112 ir. FUNDAMENTAL STRUCTURE OF PROTOPLASM 



essential for the virus activity. Moreover, on studying the mammary 

 cancer of mice, Barnum and Huseby (163) have obtained by high-speed 

 centrifugation lipoprotein particles almost devoid of nucleic acid. These 

 particles possessed cancer-producing poteintialities which were equal to 

 the original nucleic acid containing preparation of the lactating gland. 

 Maaloe and Symonds (164) indicated that in both premature and ordinary 

 lysates of bacteria infected by phage there are non-infective particles 

 containing sulfur but no nucleic acid. These particles adsorb on 

 bacteria and precipitate w^ith antiserum in a way similar to typical 

 phage. However, they are somewhat lighter and have no appreciable 

 killing effect on bacteria. 



Price (165) has found that the activity of a phage preparation was 

 increased by 20 to 30 fold by the addition of nucleic acid. This fact 

 can be interpreted as indicating that some phage particles incapable 

 of developing the virus activity bacause of the looseness in their 

 structure acquire the rigidity on the combination with the nucleic 

 acid I with the revelation of the virus activity. The nucleic acid used 

 in this experiment was ribonucleic acid isolated from host bacteria or 

 yeasts, whereas the nucleic acid contained in phage preparations is 

 usually not ribonucleic but desoxyribonucleic acid which is regarded 

 by some workers as having the special relation to the virus. This 

 shows, however, that ribonucleic acid can contribute to the phage 

 activity like desoxyribonucleic acid. 



Bacteria infected with a phage are usually disintegrated into 

 minute particles which can be isolated by our isoelectric precipitation 

 method. It was found that only one out of 100 or 1,000 particles thiis 

 isolated shared the virus activity, and that as already described most 

 of the activity belonged to larger particles, smaller ones being un- 

 stable, most of which existing in non-infective state. This fact may 

 indicate that, even if nucleic acid Content was equal, larger particles 

 could develop the activity with more easiness than smaller ones. 

 However, since the distribution of nucleic acids in bacterial proto- 

 plasm is not uniform, each particle produced should be different in 

 nucleic acid content, and hence, even when the particles were equal 

 in size, only some particles with higher nucleic acid content would 

 be able to develop the virus activity. Furthermore, it may be 

 possible that some phage can exist in larger particles because of their 

 high content of nucleic acid which prevents the further decomposi- 

 tion of the particles into smaller ones. 



Anyhow, particles with high contents of nucleic acid may show 

 greater tendencies to act as viruses, and since such particles have 

 grea-ter sedimentation rates, only those sedimentable rapidly by ultra- 

 centrifugation would likely be regarded as the sole viruses. 



