302 E. G. Spaulding 



on one side of which the strengths of the sugar solution would per- 

 mit segmentation to take place, on the other side, not; and that by 

 repetition of this procedure with more finely graded solutions, this 

 inhibition point could gradually be fairly definitely determined for 

 each of the successive cleavages. This procedure was carried out 

 by six successive experiments, with results which agreed so closely 

 that further determinations seemed not to be necessary, even had 

 the failure of material not made them impossible. The results, 

 too, confirmed the hypothesis that for the inhibition of each suc- 

 cessive segmentation a lower pressure was required than for the 

 preceding. The numerical value thus obtained for any two such 

 pressures before and after a cleavage, since each pressure is a meas- 

 ure of the opposed resultant pressure from within, gives the basis 

 for the computation of the energy-transfer involved in that cleavage. 

 It is evident, then, that the egg is here regarded as a system in 

 which, acting from within outward against a certain infinitesimal 

 surface {s), there is a resultant pressure p^; and that the opposed 

 pressure of the membrane before fertilization is just suflScient 

 to compensate this. Let the internal force F-^ = /?j s. Further- 

 more, it is conceivable, that, as a result of fertilization a chemical 

 splitting shall take place, by which p is increased; as a result of 

 this increase, something must change, perhaps the volume. It 

 might be supposed, then, that {s) would be thereby displaced, 

 for an infinitesimal distance, dl, giving, therefore, an infinitesimal 

 increase of volume, s d I = d v; the work, dfF, done by the system 

 in such a change, /. e., the changeinits volume energy is, therefore, 



dW = -dE= F,dl = psdl = pdv [ii] 



Now, any external force F^, directed against the internal force F-^ 

 and sufficient to prevent such a change, must be equal to F^; or, 

 since it acts on the same surface (s), and this is constant, the exter- 

 nal pressure equals the internal. 



Any finite change is, then, the integral of all the infinitesimal 

 changes, that is, 



pdv or - V d p [12] 



