80 FUNDAMENTAL STRUCTURE OF PROTOPLASM 



diseased cell, as electron micrographs seem to suggest, it becomes 

 hard to view them as organized invaders which multiplied within and 

 at the expense of the diseased cell. 



Besides myosin, a second protein, called actin, is extracted from 

 muscles ; this protein exists in a water solution in globular forms but 

 salt in high concentrations converts the particulate actin into a fibrous 

 form, which in turn is reverted to the globular form by removing 

 the salt by dialysis (82). Entirely the same phenomenon is observed 

 with Newcastle disease virus as stated above. Likewise with insulin 

 an analogous finding has been reported ; namely, this protein can be 

 converted into filaments with a width about 15 mju like tobacco-mosaic 

 virus, and this filaments again can aggregate into globular forms (83). 

 Lundgren (84) considered that filaments are produced by the unfolding 

 of globular proteins and the aligning of polypeptide chains. In addi- 

 tion, electron micrographs of myosin, actomyosin, tropomyosin, and 

 fibrin show that all these proteins have the common property to give 

 fibrils of varying length and thickness (85). 



The concept of the writer described thus far as regards the shape 

 and size of viruses is diagrammatically shown in Fig. 11. 



The ability of globular proteins to spread in the form of fibrils 

 or filaments is also fairly shown in the readiness with which proteins 

 spread and form the so-called surface films ; the spreading is especially 

 easily done in concentrated salt solutions and the film can be com- 

 pressed immediately after spreading and occupy the same area at the 

 point of minimum compressibility. Again, a change of potein called 

 denaturation is thought generally as an unfolding of globular proteins 

 into polypeptide chains. For example, it is reported that ovalbumin 

 when denaturated in the presence of urea becomes 500 to 700A in 

 length (86). 



An adequate system may be provided in the protoplasm for the 

 readily occurrence of such a reversible change, /. e. stretching and 

 shrinking, of the proteins. The majority of workers seem to pay 

 attention mainly to the elementary bodies in a stretching state, forming 

 the opinion that the protoplasm consists of fibrils, whilst others may 

 attach importance to the elementary bodies in a coagulated state, ad- 

 vancing the globular theories of protoplasm. Usually viruses are in 

 a coagulated state, but under certain environmental conditions they 

 may stretch themselves to form filaments. 



Sharp (87) has made studies on the "purified" virus of avian 

 erythro-myeloblastic leucosis under varying conditions of electron 

 micrography, and found that when preparations of the virus were 

 allowed to dry in the presence of salt, the particles exhibited extreme 

 pleomorphism, varying from filaments to sperm shapes, while the 



