LIMITATIONS 47 



Avery and Goebel were thus ready to attack the final 

 problem rich in significance and consequences, the synthesis 

 of an artificial bacterial antigene, obtained by combining the 

 polysaccharide of a pneumococcus with a foreign protein. 

 With this end in view they chose the sugar of type III which, 

 being totally deprived of nitrogen, can be considered as a 

 definite chemical entity and has never by itself determined 

 any immunological response on the part of the injected animal. 

 It is not only inactive in a pure form, but the microbe from 

 which it is isolated does not in the majority of cases possess 

 the power to bring forth antibodies in rabbits. 



The great difficulty from the chemical point of view 

 consisted in preparing by synthesis the substance derived 

 from the polysaccharide capable of combining with a protein 

 without neutralizing or masking the chemical groups. This 

 feat was accomplished by Goebel, a young and brilliant pupil 

 of Heidelberger. He obtained the 'amino-benzyle-ether' of 

 sugar type III which he combined with a foreign animal 

 protein, the globulin of horse serum. This soluble antigene 

 has nothing in common with the pneumococcus type III 

 excepting the polysaccharide, and yet the rabbits into which 

 it was injected reacted by manufacturing specific antipneumo- 

 coccic antibodies in their serum. The serum of these animals 

 not only precipitates the synthetic antigene, but specifically 

 agglutinates the living cultures of pneumococcus type III and 



NH, 



I o 



H— C— OH/ .- 



Ho=C— OH H2=C— OH 



Glucoside Galactoside 



It can be seen that the only difference consists in the position of H 

 and OH at the level of the fourth carbon atom. 



