338 



THE AMERICAN NATURALIST [Vol. LI 



action has been made independently by a number of in- 

 vestigators.^^ It will be perceived that on the basis of 

 the foregoing theory of autocatalysis, this suggestion 

 becomes closely allied to the familiar and ancient com- 

 parison of vital growth to the growth of a crystal. The 

 customary objection to this comparison, viz., that a crys- 

 tal grows by accretion whereas protoplasm increases by 

 intussusception, loses its force as soon as we regard liv- 

 ing matter as a complex mixture of substances suspended 

 by colloidal subdivision in water, since there is no evi- 

 dence that the individual colloidal particles do not grow 

 by accretion. On the contrary, it is almost inconceivable 

 that these bodies, which are the real chemical units of pro- 

 toplasm, should grow in any other way. The growth of 

 a system like a cell could be regarded as the resultant 

 effect of a very large number of component growths, each 

 governed by its specific autocatalytic mechanism. It has 

 been shown by T. B. Eobertson^*' that growth curves, with 

 respect to the time, actually do coincide in general form 

 with the curve characteristic of an autocatalytic reaction. 



A multitude of observations substantiate the belief that 

 the internal determination of cell-life rests primarily with 

 the nucleus,^' or with the chromatin substance of the cell, 

 when no well-defined nucleus is present. Even in the 

 highly organized cell, this substance can be seen to pos- 

 sess a mosaic structure, and it can be shown that for a 

 given species this structure is sensibly constant,^^ so that 

 it is necessary to suppose that a reduplication of chromatin 

 units occurs with each cell-division. This process of re- 

 duplication is apparently made visible to us in mitosis. 



35 See, for example, Ostwald, W., "Ueber die zeitlichen Eigenschaften der 

 mechanik des Organismus, herausgegeben von W. Eoiix (1908), Heft 5, 

 Leipzig. lEt fG th f I T •] 1 d 



its Biochemical Significance," Archiv fiir Entwicklungsmechanik (1908), 25, 

 581-615; and subsequent articles in the same journal. 



37 See Wilson, E. B., "The Cell in Development and Inheritance," second 

 edition, revised (1911), 30-31, 341-354. 



38 Cf. Boveri 's Individualitats Sypothese and ' ' law of proportional nuclear 

 growth." 



