PHASES IN THE LIFE OF THE INDIVIDUAL 661 



of chromosomes in the nuclei of an egg (or of a tissue or organ) 

 to that of the surrounding protoplasm reaches a certain definite 

 limit, is regarded by Loeb ^ as evidence that this ratio is deter- 

 mined by the laws of mass action and chemical equilibrium. 

 He says further that if this conclusion is correct the synthesis 

 of nuclein compounds, from their protoplasmic constituents, 

 must be a reversible process. 



The fertilisation of an ovum is immediately succeeded by 

 an enormous synthesis of nijclear material. In the cellular 

 division which follows, each new nucleus is of the same size as 

 the parent nucleus. From this fact Loeb ^ concludes that the 

 nucleus itself, or one of its constituents, acts as a catalyser in the 

 synthesis of nuclein in the fertilised ovum. Eobertson,^ quoting 

 partly from Loeb, writes as follows : — " If the mass of the original 

 fertilisation-nucleus be m, the mass of nuclear material increases 

 during the first segmentation period to 2m, during the next to 

 4m, and so on in geometrical progression. The duration of the 

 various periods of segmentation, however, matters very little. 

 Hence in the first unit of time after the beginning of cell division, 

 a mass m of nuclear material is formed, in the second a mass 2m, 

 in the third a mass 4m, and so on ; thus the velocity of the 

 synthesis increases with lapse of time and with the mass of 

 nuclear material already formed. This is a characteristic of 

 that class of reactions known as autocatalytic, in which one of 

 the products of the reaction, or, in this case, one of the con- 

 stituents of the nucleus, accelerates the reaction. During the 

 process outlined above, an emphatic disproportion between 

 nuclear and protoplasmic material has been established. As 

 the nuclear synthesis becomes slower, however, the disproportion 

 tends to adjust itself until, finally, the growth of the organism 

 consists almost entirely of the growth of protoplasmic material 

 and in the final re-establishment of the equilibrium between 

 cytoplasm and nuclear material." 



Eobertson has investigated mathematically the quantitative 



^ Loeb, The Dynamics of Living Matter, New York, 1906. 



^ Loeb, " Weitere Beobaohtungen uber den Einfluss der Befruchtung," &c., 

 Bio. Chem. Zeitach., vol. ii., 1906. " The Chemical Character of the Process of 

 Fertilisation and its Bearing on the Theory of Life Phenomena," Seventh 

 Interuat. Congress, Boston, Vniv. of Galifomia Pviblications, vol. iii., 1907. 



' Robertson, toe. cit. 



