Natural selection—survival of the fittest—is as old as life itself. Applied genetics which is purposeful in contrast to natural selection also has a long history, particularly in agriculture; it has received impetus from the more exacting demands of the food industry for animal breeds with higher lean : fat and meat : bone ratios, for crops resistant to the teeming world of parasites. Capturing the exquisite scent, the colours and form beautiful of a rose is in effect applied genetics and it has even been applied to man. For example, Frederick the Great, Emperor of Prussia, to maintain a supply of very tall men for his guards—his Prussian Guards averaged seven feet in height—ordered them to marry very tall women to produce offspring carrying the genes of great height. In recent times, however, research and experiment in genetic control, more in the nature of active interference with genetic composition, has developed sufficiently to begin yielding results. It is self‐evident that in the field of micro‐organisms, active interference or manipulations will produce greater knowledge and understanding of the gene actions than in any other field or by any other techniques. The phenomenon of “transferred drug resistance”, the multi‐factorial resistance, of a chemical nature, transferred from one species of micro‐organisms to another, from animal to human pathogens, its role in mainly intestinal pathology and the serious hazards which have arisen from it; all this has led to an intensive study of plasmids and their mode of transmission. The work of the Agricultural Research Council's biologists (reported elsewhere in this issue) in relation to nitrogen‐fixing genes and transfer from one organism able to fix nitrogen to another not previously having this ability, illustrates the extreme importance of this new field. Disease susceptibility, the inhibition of invasiveness which can be acquired by relatively “silent” micro‐organisms, a better understanding of virulence and the possible “disarming” of organisms, particularly those of particular virulence to vulnerable groups. Perhaps this is looking for too much too soon, but Escherichia coli would seem to offer more scope for genetic experiments than most; it has serotypes of much variability and viability; and its life and labours in the human intestine have assumed considerable importance in recent years. The virulence of a few of its serotypes constitute an important field in food epidemiology. Their capacity to transfer plasmids—anent transfer of drug resistance— to strains of other organisms resident in the intestines, emphasizes the need for close study, with safeguards.
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