40 THE BIOLOGICAL PROBLEM 



an unknown fate than a drop of water can travel up- 

 stream. 



We will now try to show what important results may be 

 obtained by applying chemical and physical methods to a 

 biological problem, and we will take as an example a problem 

 of capital importance: immunity. 



The experimental work which illustrates our thesis was 

 chosen not only because of its recent and fundamental charac- 

 ter, but also because it represented the last link in a chain 

 which was started at the beginning of the twentieth century 

 and forged with scientific rigour and admirable logic by the 

 scientists whose names we have already mentioned: Obermayer 

 and Pick and, especially, Karl Landsteiner. The latter, not 

 long ago, obtained the Nobel Prize for Medicine for his dis- 

 covery of the four blood-groups. This discovery, as everybody 

 knows, made blood transfusions absolutely safe. Our choice 

 was therefore not only governed by the interest of the work 

 itself, but by the fact that it is soHdly based on a long series 

 of previous discoveries which rendered it possible. It also 

 enables us to foresee a still longer series of discoveries to come. 



We shall now briefly report the experiments of Dr. Oswald 

 Avery and his collaborators, Drs. Michael Heidelberger, Rene 

 Dubos, and Walter Goebel, which represent the perfect type 

 of research in modern biology. This work was done in the 

 laboratories of the Rockefeller Institute in New York. 



Pneumonia is one of the diseases which cause the greatest 

 havoc in the United States. In the great majority of cases it 

 is due to a micro-organism called 'pneumococcus'. We have 

 known for a long time that there are very distinct differences 

 in pneumococci which manifest themselves by a characteristic 

 specificity. They develop in the same way in artificial media, 

 but even though their aspect under the microscope is the 

 same, they can be classed in well-defined and specific types 

 which simply bear a number: types I, II, III, etc. The 

 differences existing between these types are not revealed by 



