IX. VIRUSES AND NUCLEIC ACIDS 113 



The coli-phage particles isolated by our method contain nucleic 

 acids at the most only 15 per cent and even one third of the partix:le 

 is composed of lipids, whereas those isolated by ultracentrifugation 

 have been reported to contain so much nucleic acid as 40 per cent, or 

 more, and lipids only about 1 per cent (113). Moreover, the yield by 

 means of the ultracentrifuge is only of the order of one hundredth of 

 the yield by our method, and accordingly it is evident that particles 

 having a peculiar property ' only are to be obtained by ultracentrifu- 

 gation. Such peculiar particles would be able to act as the virus even 

 when other particles failed to do so. It must, however, be emphasized 

 that almost all the particles isolated by our method can sometimes 

 reveal phage activity when examined under most suitable conditions. 



Polyhedrosis virus, as already mentioned, is isolated, from poly- 

 hedral body, in needle shaped particles containing a large quantity 

 of desoxyribonucleic acid, but it has been reported that such particles 

 are contained in the polyhedral body only about 3 to 5 per cent ; the 

 most part of the body consists of proteins with a low phosphorus 

 content having no virus activity (33). 



The particles separated from normal, healthy plant leaves such as 

 those of tobacco and tomato have been reported to contain little or no 

 nucleic acid. The fact that they are so unstable as to be decomposed 

 by trypsin is apparently due to this scantiness of nucleic acid and 

 also to the high content of lipids. The probable reasons for the pre- 

 sence of nucleic acid in rich amount in the particles isolated from 

 infected leaves are already considered. Virus particles are commonly 

 not affected by proteolytic enzymes, indicating that the particles are 

 stronger in their structure than the enzymes. Living protoplasm is 

 likewise usually not affected by enzymes. However, when its regular 

 configuration is damaged to become unable to act as the assimilase it 

 may be called dead, and at the same time it will become digestable 

 by enzymes. Normal plant particles are presumably in this dead state 

 as their configuration would be disturbed severely during the prepar- 

 ing manipulation on account of their looseness in structure because of 

 the lack of nucleic acid and so they may be split by trypsin in contrast 

 to usual virus particles. 



Some bacteria produce agents termed haemolysins which act on 

 red blood cells to cause lysis. So far as our studies have reached, 

 haemolysins appear to exist in virus-like particles and also their action, 

 like that of viruses, consists in causing a disturbance in the proto- 

 plasm structure of blood cells. However, in contrast to viruses, 

 haemolysins fail to multiply. This is possibly due to their inability 

 to produce an exact replica in the protoplasm, that is, haemolysins 

 may cause only a structural disturbance instead of producing the 



