The Cytoplasm as Specific Substrate 221 



the whole the facts recorded bear a striking similarity to the behavior 

 of lysogenic bacteria toward phage. 



The problem for our present discussion is whether the un- 

 doubtedly existing particles responsible for C02-sensitivity are viruses 

 with a definite behavior or are plasmagenes behaving like viruses. A 

 number of geneticists deny, a priori, a difference between genes and 

 viruses: such a problem does not exist for them. It must be realized 

 that for a long time the possibility has been discussed (see Buchner, 

 1953) that typical cellular inclusions like mitochondria are really sym- 

 bionts or were such originally. Such a view has been considerably 

 strengthened by the amazing facts on intracellular symbionts in in- 

 sects with specialized nutrition which Buchner and his school (see 

 1953 ) have revealed in a series of remarkable papers and books, show- 

 ing that these organisms of a yeast type supply the host organism with 

 basic biochemical substances which it cannot synthesize. These sym- 

 bionts are also transmitted in a specific way through the eggs. Of 

 course nobody would speak here of plasmagenes, but we might make 

 the point that such symbionts show one step in a process whereby 

 external organisms may become part of the cellular structure. A bril- 

 hant discussion of this point in terms of biochemistry and virology has 

 been presented by Lederberg (1952). We shall mention his con- 

 clusions later. 



At present such phylogenetic speculations are not very fruitful. 

 We may restrict ourselves therefore to the question whether the facts 

 which L'Heritier analyzed so beautifully can be interpreted as proving 

 a particulate cytoplasmic heredity. L'Heritier himself is very cautious, 

 though his term "genoid" indicates the interpretation he would prefer. 

 The facts seem to indicate to me the following. Different kinds of 

 viruses are known: for example, the crystallizable ones and the bac- 

 teriophages with a complicated organization. Also, different kinds of 

 substrates for virus reproduction are known: for example, ordinary 

 bacteria and lysogenic bacteria. The facts discovered by L'Heritier 

 show that the particles in question have all the important properties of 

 viruses. Certain puzzling details, like the different behavior of sperm 

 of different origin and the differences in propagation of the virus in in- 

 fected and hereditary carriers, seem to indicate specific features of the 

 cytoplasmic substrates. The apparent mutations may be described also 

 in terms of virulence and substrate changes. Therefore, it seems that 

 we are dealing with an infectious virus of special properties and sub- 

 strate relations, which are extremely interesting, especially because the 



