ANIMAL VIRUSES 495 



preparations were homogeneous by e]ectrophoreti(;al and ulfcraccntrifugal 

 analysis (Shedlovsky et al., 1943). After degradation of the S component witli 

 chymotrypsin, the antigen formed needle-shaped crystalloids (Smadel et al, 

 1943), providing fm-ther evidence for the high degree of purity. The mole- 

 cular weight of the intact LS antigen, as determined by sedimentation and 

 diffusion, is 214,000; the axial ratio, 1 : 20 (Shedlovsky et al, 1943). 



Chemical analyses have shown that the LS antigen is a protein, having an 

 elementary composition of 15.8 % N and 50.6 % C. Tests for lipid, phos- 

 phorus, nucleic acid, and glucosamine were all negative. The antigen is 

 attacked by proteolytic enz}Tnes. Both the L and S parts may be destroyed 

 by papain, but chymotryjjsin under suitable conditions, will attack only 

 the S fraction, as already mentioned (Smadel et al., 1943). 



The hemagglutinin, according to studies with the preparative ultra- 

 centrifuge, is smaller than the infective particle, but larger than the LS anti- 

 gen (Chu, 1948a; Mayr, 1956). Assuming that it is approximately spherical, 

 the diameter is said to be 65 m/x, a density of 1.1 was estimated (Chu, 1948a). 

 Sufficient material for a detailed chemical analysis has not yet been prepared. 

 It is known, however, that the hemagglutinin can be precipitated with half- 

 saturated ammonium sulfate (Burnet, 1946), and destroyed by the a-toxin 

 of Clostridium welchii, as well as by cobra snake venom, both known to con- 

 tain lecithinase (Stone, 1946). These and some other observations have led 

 Burnet (1955a) to ascribe to it the character of a phospholipid-protein 

 complex. No enzyme corresponding to the neuraminidase of influenza virus 

 has been fomid associated with the vaccinia hemagglutinin. 



D. Summary (cf. Tables I and II) 



The chemical composition of the infective particles of animal viruses 

 seems to increase in complexity as the size of the particles increases. The 

 smallest particles contain only nucleic acid and protein. With increasing 

 size, one can find in addition lipid and sometimes carbohydrate; m the 

 largest, the vaccinia virus, one even finds copper, biotin, and a flavin-adenine- 

 dumcleotide,i.e., a coenzyme of the respiratory chain. 



The nucleic acid is sometimes RNA and sometimes DNA, but true animal 

 viruses unequivocally containing both types of nucleic acid are not known. 

 Past claims that both types are present in the same virus can probably be 

 attributed to impurities. A correlation between the size of the infective 

 particle and the type of nucleic acid does not exist. Thus, DNA is found in 

 the relatively smaU papilloma virus, as well as in the larger vaccinia virus. 

 Poliovirus, one of the smallest viruses known, and the much larger Newcastle 

 disease virus both possess RNA. However, differences are observed in the 

 VOL. I — 33 



