Methods for the purification of tomato bushy stunt and tobacco mosaic viruses

Since we first described methods for making liquid crystalline preparations of tobacco mosaic virus [Bawden & Pirie, 1937] and crystalline preparations of tomato bushy stunt virus [Bawden & Pirie, 1938], we have made preparations of both viruses by many other methods. As a result, we can now describe simpler and better procedures. Other workers have used differential ultracentrifugation; because of the infrequency with which stable substances of high molecular weight seem to occur in normal leaves, this method of preparation is undoubtedly of great value. The handling of large volumes of sap in the ultracentrifuge, however, is laborious, and many laboratories where plant viruses are studied do not have this equipment. Methods of preparation that are trustworthy and involve only ordinary centrifuges may therefore be of more general use.