) is produced. This in itself is not harmful, 

 but if a second transfusion is given, the anti-Rh 

 antibody which has accumulated in the recipi- 

 ent's blood reacts with the Rh antigen introduced 

 with the new red blood cells, and the result is 

 often fatal. 



The anti-Rh antibody may also be produced 

 in an Rh-negative woman who, having an Rh- 

 positive husband, bears Rh-positive children. 

 During pregnancy some fetal red blood cells 

 containing the Rh antigen may leak into the 

 mother's circulation and cause the formation of 

 anti-Rh antibody. This has no ill consequences 

 for the mother, unless she later receives a trans- 

 fusion of Rh-positive blood. Usually also the 

 first child is not seriously harmed, since the 

 mother's antibody titer is still low. During 

 later pregnancies, however, the mother's anti-Rh 



antibody may enter the fetal circulation and 

 destroy the fetal blood cells. This condition, 

 known as erythroblastosis fetalis^ causes the 

 death of the child, unless its blood can be re- 

 placed in a massive transfusion by Rh-positive 

 blood free from the antibody. 



The test to determine the presence of Rh factor 

 in blood is tricky, and inaccurate results are often 

 obtained unless great care is taken to standardize 

 the procedure. For this reason we will not at- 

 tempt it in this laboratory. 



THE HEART 



(Do not fail to read Wiggers's fine paper listed 

 in the Readings. Bring it to the laboratory, if 

 possible.) 



The heart, which is a single, two-chambered 

 organ in fishes, is a double organ in the birds and 

 mammals, with a lung heart on the right and a 

 body heart on the left. The right atrium (auri- 

 cle) receives blood drained by the veins from the 

 tissues throughout the body and passes it into 

 the right ventricle, which pumps it to the lungs 

 for gas exchange. The oxygenated blood is 

 brought back to the left atrium, which passes it 

 to the left ventricle, which sends it out through 

 the arteries to the body tissues. 



The heartbeat has an associated pattern. First 

 the atria, their walls relaxed, distend with blood. 

 Then the atria contract while the ventricles re- 

 lax, transferring the blood to the ventricles. 

 Then the ventricles contract, driving the blood 

 to the lungs and tissues, the bicuspid and tri- 

 cuspid valves preventing it from re-entering the 

 atria. Similarly the semilunar valves prevent any 

 suck-back of blood from the aorta and pul- 

 monary artery during the next relaxation of the 

 ventricle. 



Body tissues — > venae cavae — > right atrium 



tricuspid semilunar 



* right ventricle — > pulmonary 



valve 



artery 

 atrium 



valve 



body tissues 



-^ lungs 



bicuspid 



valve 



pulmonary vein 



left 



semilunar 



* left ventricle — ^ aorta 



valve 



