208 THI-. INTIRNAL I;NV1R()N M IN I C)l I III HODV •'i'lt HI 



AllliDUgh the lympluKytcs arc the greatest wanderers ol all blood cells, 

 little is known about their liinction. They work their way out through the 

 walls of blood vessels, lymph vessels, and the lining of the alimentary canal. 

 The tonsils and the appendix are loaded with them (Fig. 12.9). Great migra- 

 tions of lymphocytes accompany certain types of inllammation. 



Variations in the Numbers. Certain normal physiological conditions, 

 among ihcm muscular exercise and pregnancy, cause an increase of leuco- 

 cytes. Quick shifts in temperature and in states of mind may result in their 

 immediate increase in the blood as if they had suddenly moved from the sides 

 of the blood vessels out into the currents (Fig. 12.10). There are also daily 

 rhythms with an afternoon rise, in order to determine what type of cell has 

 increased, it is necessary to make diiTercntial counts. Stained preparations 



'■• 



'• ■■ li^::^ 



Fig. 12.9. Drawings of a leucocyte (neutrophil) at one-half-minute intervals 

 to show its movement and ability to consume bacteria, represented by dots. Myriads 

 of such cells arc continually moving about in the body. (From Best and Taylor: 

 The Liviufy Body, ed. 3. Copyrighted by Henry Holt and Co. Reprinted with 

 their permission.) 



of blood are examined and since different types of leucocytes stain differently, 

 it is easy to distinguish them. Several hundred leucocytes arc counted and the 

 various types are recorded separately. The percentage of each type is then 

 calculated. 



Blood Platelets. The blood platelets (thrombocytes) are about one-quarter 

 the size of the red cells. They have no nuclei, seem to be fragments of certain 

 giant cells of the red bone marrow, and are usually clumped together. They 

 play an important part in the coagulation of blood, but beyond that their 

 function is unknown (Fig. 12.11, and Table 12.2). 



Human Blood Groups. Whenever foreign proteins such as those of bac- 

 teria are taken into the blood stream of an animal, the cells of the body pro- 

 duce antibodies, counteracting substances that immunize foreign matters. 

 Antibodies are produced abundantly by the cells of the blood. The foreign 

 proteins that stimulate the production of antibodies are called antigens. "No 

 smoke without a fire" might be changed to "no antibody without an antigen." 



Whenever one or another kind of antigen and antibody are brought to- 

 gether, a characteristic reaction occurs. If the antigen is a poison, the antibody 

 that neutralizes it is called an antitoxin. Foreign cells, such as bacteria or alien 

 blood cells, may get into the human blood stream by injection. Although 



