300 E. G. Spaidding 



furnished. Accordingly this event will have been brought under 

 the Four Laws of Energetics. 



THE EXPERIMENTAL METHODS 



The practical problem very evidently resolves itself into that of 

 finding an efficient means of compensating, of establishing these 

 equilibrium conditions. Since, now, by hypothesis, we are deal- 

 ing with resultant pressures, it is clear that there can be used as 

 a compensating means, only such an one as will give us a pressure 

 which will supplement that of the egg membrane and be opposed 

 in direction to the resultant pressure from within. 



This means is found in the pressure of substances in solution, 

 /. e., in osmotic pressure. The law for osmotic energy (solutions) 

 is, as is well known, m general the same as that for gases, namely, 

 pv =RT. 



It would appear, then, that, by using such an osmotic solution 

 as has a pressure just equal and yet opposed to that increment in 

 the outwardly-directed pressure which results from the fertiliza- 

 tion of the ovum, the egg could be kept from segmenting, and a 

 measure of this increment would be obtained. This can, in fact, 

 be done, but with it two precautionary measures must be taken. 

 For, first, since the normal medium of the eggs (arbacia) used is 

 sea-water, and since it is known that the absence of this or of cer- 

 tain ions which it contains prevents segmentation,^ it is necessary 

 to retain this "ionic environment" in the experiments. But with 

 this environment constant, since its efi^ect on normal segmentation 

 is also a constant one, this effect need not be taken into further 

 consideration in the results of our experiments. In the second 

 place, any inhibitory result coming from the chemical action of 

 the solution on the ova must be eliminated; that of which exclusive 

 use IS to be made, in both experimentation and computation, is 

 the "pressure effect" of the solution employed. 



Now these two necessarv conditions can be gained by the use of 

 a solution of cane sugar in sea-water. For, thereby, first, although 



'R. S. Lillie: Fusion of Blastomeres and Nuclear Division without Cell-division in Solutions of 

 Non-electrolytes. Biol. Bulletin, iv, 4, March, 1903. 



