132 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
It can be seen from this that solutions of various substances 
which are all theoretically isosmotic do not on that account 
possess the same degree of physiological activity. It is there- 
fore necessary to differentiate between theoretically isosmotic 
and physiologically isotonic solutions. The two values are 
more nearly identical for the red blood corpuscles than for the 
sea-urchin egg. This will be made clear by the following table 
in which is set forth the optimum concentration of solutions of 
various substances with regard to artificial parthenogenesis. For 
this optimum concentration can be very sharply determined by 
choosing a definite length of exposure, such as 55 minutes at 
about 15° C. 
TABLE XVII 
OptTiImMuM CONCENTRATION OF SOLUTIONS OF VARIOUS SUBSTANCES FOR 
ARTIFICIAL PARTHENOGENESIS 
Optimum Con- Osmotic Pressure 
contrationn Dissociation of 
Constitution of the 
Solution Grammolecules the Solution ie Atobepbeese es 
Caneisicamasecm erie 0.96 oS Dil e 
Grape sugar secs <scss 1.04 a 23.33 
Ca@ ern wc cutee 0.50 64 25.57 
Mig © varstencsenecopetaciehes 0.49 70 26.47 
1 Gr( ©) be ee ee epoca 0.74 66 27.59 
ING Wlitcsk sce creets 0.79 71 30.28 
KCl. 0.78 Uf 30.95 
Of course these values which were obtained with S. purpur- 
atus at Pacific Grove do not apply as they stand to any given 
form of sea-urchin in any given locality. We have no explana- 
tion to offer for these discrepancies except in the case of sugars 
where the discrepancy seems to find its explanation in the 
abnormal physical behavior of concentrated solutions. It is 
possible that these salts modify the permeability of the egg in 
a different degree or sense and that this accounts for the dis- 
crepancies between calculated and observed results. 
