PHYSICS OF SEGMENTATION. IOI 



segmentation are to be put into the above classes, but also, with 

 the addition of the class, surface energy, which is of special im- 

 portance here, the phenomena taking place within the cell itself, 

 preceding and during cleavage. We accordingly consider the 

 cell to be a physico-chemical object, whatever else it may be, and 

 subject therefore to general physical principles. The special na- 

 ture of the physical processes that occur in it is to be demon- 

 strated by showing that the effectiveness of the physical methods 

 used for causing segmentation implies that, or at least can be ex- 

 plained, if by each method only one and the same series of events 

 is made to take place. The bringing together of results in this 

 way exemplifies what we have termed synthesis, and the internal 

 agreement with which it is identical makes for the probable cor- 

 rectness of our theory. 



2. GENERAL PHYSICAL PRINCIPLES TO BE OBSERVED IN THE 

 INTERPRETATION OF THESE DAT A. 1 



If the energies both within and without the cell belong to the 

 classes named, we must in our endeavor to get at the meaning of 

 the data at hand be guided strictly by the most general funda- 

 mental chemical and physical principles valid for those. These 

 principles, some of which are of course well known, may be 

 stated as follows : 



I. The " first law " of energetics, that of the conservation of 

 energy. This is considered to have an experimental basis in the 

 fact that, e. g., a weight of one kilogram falling 424 mecers raises 

 the temperature of one kilogram of water I C. as indicated on 

 an arbitrarily selected scale. This is interpreted to mean that 

 the kinetic energy of the falling body is quantitatively equal to 

 the heat energy gained in the rise in temperature. However this 

 cannot be strictly proven, for the two energies are qualitatively 

 different, and have no common factor. It would therefore be 



1 The principles as stated are to be found in no one author, but are with their criticism 

 the result of the study of the works of Planck, Mach, Ostwald, Helm, Wald, Riecke, 

 and others; some of these are as follows: Planck, " Prin. d. Erh. d. Energie " ; 

 Ostwald, " Vorlesungen iiber Naturphilosophie," " Allgemeine Chemie," and other 

 writings; Helm, " Die Energetik nach ihrer gesch. Entw. " ; Rankine, Philos. Alag., 

 1867 (4); Mach, " History of Mechanics," " Warmelehre," "Pop. Lect," "An- 

 alyse der Empf" ; Riecke, " Lehrbuch d. Physik." 



