94 II. FUNDAMENTAL STRUCTURE OF PROTOPLASM 



For example, the yield of phage by Csaky et al, from 150 1. of 

 culture filtrate, was 60 mg, while by our method the same yield would 

 be easily raised from only one 1. Thus the yield by means of ultra- 

 centrifugations is of the order of one hundredth of that obtained by 

 our method, and only particles containing nucleic acids in rich amount 

 and lipids in poor are presumably separated as virus particles by the 

 ultracentrifugation. 



However, there is indeed a good reason for supposing that the 

 particles with high content of nucleic acid and therefore those with 

 high sedimentation rate are the virus particles with high activity, and 

 thus when the others have no or little activity such particles only can 

 reveal a high virus activity, the reason for which is discussed in 

 detail in the next Chapter. 



From what has been mentioned above it may be reasonable to 

 conclude that the high content of nucleic acids in virus particles 

 isolated by the ultracentrifugation is attributed to the separation of 

 particles with high sedimentation rate. There is, however, another 

 important reason for the high content of nucleic acids in virus parti- 

 cles. Gratia et al. (114), comparing the composition of the particles 

 obtained by the ultracentrifugation from tissue extracts of the silk 

 worm, infected with polyhedrosis virus, with those obtained from non- 

 infected worms, found that particles isolated from healthy silk worms 

 contained only ribonucleic acid, whereas the particles isolated from 

 infected worms contained, in addition, desoxyribonucleic acid. 



Moreover, it is generally recognized that bacteria infected with 

 phage synthesize much greater desoxyribonucleic acid than do normal 

 bacteria. Price (115) stated that normal staphylococci release neither 

 ribonuclec acid nor desoxyribonucleic acid into the mediurn, whereas 

 infected cells release both kinds of nucleic acids. Rafelson et al. (116) 

 found that the uptake of P^" by the minced, young mouse brain is 

 markedly stimulated by the in vitro infection and growth of Theiler's 

 virus in the minced tissue. They believed that the effect of the 

 virus on the P^^ uptake by the tissue may be explained by the in- 

 crease of ribonucleic acid synthesis in the infective tissue. Saenz and 

 Taylor (117) found a similar phenomenon with chick embryo and in- 

 fluenza virus. 



On the one hand cells infected with viruses are generally increased 

 in their propagating power. Even in the case of bacteria affected by 

 phage this is sometimes true as above stated. Thus, although bac- 

 terial cells are commonly subjected to lysis when affected by phage, a 

 proper amount of phage is occasionally capable of promoting the 

 proliferation of bacteria. On the other hand, as is generally accepted, 

 rapid propagation of cells is generally accompanied by the increase in 



