328 A. C. R. Dean and Sir Cyril Hinshelwood 



yield of the first batch prove viable in the second. The cycle 

 is repeated with gradual increase in concentration and event- 

 ually a highly resistant strain is obtained. One very interest- 

 ing run of film shown by Hughes presents in parallel two small 

 groups of cells, one (A) subjected to the action of chloram- 

 phenicol, and the other (B) not. The successive patterns 

 observed in the two cases follow a sequence as nearly as may 

 be seen identical, except that (A) appears as a slowed-down 

 version of (B). 



The processes made visible in these records are not those 

 suggested by theories ascribing the development of resistance 

 solely to the selection of rare mutants. All the cells visible on 

 the film at a given moment appear to be growing, although 

 more slowly in presence of the drug than in its absence. They 

 are clearly performing sufficient of their total complement of 

 biochemical reactions to achieve material synthesis against 

 the action of the inhibitor. After each cycle in the series of 

 transfers the yield of cells which can be transferred to a 

 higher concentration with prospects of survival is as much as 

 one in two. From these observations, therefore, it seems 

 clear to us that active adjustments in the cell economy occur. 



REFERENCES 



Arley, N. (1955). Nature (Lond.), 176, 465. 



Earner, H., and Cohen, S. S. (1954). J. BacL, 68, 80. 



Earner, H., and Cohen, S. S. (1957). J. BacL, 74, 350. 



Easkett, a. C, and Hinshelwood, Sir Cyril (1950). Proc.roy.Soc.B, 



137, 524. 



Easkett, A. C, and Hinshelwood, Sir Cyril (1951a). Proc. roy.Soc. B, 



138, 75. 



Easkett, A. C, and Hinshelwood, Sir Cyril (19516). Proc. roy.Soc. B, 



138, 88. 

 Een-Ishai, R. (1957). Biochim. hiophys. Acta, 26, 477. 

 BoiviN, A., Vendrely, R., and Vendrely, C. (1948). C. R. Acad. Sci. 



(Paris), 226, 1061. 

 EuTLER, J. A. V. (1956). Radiat. Res., 4, 20. 

 Caldwell, P. C, and Hinshelwood, Sir Cyril (1950). J. chem. Soc, 



p. 1415. 

 Caldwell, P. C, Mackor, E. L., and Hinshelwood, Sir Cyril (1950). 



J. chem. Soc, p. 3151. 

 Caspersson, T. (1947). In Symp. Soc. exp. Eiol., No. 1, p. 127. 



