124 



THE CELL AND PROTOPLASM 



upon the virus and the host, some viruses 

 occurring in amounts as great as a part 

 per 200 and others iij amounts as small as 

 a part per million, with the possibility that 

 other viruses may occur in still smaller 

 amounts. In those cases where it has been 

 found impossible to isolate weighable 

 amounts of virus, or to demonstrate the 

 presence of virus by immunological reac- 

 tions, it is possible that the virus was ex- 

 tremely unstable or existed in such great 

 dilution that it escaped detection by means 

 other than activity measurements. The 

 purified preparations of the various viruses, 

 such as latent mosaic, tobacco ring spot, 

 bushy stunt of tomato, and the Shope 

 rabbit papilloma viruses, and a staphylo- 

 coccus bacteriophage, have been found to 

 have quite different and highly character- 

 istic chemical, physical, and serological 

 properties. It may be concluded, therefore, 

 that the different viruses, as well as the 

 various strains of a given virus, reach 

 widely different concentrations in their 

 hosts, and that the respective purified prep- 

 arations possess definite and highly charac- 

 teristic chemical, physical, and serological 

 properties which may be correlated with 

 the biological or virus activity. 



The purified viruses that have been iso- 

 lated have been found to consist largely of 

 protein which is susceptible to digestion 

 with certain proteolytic enzymes and which 

 may be denatured by appropriate treat- 

 ment. In every instance so far studied, 

 the digestion or denaturation of the protein 

 has been accompanied by the loss of virus 

 activity and, in general, the rate of diges- 

 tion or of denaturation and the rate of loss 

 of activity have paralleled each other, al- 

 though in certain instances the inactivation 

 reaction was somewhat the more rapid of 

 the two. The studies have included denatu- 

 ration by acid, alkali, heat, dodecyl sulfate, 

 urea, etc. It should be noted that the puri- 

 fied preparations of the different viruses 

 were found to be stable only over certain 

 ranges of hydrogen-ion concentration which 

 were definite and characteristic for each 

 virus. In most instances, at the same pH 

 that caused loss of activity, there occurred 



a break-up of high-molecular-weight ma- 

 terial that could be demonstrated by means 

 of the analytical ultracentrifuge. It has 

 also been found possible to inactivate some 

 virus preparations, such as those of tobacco 

 mosaic, cucumber mosaics 3 and 4, and la- 

 tent mosaic, with nitrous acid, hydrogen 

 peroxide, formaldehyde, or ultraviolet 

 light without the accompanying gross 

 change in properties that is usually re- 

 ferred to as denaturation. The general 

 chemical, physical, and serological proper- 

 ties of the inactivated preparations are very 

 similar to those of active preparations. 

 For example, in the case of tobacco mosaic 

 the preparation still consists of a high- 

 molecular-weight nucleoprotein which may 

 be crystallized and which reacts specifically 

 with antiserum to active virus. Should it 

 prove possible to inactivate a virus with 

 but a very slight change in its makeup, it 

 is possible that very sensitive chemical or 

 physical tests might be necessary in order 

 to detect the change. However, despite the 

 great similarity in general properties, in 

 every case yet studied it has been possible 

 to demonstrate that the inactivation was 

 accompanied by a measurable change in 

 one or more of the chemical, physical, or 

 serological properties of the preparation. 

 In the treatment of tobacco-mosaic virus 

 with formaldehyde, the inactivation was ac- 

 companied by a decrease in amino nitrogen 

 as measured colorimetrically or by means 

 of the Van Slyke gasometric method, and 

 by a decrease in the color developed by 

 Folin's phenol reagent. Of considerable 

 importance in connection with the correla- 

 tion of chemical with biological properties 

 are the facts that it w^as found possible to 

 reactivate the formolized virus, and to dem- 

 onstrate that the reactivation was ac- 

 companied by an increase in amino nitro- 

 gen, as measured by the color developed 

 with ninhydrin, and also by an increase in 

 the color developed with the phenol rea- 

 gent. This correlation indicates that the 

 virus activity is a property of the nucleo- 

 protein and provides information concern- 

 ing the structure necessary for activity. 

 The action of 36 per cent urea in 0.1 M 



