Ill 



PREFATORY NOTE BY THE CHIEF MEDICAL 

 OFFICER. 



To The Right Hon. Neville Chamberlain, M.P., 

 Minister of Health. 



Sir, 



1. I beg to submit two reports from the Ministry's Patho- 

 logical Laboratory which form additional contributions to the 

 study of epidemiological problems by bacteriological methods. 



2. Dr. Griffith has discovered a new and simple way to 

 distinguish colonies of virulent and non-virulent pneumococci, 

 and has shown that strains derived from such different colonies 

 differ not only in virulence but in their antigenic characters. 

 This observation is of great importance in the choice of strains for 

 the preparation of protective and therapeutic sera, since sera 

 prepared with strains from the non-virulent colony have almost 

 no protective action against infections with the virulent strain. 



Further, Dr. Griffith has found that exposure of a virulent strain 

 to the action of a specific immune serum invariably leads to the 

 appearance of non-virulent colonies, and, if the exposure is 

 prolonged, to the transformation of the virulent pneumococci 

 into an entirely non-virulent strain. This fact suggests that 

 here we have one, at least, of the ways in which immune serum 

 exerts its protective action in the animal body. 



3. These observations are of wider interest, however, as a con- 

 tribution to the study of bacterial variation. In recent years 

 much attention has been given by bacteriologists to elucidation 

 of causes which determine variations in the virulence of bacteria. 

 The disconcerting fact has been brought to light that a pure 

 culture, bred from a single colony or from a single bacterium, 

 is not necessarily a collection of homogeneous individuals; it is 

 often an aggregation of units which, though all true to species, 

 differ from each other in certain biological respects amongst which 

 is the property termed " virulence." It has been shown that 

 no simple explanation of this phenomenon is possible owing 

 to the many influences concerned. 



4. Dr. Eastwood has endeavoured to extricate some general 

 principle from the confusing mass of data which have accumulated 

 around the subject of bacterial variation. He shows that these 

 observations of Dr. Griffith can be brought into line with other 



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