170 LIFE: ITS NATURE AND ORIGIN 



kappa, gene K mast be present if kappa is to be maintained and 

 multiplied in the cytoplasm, because if K is replaced by its allel k, 

 kappa disappears within a few cell divisions and the progeny become 

 permanently sensitive to paramecin. However, gene K cannot alone, 

 when introduced into a cell that has lost kappa, re-establish kappa 

 formation. But if a small amount of kappa is introduced into sensi- 

 tive KK stocks, then kappa is maintained and multiplied in all the 

 progeny. This Sonneborn terms "primer" action, and notes its 

 analogy to the finding of Cori in phosphorylase studies, that the pres- 

 ence of some glycogen is apparently necessary to the formation of 

 more glycogen. A reasonable but unproved explanation is that gene 

 K, modified by or under the influence of kappa, molds off or produces 

 something (molecule or molecular group) which serves as an enzyme, 

 or else that kappa forms a cytoplasmic catalyst, with some product of 

 K, the net result of the new catalyst area being the production of 

 paramecin and of kappa. 



The macronucleus of P. aurelia is a compound nucleus containing 

 at least 60 K genes. Several experimental methods indicate that about 

 250 kappa particles exist in the cytoplasm of a "killer" cell; but there 

 appears to be much less paramecin than kappa. The paramecin is 

 released into the medium very slowly, at any stage of the five-hour 

 fission life cycle. 



The rate of kappa multiplication varies in different stocks, and is 

 affected by conditions, temperature being important. When the 

 concentration of kappa is somewhat reduced experimentally, para- 

 mecin is no longer formed, but the cells remain resistant to its action. 

 Further reduction of kappa lowers resistance to paramecin; but as 

 long as a single particle of kappa remains in a cell containing gene K, 

 the concentration of kappa can be increased by appropriate conditions. 

 As kappa concentration increases, the sequence of phenotypic types 

 is reversed, sensitivity to paramecin disappears, and the cells become 

 resistant. With further increase in kappa concentration, production 

 of paramecin begins again. 



On cell division, kappa is unequally divided, and the studies of 

 J. R. Preer show that this inequality corresponds precisely to chance 

 or random distribution of kappa at the time of fission. Referring to 

 the differences found in the Dionne quintuplets by J. W. MacArthur, 9 

 J. Alexander stated: 10 "The slight differences found in monozygotic 

 twins do not seem to be due to the precisely duplicated genes, but 

 rather to inequalities in the apportionment of the zygote cytoplasm 

 upon mitosis, involving unequal distribution of catalyst modifiers 

 between the cells, which later develop into separate individuals." 

 Sonneborn points out that the concentration of kappa is of the order 

 of magnitude of one particle per 1,000 ^ 3 , which suggests that the 

 chemical laws of mass action, predicated upon probability calcula- 



