BLOOD GROUPS 55 



tern. They may occur in two forms : water soluble and lipid soluble 

 (i.e., soluble in lipid solvents such as alcohol-ether mixtures and 

 chloroform). All individuals apparently have the lipid-soluble form 

 in their tissues, in conformity with their blood group (Boyd and 

 Boyd, 1937). The water-soluble form, however, is found in only 

 about 85 per cent of European individuals. Such persons are called 

 secretors, and those in whose tissues and body fluids water-soluble 

 antigens corresponding to their blood group are not found are called 

 nonsecretors (Schlff and Sasaki, 1932). The ability to secrete the 

 A and B antigens in water-soluble form is inherited, being con- 

 trolled by a pair of genes S and s. 



The saliva of all secretors, no matter what their group, contains 

 enough of the H antigen to make it possible to diagnose such in- 

 dividuals by the inhibition technique with an anti-H reagent such 

 as Ulex extract (Boyd and Shapleigh, 1954b). Saliva of group O 

 secretors is richest in H antigen, and, according to Race and Sanger 

 (1958), some AiB salivas may not contain enough H antigen to 

 make the use of Ulex extracts reliable for the diagnosis of secretors in 

 this subgroup. 



The above sketch does not by any means give an adequate picture 

 of the ABO blood group system, which is one of the most complicated 

 known in man. A good discussion is given in the book by Race and 

 Sanger (1948). We may simply mention that a number of other 

 variants of the A antigen are known, all of them fortunately rare, 

 and that genes exist, also rare, which can modify the expression of 

 the ABO genes. The "Bombay" gene, x, when present in double 

 dose, XX, prevents the development of antigens B and H ; whether 

 it also suppresses A is not yet known. There seems to be another 

 gene, y, which when present in double dose, yy, modifies the de- 

 velopment of the A antigen in the red cells and, to a much lesser ex- 

 tent, in the saliva. Variants of the B antigen have also been observed. 



Blood Groups of the Ancient Dead 



Antigens A and B are much more stable than most protein antigens. 

 (The chemical nature of the A and B antigens will be discussed in 

 Chapter 7.) It is comparatively easy to demonstrate A and B in 

 dried tissue, boiled erythrocytes, or tissues which have been pre- 

 served in formaldehyde. These facts led Boyd and Boyd (1934, 



