ON SOME PHYSICAL MANIFESTATIONS OF LIFE 6 1 



have thought of the possibility that the continuation of the synthetical 

 process which leads to the formation of nuclear material from certain 

 constituents of the protoplasm gives rise to the formation of astrospheres 

 as soon as the maximal growth of the chromosomes is reached. But 

 this does not need to enter into our consideration for the present. 



Since each daughter nucleus of a dividing blastomere has the same 

 number of chromosomes as the original nucleus of the egg, it is clear 

 that in a normally fertilized egg each nucleus has twice the mass of 

 chromosomes as the nucleus of a merogonic egg, i.e. an enucleated frag- 

 ment of protoplasm which has only the sperm nucleus. Boveri has 

 not only ascertained this fact but he has also ascertained the further fact 

 that the final size of the cells after the cell divisions have come to a 

 standstill is always in proportion to the original mass of the chromatin 

 contained in the egg ; the cells of the merogonic embryo, e.g. the mesen- 

 chyme cells, are only half the size of the same cells in the normally 

 fertilized embryo. Driesch has just furnished a further proof of Boveri's 

 law, that the final ratio of the mass of the chromatin substance in a 

 nucleus to the mass of protoplasm is a constant in a given species. 

 He compared the size of the mesenchyme cells in a sea-urchin embryo 

 produced by artificial parthenogenesis with those of a normally fertilized 

 egg and found them half of the size of the latter. When the fertilized 

 eggs and the parthenogenetic eggs are equal in size from the start, — 

 which is practically the case if eggs of the same female are used, — the 

 process of the formation of mesenchyme cells comes to a standstill in 

 the normally fertilized eggs when the number of mesenchyme cells is 

 half as large as the final number of mesenchyme cells found in the 

 parthenogenetic egg.* As a matter of fact, Boveri's results as well as 

 those of Driesch were obtained by counting the cells formed by eggs 

 of equal size and not by only measuring the size of the cells. It is 

 most remarkable that certain apparent exceptions to Boveri's law 

 which Driesch has actually found have been predicted by Boveri. 



The fact that the process of cell division comes to a standstill when 

 the ratio of the mass of the chromosomes in the nuclei of an egg or an 

 organ to that of the surrounding protoplasm reaches a certain limit, 

 suggests- in my opinion the possibility that this ratio is determined by 

 the laws of mass action and chemical equihbrium. If this is correct, 

 the synthesis of nuclein compounds from the protoplasmic constituents 

 must be a reversible process. This suggestion would gain in probabihty 

 if it could be shown that a reduction of size in protoplasm in the case of 

 starvation is also followed or accompanied by a reduction in the size 

 of the nuclei. 



* Driesch, Archiv fur Entwickelungsmechanik, Vol. 19, p. 648, 1905. 



