490 W. SCHAFER 



one sees mostly extended forms. The teckniques already described for 

 influenza and fowl plague are also suitable for tlie purification of this agent. 



The chemical composition of the hifective particles of NDV seems to be 

 similar to that of the myxoviruses previously discussed. Older studies (Cunha 

 et al., 1947; see Beard, 1948) have demonstrated the presence of '^ 65 % 

 protein, /--^ 4 % nucleic acid, '-^ 7 % carbohydrate glucose equivalents, and 

 '--' 27 % lipid, mostly phospholipid; 3.5 % RNA was found, as well as 0.61 % 

 DNA. However, these investigations were carried out on preparations purified 

 solely by ultracentrifugation and which, according to serological investiga- 

 tions, contain a large quantity of normal component (Muiik and Schafer, 

 1951). Recently, studies have been made on small amounts of carefully 

 purified NDV which had been labeled with P^^ (Franklm et al, 1957). These 

 showed that probably only one nucleic acid type is present m NDV, namely, 

 RNA. The R.NA is arranged on a ringlike structure that is surrounded by a 

 trypsin-sensitive shell (Valentine and Isaacs, 1957b). In contrast, the phos- 

 pholipid seems to be superficially situated, since it can be degraded by treat- 

 ment with phospholipase. Since the degradation is associated with a loss of 

 infectivity this fraction must be necessary to the particle (Franklin et al. 

 1957). 



NDV possesses not only a receptor-destroying activity but also the ability 

 to lyse red cells (Traub and Miehler, 1946; Kilham, 1949 ; Burnet and 

 Lind, 1950). Burnet (1955b) considers that "hemolysis is due to enzymatic 

 action going beyond the normal type of receptor destruction." Detailed 

 studies are not available. 



It is not yet known w^hether an S antigen occurs in NDV-infected tissues. 

 Incomplete and filamentous forms are present but have not been chemically 

 analysed. 



3. Virus of Avian Myelohlastic Leukosis 



The agent of avian myeloblastic leukosis, is morphologically very similar 

 to NDV (see Beard et al., 1955; see Beard, 1956). Large quantities of the virus 

 ('^ 1.5 mg./ml.) are present in the plasma of certain diseased chickens. 



Although detailed chemical studies have not been made on this agent, it is 

 mentioned here because an adenosinetriphosphatase (ATPase) is associated 

 with it. The following observations suggest that the enzyme is coupled with 

 the virus particle: (a) the enzyme and the specific particle appear progressively 

 in the chick plasma with the development of the disease; (b) they cannot be 

 separated from each other by electrophoresis or by ultracentrifugation; 

 (c) they are precipitated together by antiviral serum. 



But this behavior does not prove conclusively that the ATPase is actually 

 an intrinsic part of the virus, because it could also be due to an enzyme 



