82 BLOOD AND CIRCULATION 



Exercise XVI 



tion has the same osmotic pressure as the blood 

 and will keep the blood cells in good condition. 

 This suspension of blood cells will be used for 

 blood typing.] 



The drop of blood that has been placed on the 

 slide should be spread evenly and very thinly 

 by drawing it along the slide with the end of a 

 second slide. When the film of blood has dried, 

 cover it with a few drops of methyl alcohol, and 

 let it stand for 2 or 3 minutes. Drain off the 

 alcohol, and immerse the slide for 6 seconds in 

 the red stain which has been provided. Then 

 rinse in a gentle stream of tap water for a few 

 seconds. Allow the slide to drain again, and 

 immerse for 6 seconds in the blue stain. Rinse 

 again in tap water, drain, and examine under 

 the microscope. 



Identify the various types of blood cells. Most 

 common of course will be the erythrocytes, 

 which appear red. The nuclei of the leucocytes 

 stain blue; it should be possible to tell the 

 difference between the lymphocytes and granulo- 

 cytes by the shapes of their nuclei. 



BLOOD GROUP TYPING: 



AN ANTIGEN-ANTIBODY REACTION 



The entire human race can be divided into 

 four categories on the basis of their blood types 

 (A, B, AB, O). Erythrocytes may contain anti- 

 genic proteins on their surfaces, designated A 

 or B, or AB, if both are present. If neither anti- 

 gen is present, the letter O is used. Persons of 

 the A type have in their serum an antibody 

 known as anti-B, which specifically reacts with 



erythrocytes containing the antigen B. Similarly, 

 persons of the B type have an antibody, anti-A, 

 which reacts with A erythrocytes. Blood of 

 type O contains both anti-A and anti-B anti- 

 bodies, and AB blood contains neither of these 

 antibodies. 



If the blood from an A person is transferred 

 into a B person the antibodies of the host serum 

 react with the antigens of the donor's red blood 

 cells and cause them to clump together or 

 agglutinate. This blocks the blood vessels and 

 may kill the person. It is the antigen more than 

 the antibody of the donor which causes severe 

 damage when injected into an incompatible 

 person, since the bulk of the blood cells ag- 

 glutinated are those of the donor. What happens 

 when B blood is transfused into an A recipient ? 



Although blood-group typing is an example 

 of an antibody-antigen reaction, it is unusual in 

 that these antibodies are present in the cir- 

 culatory system without having been stimulated 

 by an invasion of foreign material. Usually anti- 

 bodies are made only in response to the presence 

 of a foreign antigen. Yet no blood group antigen 

 need ever have been present in man for the blood 

 group antibodies to develop. 



Blood groups are determined genetically. 

 They are distributed differently in the various 

 human races. The distribution among white 

 Americans is as shown in the table, where the 

 plus sign indicates agglutination or clumping of 

 cells. 



To determine your blood grouping, use the 

 suspension of cells that you prepared in normal 

 saline solution. Draw a line across the middle of 

 a microscope slide with a wax crayon. Place 1 



