182 The Vertebrate Organ Systems 



bodies. The antigen or the material which causes the antibody forma- 

 tion is carried in the red blood cells. Normally there are no anti- 

 bodies present in the serum of the Rh-negative individual ; therefore, 

 there are no adverse reactions. The first transfusion of Rh-positive 

 blood will not injure the Rh-negative recipient, but does result in the 

 formation of antibodies. A subsequent transfusion of Rh-positive blood 

 will result in death. 



This reaction is of particular interest due to the role which it often 

 plays in maternity cases. If a pregnant woman is Rh negative, and 

 her husband is Rh positive, the fetus may inherit the positive factor. 

 In this case the woman will develop Rh antibodies. The first child 

 is usually born normally, but a second pregnancy may result in abortion. 

 This is due to the fact that the antibodies in the mother's blood can 

 cross the placenta and destroy the red blood cells of the fetus. 



THE LYMPHATIC SYSTEM 



While the circulatory system by means of its smaller vessels and 

 capillaries is able to bring the blood into all regions of the body, it 

 is not able to bring all the elements into direct contact with the individual 

 cells. This is the function of the lymphatic system. Without the 

 lymphatic system to supplement the circulation, the circulatory system 

 would be powerless to bring food to the individual cells or to pick up 

 waste materials. 



That part of the plasma with its dissolved food materials, hormones, 

 proteins, etc., which escapes through the capillary walls is known as 

 tissue fluid. A few white blood cells also escape with this fluid, but the 

 red blood cells are held back by the capillary walls. This tissue fluid 

 bathes the neighboring cells, giving up its foods and other materials, 

 and in turn picking up waste materials. Its composition is then changed. 

 After performing these functions, it enters the small channels, the lymph 

 capillaries, and is known as lymph. The capillaries unite to form larger 

 lymph vessels or lymphatics. By means of these vessels, the lymph is 

 carried back into the veins and the circulatory system proper. 



The movement of the lymph through the lymphatics toward the 

 thoracic cavity is accomplished by a combination of several different 

 factors in mammals. While the lymph vessels are thinner than the 

 veins, they superficially resemble them by having many valves to pre- 

 vent backward fiow. In part, the upward flow is maintained by the 

 constant pressure of fluid moving into the vessels. Muscular movements 



