STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 27 



application of visible light to the complex of cell and damaged virus and not 

 to the free virus alone (Dulbecco, 1950). Most recently, Rupert et al. (1958) 

 have described the increase of activity obtained when an ultraviolet- 

 inactivated transformation agent (DNA) derived from HemopJiilus influenzae 

 was treated with visible Hght in the presence of an extract of E. coli strain B. 



D. On the Origin a7id Cellular Relations of the Viruses. 



It is possible to imagine that many viruses are degenerate microorganisms 

 and, indeed, that their composition and life cycle reflect such a development. 

 For example, vaccmia virus may be thought of in this way. The virus seems 

 to contain a number of units capable of metabolic activity (flavin adenine 

 dinucleotide, biotin, copper) and it might be supposed, among many possi- 

 bihties, either that these are evolutionary vestiges of a once extensive 

 metaboHsm or that the metaboHsm still exists, but that the biochemists have 

 not sought the proper reactivities. Although this virus contains DNA alone, 

 a nuclear constituent, the DNA of the virus ajDpears to be deposited when 

 the particle is in the cytoplasm. Since the host cell lays down its DNA in its 

 nucleus (suggesting a nuclear locaUzation for the enzymes involved in this 

 synthesis) and some DNA-containing insect viruses do appear to be formed 

 witliin the chromatin of the infected cell (Smith, 1954), the mode of synthesis 

 of DNA in vaccinia virus suggests the possibihty that this virus may possess 

 its own enzyme for such a synthetic achievement. Although it has been 

 reported that the development of vaccinia virus has an eclipse phase, as do 

 the phages, it can be imagined that the virus is masked temporarily, and that 

 we do not know how to demonstrate the complete active particles which may 

 be present. However, that there is a basic dissimilarity in the multiplication 

 of vaccinia virus and true cells is suggested by the electron micrography of 

 vaccinia-infected ceUs, in which the sections seem to reveal immature par- 

 ticles consisting of apparently empty external membranes and do not expose 

 intact dividing particles (Morgan et ah, 1954). 



On the other hand, it is considered to be quite significant that aU the 

 phages contain DNA alone, that phage infection demonstrably produces 

 effects to a greater or lesser degree on bacterial nuclei and chromatm, and, 

 in the case of lysogenic systems, the prophages exist and multiply in close 

 association with a bacterial chromosome. As noted above, a similar situation 

 may exist in the multiplication of many insect viruses. Data of this type 

 represent perhaps the strongest evidence to suggest that many viruses are 

 abberrant cellular particulates, abberrancies produced by a mutation in 

 polymer synthesis, which confers a selective advantage on the mutated 

 polymer at the expense of the development of normal polymers and parti- 

 culates. In this context, one might ask if the plant viruses are the colorless 



