ON SOME PHYSICAL MANIFESTATIONS OF LIFE 59 



which result in the division of the nucleus and the cell. It had been 

 tacitly recognized by botanists that the growth of a cell precedes its 

 division and is possibly the cause of the division. The botanist J. Sachs 

 was the first to definitely state that in each species the ultimate size of 

 a cell is a constant for each organ, and that two individuals of the same 

 species but of different size differ in regard to the number, but not in 

 regard to the size of their cells.* Amelung, a pupil of Sachs, determined 

 the correctness of Sachs's theory by actual counts. Sachs, in addition, 

 recognized that wherever there were large masses of protoplasm, e.g. 

 in Siphonese and other cceloblasts, many nuclei were scattered throughout 

 the protoplasm. He inferred from this that "each nucleus is only 

 able to gather around itself and control a limited mass of protoplasm." f 

 He points out that in the case of the animal egg the reserve material 

 - fat granules, proteins, and carbohydrates are partly transformed 

 into the chromatin substances of the nuclei, and that the cell division 

 of the egg results in the cells reaching that final size in which each 

 nucleus has gathered around itself that mass of protoplasm which it is 

 able to control. Morgan J and Driesch tested and confirmed the idea 

 of Sachs for the eggs of Echinoderms. Driesch produced artificially 

 larvae of sea urchins of one eighth, one fourth, and one half their normal 

 size by isolating a single cleavage cell in one of the first stages of seg- 

 mentation of the fertilized sea-urchin egg. He counted in each of the 

 dwarf gastrulse resulting from these partial eggs the number of mesen- 

 chyme cells and found that the larvae from a ^ blastomere possessed 

 only , those from a \ blastomere only ^, and those from a | blasto- 

 mere only of the number of cells which a normal larva developing 

 from a whole egg possessed. Moreover, he could show that when two 

 eggs were caused to fuse so as to produce a single larva of double 

 size, the gastrulas of such larvae had twice the number of mesenchyme 

 cells. Driesch drew from his observations the conclusion that each 

 morphogenetic process in an egg reaches its natural end when the cells 

 formed in the process have reached their final size. 



Gerassimowll found that by exposing dividing cells of Spirogyra 

 to a low temperature the division became irregular, and it happened 

 that the nuclear material instead of being divided between the two 



* T- v. Sachs, " Physiologische Notizen," VI, Flora, 1893. 

 t Sachs, " Phvsiologische Notizen," IX, p. 425, Flora, 1895. 



mechanik 



Vol 



XVI, 1 903. 



Driesch, "Von der Beendigung morphogener Elementarprocesse," Arch, fur Enhvicke- 

 Inng'smechanik, Vol. VI, 1898. "Die isolirten Blastomeren des Echinidenkeims," ibid., Vol. 

 X, 1900. 



|| Gerassimow, Zeitsch.fur allgemeine Physiologic, Vol. I, p. 22O, 1902. 



