THE UNIQUENESS OF THE INDIVIDUAL 



nutritional status, or by treatment with enzymes (Kimball, 

 1947). 



It is clear that the cytoplasm of Paramecia is malleable in a 

 way completely foreign to our conception of the propagation 

 system of the chromosomes, and that this malleability endows 

 them with what is, in effect, a cytoplasmic genetic memory. 

 We shall not delay with interpretations of the mechanism of 

 the adaptive response, except to say that all turn upon the idea 

 of an intracellular competition, whether between self-perpetu- 

 ating cytoplasmic particles or between reaction sequences that 

 are mutually inhibitory and so mutually exclusive. Such an 

 interpretation gives point to Hinshelwood's comment that 

 inheritance which is Lamarckian in terms of cells should be 

 described as Darwinian at the level of cellular ingredients (see 

 Section 1). 



(ii) Adaptive transformations in micro-organisms. The ""train- 

 ing** of micro-organisms is an old story in bacteriology, but it is 

 only in quite recent years that it has been seen to have an 

 educational import for zoologists as well as for bacteria. 



Bacteria may be trained to use lactose or glycerol instead of 

 glucose as a source of carbon; nitrates instead of atmospheric 

 oxygen; ammonium salts instead of amino-acids as a source of 

 nitrogen; and so on. They may also be trained to resist anti- 

 biotics and other growth inhibitory agents to which they were 

 at first susceptible. 



The interpretation of the mechanism of these changes is 

 complicated by two facts: (a) bacteria are too small for it to be 

 possible to study their individual histories in sufficient detail, 

 so that the behaviour of individuals must be inferred from the 

 behaviour of bacterial populations; (6) the gene is not known 

 as a unit of segregation but only as a unit of mutation. The 

 modern analysis of recombination phenomena in viruses and 

 bacteria (Delbriick and Bailey, 1946; Tatum and Lederberg, 

 1947) will no doubt correct this second shortcoming in due 



102 



