478 W. SCHAFER 



could be breakdown products of infective particles; and third, tliey may be 

 side products of abnormal virus synthesis. 



On the other hand, it is well known that the filamentous forms arise as 

 surface protrusions of the infected cells. Some diversity of opinion exists, 

 however, as to whether or not the spherical infective particles are jDroduced 

 from them. 



III. Problems and Methods of Chemical Analysis 



The chemical studies of the various particles are directed, first, toward 

 a quahtative and quantitative determination of the main constituents, 

 followed by a more precise analysis of their chemical composition, e.g., 

 amino acid analysis of the proteins. 



This can now be accomplished with relatively small amomits of virus 

 material, by using several sensitive and accurate analytic methods, such as 

 spectrophotometry and paper chromatography. A discussion of the various 

 analytical procedures is not within the scope of this chapter. In carrying out 

 such studies it should be kept in mind that some fractions may consist of 

 more than one component. Thus, the protein fraction can be composed of 

 different proteins, as suggested by the fact that some animal viruses possess 

 several antigens. A similar situation may hold for the nucleic acid of the 

 larger viruses. 



Only a few virus particles are needed for a method developed by Dawson 

 and McFarlane (1948) to study their chemical composition. In this procedure, 

 the virus is incubated with enzymes after some appropriate pretreatment and 

 then is observed in the electron microscope to see if any degradation has occurred . 



The main application of this method is to localize the individual chemical 

 components m the virus particle. Frequently, serological studies can deter- 

 mine whether an antigenicaUy active component is located on the surface of 

 the particle. X-ray crystallographic analyses can also be made, since two 

 animal viruses have been crystallized (Schaffer and Schwerdt, 1955a; Mattern 

 and Du Buy, 1956). One of the most important advances in this direc- 

 tion would be obtained with the development of electron optical staining 

 techniques. 



In looking for biochemical activities associated with the virus particle, one 

 is especially interested in enzymes. Here, it should be borne in mind that 

 virus enzymes can possess activities not previously known; one good example 

 is the enzyme found in influenza virus (see Gottschalk, 1957). Actually, only 

 one animal virus has been extensively studied with respect to different sorts 

 of enzymes (see Smadel and Hoagland, 1942). 



When the chemical components of the various virus-specific particles have 

 been identified, the way is prepared for studies concerning their origin and 



