142 Perspecf'ives in Microbiology 



more acute form. An impressive beginning on these was 

 made with the sugars by Avery and Goebel, who showed, 

 among many other things, that the mere rotation of a 

 single carbon atom in the chain through 180°, as in carbon 

 4 on passage from glucose to galactose, was capable of caus- 

 ing a profound change in specificity when these sugars 

 were coupled to proteins. And I shall tell of some more re- 

 cent experiments with polysaccharides from our own labo- 

 ratory. But knowledge of the fine structure of the proteins 

 is in its infancy, and so we know nothing of the chemical 

 basis of species or organ specificity or how, if at all, an 

 antibody differs chemically from the corresponding normal 

 globulin. 



A major subproblem is concerned with the chemical 

 differences between the blood groups. So far, the hapless 

 victim of improperly matched bloods can tell the difference 

 far more certainly than the immunochemist, who has recog- 

 nized mainly similarities. But the studies of Morgan and 

 of Kabat are beginning to disclose subtle distinctions 

 among the blood group substances. I shall refer to these. 



How does complement "fix" to antigen-antibody systems, 

 and how does complement mediate the lysis of sensitized 

 cells? Is complement or one of its components an enzyme? 

 What is allergy, and how is it related to immunity? I might 

 multiply examples indefinitely. But let us return to the 

 antibodies and consider the gaps in our knowledge of 

 them. 



Antibody Formation 



In what organs, or in what cells, are antibodies made? 

 The earlier workers implicated the cells of the reticulo- 

 endothelial system, for it is by these cells that inert parti- 

 cles and bacteria are taken up and removed at least tempo- 

 rarily from the blood stream. Florence Sabin, in 1939, with 

 an antigenic dye prepared in our laboratory gave circum- 



