136 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
Before going farther, we should point out that the minimal 
value of concentration for an acid to prove effective is not quite 
the same for eggs of different females. In my experiments upon 
the causation of development of sea-urchin eggs by means of 
the blood serum of warm-blooded animals, it has been an ever- 
recurring observation that these experiments only succeed for 
a part of the eggs of a female, unless the eggs are previously 
sensitized by a treatment with SrCl, (see chap. xviii). I 
regard the variation in permeability of the eggs of different 
females to acids or blood as responsible for these individual vari- 
ations. The mass of the eggs also exerts some influence. If 
too many eggs are placed in the solution, the stated mass of 
acid is not enough. 
Overton observes that the narcotic effect of the dihydric 
alcohols is much weaker than that of the monohydric alcohols. 
I find that the monobasic acids of the former series exhibit a 
much weaker effect with regard to membrane formation than the 
corresponding members of the series of acids of the monatomic 
alcohols. I may quote as evidence experiments with oxypro- 
pionic and oxybutyric acids. 
TABLE XXI 
Oxypropionic AcIp B-OxysButyric AcIp 
LENGTH OF ExposuRE 
N/500 4/500 N N/500 | 2/500 N 4/500 N 
fumintite de ct.cenrse 0 ) 0 5% 100% 
QaMInWbes serene: 0 2% 0 LOO. ct a ee 
3 minutess.ac0. 0 60 8% ~ =) See | eee 
AMMINUGES|:. «420-1 oes 0 90)" | Ss Se ee eee 
FSI GES el sienecaien: 0 
It will be seen from a comparison between this and the pre- 
ceding table that B-oxybutyric acid possesses only a quarter of 
the efficiency of butyric acid, and that propionic acid is more 
than four times as effective as lactic acid. The oxy-acids also 
