IX. VIRUSES AND NUCLEIC ACIDS 115 



cytosine; viral DNA increases and bacterial DNA is destroyed in in- 

 fected bacteria (169). Again, it has been found that the DNA of cer- 

 tain strains of phage contains no cytosine ; instead, they contain a 

 hitherto unrecognized pyrimidine, while other viruses contain no this 

 pyrimidine (170). 



Since the structure of a nucleic acid polymer may be rigid, even 

 when some virus-like particles, or elementary bodies of protoplasm, 

 consist mostly of nucleic acids, only a small particle being proteins, 

 the specific pattern may exist unimpared in the particles. In an ex- 

 treme case where all the protein molecules are eliminated, particles 

 thus consisting of nucleic acid only may not be impossible still to 

 retain the pattern to act as the template. There seems to be an 

 evidence that this may be possible as mentioned in the next Part. 



As regards nucleic acids there are still many other problems to be 

 discussed, but they will be reserved for Part IV where the nature of 

 genes is to be considered in detail. 



