44 THE BIOLOGICAL PROBLEM 



It was a brilliant confirmation of the splendid work of 

 Landsteiner on complex antigenes. His researches led him 

 to conclude that biological specificity is conditioned by 

 chemical groups relatively small with respect to the antigenic 

 molecules. A new proof in favour of this thesis was given 

 by Avery, as we shall see presently. 



Thus the specificity of different types of pneumococci 

 depends on the chemical nature of the sugar which forms the 

 capsule. What would happen if the microbe could be relieved 

 of this capsule. Would it die? Would it conserve its virulence? 

 Of what nature would be its specificity and what accidents 

 would it occasion in an animal? All these problems were 

 completely solved by Avery with the collaboration of a young 

 Frenchman, Rene Dubos. But it required several years to 

 do it, as no enzyme capable of attacking, dissolving, in other 

 words, of digesting these sugars could be found. Finally, 

 Dubos isolated from the bogs of New Jersey, a microbe of 

 the soil, which secreted an enzyme capable of digesting the 

 capsule of pneumococcus type III, without killing the cell. 



It was now possible to obtain cultures of pneumococci having 

 totally lost the type-specificity^ deprived of virulence and incap- 

 able of invading the animal -in which they were injected. 

 However, these microbes had not lost the faculty of surrounding 

 themselves with a new capsule which restored their specific 

 virulence. But it became possible to give these cells the faculty 

 of surrounding themselves by the characteristic sugar of a 

 different type and of transforming themselves into pneumococ- 

 cus types I or II. A degenerated microbe can produce any kind of 

 specific saccharide, according to conditions in which it is placed. 



The authors then had the idea of injecting doses of these 

 enzymes into the bodies of the experimental animals — mice — 

 so as to discover whether they would digest the capsule of the 

 virulent pneumococci in vivo and render them inoffensive. 

 They ascertained that their previsions were fully justified and 

 that it was possible to protect mice specifically against 

 type III, and solely against this type. 



They afterwards studied the chemico-immunological 



