V^'>^ 



8io BIOPHYSICAL PHENOMENA [pt. iii 



against the osmotic pressure of the solution. The resulting graph 

 showed the usual descending curves, for the higher the osmotic 

 pressure the more quickly the abnormalities appeared, but in one case 

 a complete curve was drawn through only two points, and in two cases 

 through only one point — happily an unusual way of presenting facts. 



Spaulding's work on the energy of segmentation, though it was 

 earlier and based on excellent theoretical principles, was very similar 

 to that of Vies & Dragoiu. By immersing echinoderm eggs in solu- 

 tions of differing osmotic pressure, he was able to find the solution 

 which just stopped cleavage, thence the internal osmotic pressure, 

 and thence the energy in ergs required to stop cell-division. The 

 osmotic pressure sufficient to inhibit the first segmentation, and there- 

 fore equal to the resultant internal pressure, was 7-32 atmospheres, 

 for the second segmentation 6-53, and for the third 6-40. From this 

 he calculated that the energy required to stop the first division was 

 1-567 ergs, and that required to stop the second one was 1-399 ^^S^. 

 'This means", he said, "that, as involved in or as identical with the 

 first segmentation, there has been a resulting energy decrease, there- 

 fore, of 0-168 erg, or that it has taken this amount of energy, about 

 1/9 of the total increase resulting from fertilisation, etc., to bring 

 about this cleavage." Similarly, to bring about the second cleavage, 

 0-028 erg was involved. 



The conclusions of Spaulding and of Vies & Dragoiu were for a 

 time generally accepted, but the conception of "travail d'arret" has 

 now, largely owing to the criticisms of Rapkine, fallen into disrepute, 

 for it rests on a fallacy, assuming as it does that it would be possible to 

 find the work done by a man in walking a mile by measuring the work 

 done in stunning him with a stick or a stone at the end of it. " In order 

 to use the 'travail d'arret' as a measure "of the 'travail de division' 

 the phenomena would have to be reversible, i.e. capable of coming 

 to equilibrium, but that is just what they are not." (Rapkine.) 



Bialascewicz approached the problem in another way, estimating 

 the relative speed of development of embryos in solutions of different 

 osmotic pressures. Working with Echinus microtuberculatus , Strongylo- 

 centrotus lividus and Ranafusca, and using hypotonic and hypertonic 

 sea water in the two first cases, and glucose in the third, he found that 

 the maximum speed of development took place in a medium isotonic 

 with the normal medium, and on both sides of which the rapidity 

 of development fell off sharply. These bell-shaped curves are shown 



