W. M. STANLEY 



organisms. Yet, when introduced into the cells of susceptible h(jsts, 

 these particles can direct or enter into the metabolic chain of events 

 of the cell. 



The rod-shaped anhydrous tobacco mosaic virus particle is 

 representative of a small group of viruses, but is certainly not repre- 

 sentative of all viruses, for most viruses that have been studied ade- 

 quately appear to be essentially spherical in shape and hydrated. 

 Among the viruses that have been obtained in essentially pure form and 

 studied in some detail are alfalfa mosaic virus with a diameter of about 

 17 m/i, tobacco ring spot virus with a diameter of about 19 m^u, tomato 

 bushy stunt virus with a diameter of about 26 m;u, equine encephalo- 

 myelitis and rabbit papilloma viruses with diameters near 40 m/i, 

 influenza virus with a diameter of about 100 m/x and vaccine virus 

 with a diameter of about 225 m/x. Of these, tomato bushy stunt virus 

 is the only one that has been obtained in crystalline form. This virus, 

 which contains about 17% nucleic acid, and about 83% protein, 

 crystallizes in the form of large, beautiful, rhombic dodecahedra. 

 The particles of bushy stunt virus appear to be strictly homogeneous 

 with respect to size, shape, and density; hence the case for regarding 

 these particles as molecules is as good as for any protein. 



The papilloma virus appears to be a nucleoprotein containing about 

 8% nucleic acid and little or no lipid. The particles of the equine 

 encephalomyelitis virus appear to be a liponucleoprotein complex 

 containing about 48% lipid, about 5% nucleic acid, and protein plus 

 a small amount of excess carbohydrate. Data on influenza virus 

 indicate that the 100 m/j, particle has a water content of about 60% 

 by weight, with the solid portion being composed of about 65% pro- 

 tein, about 25% lipid, about 7% carbohydrate, and a very small 

 amount of nucleic acid. Vaccine virus is the largest and most complex 

 virus that has been subjected to chemical investigation. The prepara- 

 tions were found to contain protein, lipid, carbohydrate, and thymus 

 nucleic acid in concentrations not materially different from those found 

 in bacterial cells. The vaccine virus preparations were also found to 

 contain phosphatase, catalase, lipase, biotin, riboflavin, flavin-adenine- 

 dinucleotide, and apparently significant and reproducible amounts 

 of copper. It is exceedingly difficult to prove that all of these repre- 

 sent integral components of vaccine virus, but it must be regarded as 

 significant that this large and complicated virus appears to retain 



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