46 THE BIOLOGICAL PROBLEM 



polysaccharides, but under some other form, for example, chemi- 

 cally combined with a protein or another substance which gives 

 them an antigenic power of which they themselves are deprived. 

 In order to see what would be the consequence of the 

 introduction of a radical 'carbohydrate' in a protein molecule, 

 from the point of view of the orientation of the specificity of 

 the new compounds thus formed, Avery and Goebel chose 

 two simple sugars (monosaccharides), glucose and galactose. 

 These two substances have the same composition and the 

 same chemical formula. They differ one from the other 

 only by their configuration in space, the groups H (hydrogen) 

 and OH (oxhydril) fixed to one of the carbon atoms occupying 

 a different place in each case. Starting from these two sugars, 

 Goebel succeeded in synthesizing the corresponding 'para- 

 aminophenol-glucosides'. Then each of these derivatives of 

 the sugar was combined with a protein (globulin of serum or 

 egg albumin) so as to obtain definite compounds (sugar-azo- 

 proteins), that for simplification can be called galacto-globulin, 

 galacto-albumin, gluco-globulin, and gluco-albumin. Rabbits 

 were immunized with these substances, and the sera of these 

 animals, containing the antibodies, were submitted to immuno- 

 logical reactions similar to those of which we spoke above. 

 It was found that the specificity of each of the compounds 

 thus created, was solely determined by the radical sugar, and 

 altogether independent of the nature of the protein to which 

 it was combined. This fact was capital. The introduction of 

 a simple sugar in a protein confers to the entire compound 

 a new specificity which is determined by the chemical structure 

 of the carbohydrate. The sugars in question differ only by 

 the spatial relations of the groups OH and H attached to the 

 fourth carbon atom. A simple rotation of i8o degrees around 

 this atom suffices to change completely the serological speci- 

 ficity of two substances otherwise identical. The marked 

 differences between pathological accidents can then be due 

 to the simple displacement of a chemical group in a molecule.^ 



' The similarity between the two substances, the /)-aminophenol 

 P-glucoside and the />-aminophcnol p-galactoside clearly appears in 

 the two structural formulas: 



