Problems in Immunology 149 



ConsfJfution and Specificify of Blood Group 

 Substances 



The blood group substances present additional puzzles 

 in the relation between constitution and specificity. A 

 most striking finding by all of the more recent workers in 

 this area was the great similarity of the A, B, and O sub- 

 stances, in spite of the dire consequences of the transfusion 

 of mismatched bloods. All three substances were found to 

 consist of galactose, fucose, N-acetylglucosamine, and N- 

 acetylgalactosamine, together with a residue of amino acids. 

 The cross reactivity of the blood group substances in Type 

 XIV antipneumococcus serum has long been known and 

 has been quantitatively studied by Kabat, but it is still not 

 known whether this reactivity is due to the multiple re- 

 currence of certain galactose linkages or whether it is 

 caused by the N-acetylglucosamine portions. Possibly both 

 types of residues function. Leskowitz and Kabat recently 

 devised a new method for the separation and quantitative 

 estimation of glucosamine and galactosamine, and with its 

 aid have shown that hog and human blood group A 

 substances gave glucosamine to galactosamine ratios averag- 

 ing 1.5, hog and human 0(H) 2.3 and 2.6, and human B 

 2.8. It is thus evident that chemical differences among the 

 blood group substances are beginning to emerge, and the 

 outlook along these lines appears hopeful. 



Nature of Complement 



We now come to complement, which remains in large 

 part an enigma despite its importance as an auxiliary in 

 immunity and its enormous use in diagnostic tests carried 

 out daily all over the world. True, our own experiments 

 showed that complement could be weighed, and so disposed 

 of the widely held view that complement was merely a 

 colloidal state of fresh serum proteins. These studies also 



