Discussion on “Ultra-microscopic viruses infecting animals and plants”

Abstract

I am much honoured by the suggestion of the officers that I should open this discussion, and I quite understand that the invitation is extended to me on account of my sympathy with these researches, and not on account of my achievements in them. I am to be followed by a number of gentleman who have extended the bounds of knowledge in many directions on which I shall touch, and you much look to them to contribute the real value to the debate. There is one side of the subject on which I have no first-hand information, and that is the side which concerns the virus diseases of plants. That does not matter, however, because I understand that I am to be followed by Prof. Murphy, who will make good all my deficiencies. I think it would have been more appropriate if Prof. Murphy had preceded me, firstly, because plants take precedence in the order of creation, and, secondly, because the first discovery of these filtrable viruses was the work of a botanist and concerned the disease of the tobacco plant. It was in 1892 that it occured to Iwanowsky (who had been looking for the cause of the mosaic disease of the tobacco plant and had failed to find any visible microbic agency which would account for it) to filter the juice of an infected plant through a porcelain filter. He found that the filtrate was infective for healthy plants in quantities as small as he could handle. The significance of Iwanowsky's observation was unappreciated until seven years later, when the fact was re-discovered by Beijerinck. In the meantime Loeffler and Frosch had discovered that foot-and-mouth disease was not due to any visible microbe but that the contagium was small enough to pass through a porcelain filter. This discovery was the accident of research. Their object was to separate contaminating microbes to see if there was a toxin formed in foot-and-mouth disease.