R. J. DUBOS 



the ability to produce its specific capsular polysaccharide an extract 

 of the cell of another type of encapsulated pneumococcus, one can 

 convert the former organism into the type from which the extract was 

 made. From then on, the cell can produce, and transfer to its progeny 

 the ability to produce, a polysaccharide different from the one it had 

 been known to synthesize heretofore. All available evidence indicates 

 that the substance which is capable of inducing the transformation is 

 a form of desoxyribonucleic acid- — specific for each pneumococcus 

 type (4). Of equal interest is the unavoidable conclusion that the 

 bacterial cell is not only an integrated complex of independent charac- 

 ters, but that it is possible to substitute for one of these characters an- 

 other one, homologous but different, without interfering essentially 

 with cellular organization. 



Thus, a large body of knowledge concerning cytology is slowly 

 emerging from the study of bacterial variability and of the behavior of 

 the cell in the presence of a number of biological reagents. It is be- 

 coming possible to recognize and to define in chemical terms a number 

 of structures not yet detectable by any microscopic technique. Further- 

 more, by bold, even though admittedly dangerous, extrapolation, one 

 can guess at the approximate position of these cellular constituents 

 in the architecture of bacteria. The history of science provides, of 

 course, many examples of the fruitfulness of indirect methods, and in 

 particular of the utilization of chemical and biological manifestations 

 as indices and guides for the recognition and identification of morpho- 

 logical structures. Claude Bernard stated as early as 1855 that 

 "anatomical localization is often revealed first through the analysis 

 of the physiological processes." Much of the morphology indirectly 

 revealed by antibodies, enzymes, and cytotoxic substances lies beyond 

 the microscopic range and in fact often reaches the molecular level. 

 It concerns the organization of those molecular groupings which, 

 because of their chemical reactivity, condition the behavior of the cell 

 both as an independent functioning unit and in its relation to the 

 environment. This knowledge is of obvious interest to the cytologist. 

 It also forms the fundamental basis upon which is being erected the 

 theory of immunity, since all the phenomena of host-parasite relation- 

 ship are essentially a reflection of the biochemical architecture of the 

 cell. 



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