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Abstract Tobacco mosaic was the first disease shown to be caused by a filter-passing virus, and Beijerinck (1898) suggested as its cause a “contagium vivum fluidum", Since then many other theories have been advanced, but there has been little positive evidence to indicate whether the virus more nearly resembled organisms such as small bacteria or chemical molecules such as the larger proteins. Recently, however, Stanley has isolated from tobacco (1936a) and tomato (Stanley and Loring 1936) plants suffering from mosaic a protein which he describes as crystalline and as possessing the properties of the virus. When susceptible plants were inoculated with this protein at a dilution of 10-9 they developed typical symptoms of the disease. The protein was obtained from infective sap by repeated precipitation with 40% saturated ammonium sulphate solution, and by adsorption on and washing from celite. The “crystals” described by Stanley were small needles produced by precipitation with acid ammonium sulphate. A number of statements in Stanley’s earlier paper (1935 more especially those dealing with the nitrogen content and the serological activity, made us doubt the purity of his product, and preliminary experiments with methods similar to those used for the preparation of suspensions of potato virus “X” (Bawden and Pirie 1936) gave us products with much higher precipitation end-points with antisera than those claimed by Stanley. We have now exchanged material with Dr. Stanley and find no gross differences in the activities of our respective products. We have found, however, that by further purification the protein in neutral solution can be obtained in liquid crystalline states. Also, as will be shown later, there are considerable differences in the chemical descriptions given of the virus protein; some of these differences have already been resolved, and others presumably will be by future work.
Bawden et al. (Tue,) studied this question.