The Cytoplasm as Specific Substrate 219 



E. CYTOPLASMIC HEREDITY OF THE PARTICULATE 

 TYPE (PLASMAGENES) 



The adherents of the theory of plasmagenes frequently go so far 

 as to speak of plasmagenes whenever cytoplasmic functions are in- 

 volved. Thus, as we shall see below, all plasmatic actions and differ- 

 entiations are made the work of plasmagenes, though there is not a 

 single fact which requires this assumption. The basis for such general- 

 izations is the idea that self-reproducing substances have to be 

 assumed in the cytoplasm. If a large protein molecule can be synthe- 

 sized only through a template mechanism, as is probable, every pro- 

 tein molecule might be called a plasmagene. In the interest of clear 

 notions and in order to avoid the danger of taking a suggestive termi- 

 nology for an explanation, we should speak of plasmagenes only when 

 a proved particulate, self-duplicating structure in the cytoplasm can 

 be shown to produce definite genie actions of the type known for the 

 genie material in the chromosomes. (Personally I should go still 

 farther and reserve the term "genie" and "genes" for chromosomal 

 material which can be analyzed by means of Mendelian behavior.) 

 But apart from what I consider rather wild and not helpful notions 

 about plasmagenes being involved in whatever the cytoplasm does, 

 there is a large body of facts, dealing with more or less certain par- 

 ticulates, as well as visible ones, in the cytoplasm, that have remark- 

 able genetic implications. It is this group of facts which is mainly 

 responsible for the past popularity of the idea of plasmagenes. 



a. Genoids 



L'Heritier and Teissier (1937, and many further papers; see 

 L'Heritier, 1951) discovered a remarkable set of facts relating to 

 C02-susceptibility in Drosophila. The main observations are these 

 (following L'Heritier, 1951). Ordinary flies can resist the gas for a 

 long time and recover at once from narcosis. Sensitive ones do not 

 recover; or, if they do, they are paralyzed. The seat of the latter effect 

 is the thoracic ganglion. The sensitivity is inherited by what appears 

 to be a cytoplasmic self-reproducing unit, which was called a 'gen- 

 oid." A normal fly can be made sensitive by transplantation of organs 

 taken from sensitives or by injection of an extract of sensitives. This 

 looks like the action of a virus. But the specific feature is that, once 

 in the Oiganism, the particle enters the germ track and is transmitted 

 to the offspring in a definite way. (This is known also for certain 

 parasites like the microsporidium of pebrine in the silkworm and 



