34 



Summary. 



It is now recognised that the study of bacterial variation is of 

 practical importance, because the subject is concerned with 

 variations in the capacity of bacteria for producing disease. 



One is confronted with a confusing mass of data, ranging from 

 some minor and temporary change in a single function to the 

 much more profound alterations, popularly known as "the 

 Twort-d'Herelle phenomenon," where the vitality of the bacteria 

 is seriously imperilled and relatively few individuals survive. 



It would simplify the matter if one could recognise some general 

 principle underlying this apparent confusion, and could attribute 

 the different types of variants to different phases in the operation 

 of this principle. 



In the search for a common factor, it is observed that these 

 changes only occur with living and actually growing bacteria 

 and that, therefore, they are probably due to some influence 

 which operates at the nascent stage of growth. Hence the 

 common factor can only be explained in terms of vital processes ; 

 but about these no precise information is available. 



Still, it is possible to formulate a general statement. The 

 constituents of living bacterial protoplasm have two functions, 

 catalytic action, i.e., the preparation of food material with the 

 aid of their appropriate enzymes, and synthetic action, i.e., the 

 building up of new protoplasm. It is obvious that the balance 

 between these two activities must be very minutely adjusted 

 and that any disturbance of this balance will tend to the pro- 

 duction of variants. 



My report is concerned with the development of this theme 

 in relation to known facts about bacterial variants. 



January, 1923. 



Printed under the authority of His Majesty's Stationery Office 



By Eyre and Spottiswoode, Ltd., East Harding Street, E.C 4, 



Printers to the King's most Excellent Majesty. 



