484 W. SCHAFER 



antibody. The question arose whether this is an integral part of the infective 

 particle; Smith and co-workers (Smith et al., 1953, 1955) beheve it is, since 

 the normal host-cell antigen and the 'normal' component of the influenza 

 virus are slightly different immunologically and also possess different thermal 

 stabilities. Furthermore they could show that there are also differences 

 between the 'normal' components of influenza A and B viruses. 



From quantitative studies, it has been determined that about 10 spherical 

 particles correspond to one JD^q in eggs (Isaacs and Donald, 1955; Donald 

 and Isaacs, 1954b). Since one can never completely prevent the inactivation 

 of infective particles by external influences and since the infectivity tests are 

 not so sensitive that every particle can cause an hifection, one can safely 

 assume that at least a large majority of the spherical units is identical with 

 the infective particles. 



According to our present knowledge, the purest preparations of infective 

 particles of influenza and fowl plague contain four main constituents: 

 nucleic acid, protein, lipid, and carbohydrate. 



Very probably RNA is the only nucleic acid present (Ada and Perry, 

 1954b; Frommhagen and Knight, 1956; Frisch-Niggemeyer and Hoyle, 1956; 

 Ada, 1957; Zillig et al, 1955; Schafer, 1957b). The small amount of DNA 

 (0.1 %) that recent studies, using microbiological tests (Miller, 1956), demon- 

 strated in influenza virus preparations may be due to impurities, although 

 Miller (1956) is not of this opinion. Reports on the RNA content of influenza 

 virus vary between 0.7 and 1 %, and for fowl plague virus between 1.8 (von 

 Zahn-UUmann, unpublished) and 4 %, corresponding to 1 molecule of M.W. 

 2 X 10® (Gierer, 1957) per infective particle of influenza and 1-3 molecides 

 per fowl plague virus. Chromatographic studies of the bases of different 

 strains of influenza virus have shown that differences exist in the base ratios 

 (Table I) of the A and B type viruses (Ada and Perry, 1955b, 1956); and 

 they are considered characteristic by Ada (1957). Thymine, the pyrimidine 

 base characteristic of DNA, was not found in any case. 



Uj) to this point the discussion has referred to virus preparations obtained 

 from infectious allantoic fluid. Ada (1957) has also studied the RNA compo- 

 sition of influenza virus preparations obtained from lungs of infected chick 

 embryos, where different base ratios were found. However, one must carefully 

 test the possibihty that these differences are due to host material impurities, 

 which could be present in larger quantities when tissue extracts are employ- 

 ed as the starting material. The lower specific activity (hemagglutinating 

 imits per milhgram dry weight) of the virus obtained from lung material, as 

 compared with the virus obtained from allantoic fluid, suggests such an 

 interpretation. 



The major percentage of the infective particles is protein in both viruses 

 (60-70 %) (Taylor, 1944; see Beard, 1948; Zillig et al, 1955). Amino acid 



