Wendell M. Stanley and Journal ul ttiuluyicul Vhemiatry 



BETWEEN LIVING AND NOT-LIVING 



Seen through an electron microscope (right), tobacco-mosaic virus suggests "microbes". 

 Yet it seems to have definite chemical composition, since it crystallizes like a non- 

 living salt (left), although, like living protoplasm, it is able to assimilate foreign matter 



this group of diseases are hoof-and- mouth disease of cattle, yellow fever, small- 

 pox, measles, mumps, influenza, encephalitis, infantile paralysis, and the so- 

 called mosaic diseases of tobacco and other plants. 



Like living bacteria, a virus may increase in quantity by feeding at the 

 expense of other substances — in the case of the mosaic diseases, the materials 

 of a living plant or animal body. A virus thus grows and reproduces itself, 

 becoming more and more. In some respects, however, a virus behaves like a 

 large molecule of protein. It has no discoverable structure, such as the simplest 

 of plants and animals have. A virus seems thus to be a distinct chemical sub- 

 stance which may form crystals, and may conceivably arise without the 

 previous action of life. And yet such a substance shares some of the charac- 

 teristics of living matter. 



In 1918, the Canadian Felix d'Herelle (1873- ), a bacteriologist, 

 started an investigation on just what happens to overcome the living bac- 

 teria when a person recovers from dysentery. D'Herelle separated out a 

 substance that destroys and actually dissolves the bacteria. He called this 

 something bacteriophage — that is, "bacteria-eater". Unlike the antibodies 

 formed in an organism reacting to bacterial infections (see pp. 232-234), 

 bacteriophage can increase in quantity outside the body of the host. 

 D'Herelle, and later others, fed masses of bacteria to bacteriophage in glass 

 dishes and so increased the quantity of the substance. 



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