ANIMAL VIRUSES 489 



(Ada and Perry, 1955a, 1956; Paucker et al., 1956). The content of G antigen 

 in this material behaved m a similar fashion; this was to be expected, since 

 G antigen is the carrier of the BNA in the infective particle (Lief and Henle, 

 1956c). According to Ada and Perry (1956), the KNA content of preparations 

 of incomplete forms can decrease to about 0.3 % (dry weight percentage). 

 From his results, Ada (1957) came to the conclusion that the incomplete 

 forms of influenza isolated from allantoic fluid are not uniform with respect 

 to their nucleic acid content. No differences in the nucleic acid composition, 

 compared with that of the infective particles, were detectable (Ada and 

 Perry, 1956) (see Table I). In contrast to the nucleic acid content, the 

 amount of lipids is higher in the incomplete forms than in the infective 

 particles. This was suggested by experiments using P^^-labeled material 

 (Paucker et al., 1956). The label in the alcohol-soluble fraction increased 

 with increasing degrees of mcompleteness. Uliler and Gard (1954) showed 

 that substances soluble in ethanol and ethyl ether amounted to 54 % in 

 incomplete forms from allantoic fluid. 



Incomplete forms from infected tissues were investigated in fowl plague. 

 Some 50-60 % lipid was found in preparations w^hich possessed a high degree 

 of purity (Schafer, 1955a). Thus, it seems likely that a common characteristic 

 of the incomplete forms of influenza and fowl plague is a relatively high 

 lipid content, up to twice the percentage found in the infective particles. 

 Glucose-6-phosphatase has also been demonstrated to be associated with 

 preparations of the incomplete forms of fowl plague virus, but it is not yet 

 clear whether this is an intrinsic component (Schafer, 1957a). 



The filamentous forms of influenza and fowl plague have scarcely been 

 studied chemically. By treatment with enzymes, however, it has been shown 

 that the filamentous particle of influenza is mostly trypsin-sensitive (Valen- 

 tine and Isaacs, 1957a); consequently, it would seem to consist mainly of 

 protein. Most agents capable of lysing red blood cells destroy the filaments. 

 This led Burnet (1956) to conclude that the surface of filamentous forms has 

 properties similar to those of the cell surface. 



2. Newcastle Disease Virus 



The Newcastle disease virus (NDV), which also belongs to the myxovirus 

 group, is considerably larger than influenza and fowl plague virus. The 

 flattened romid particles, seen only under appropriate conditions in the 

 electron microscope, have a highly variable diameter with an average value 

 of 150 to 190 m/x (Elford et al, 1948; Bang, 1948; Schafer et al, 1949). 

 From 5 to 7 particles of this sort are needed for one ID50 in eggs (Bang, 1948 ; 

 Isaacs and Donald, 1955). The particles change their form in solutions of 

 higher salt concentration, without loss in infectivity. After such treatment 



