400 GRACE MEDES 



be due to the formation of H2CO3 from the COo of the air, since 

 H2CO3 + 2K0H ^ K2CO3 + 2H2O. 



Herbst considers hydroxyl also an indispensable constituent 

 of the medium for sea-urchin development and it is significant 

 that the processes which he finds especially affected are those 

 occurring early in development, — for example, fertilization and 

 the formation of the fertilization membrane. In his artificial 

 medium the optimum concentration varied in the different 

 forms employed. For Echinus it lay deeper than for Spaer- 

 echinus and the spermatozoa could endure a lower percentage 

 than the ova. Cleavage was accelerated up to a certain degree 

 of alkalinity; size and symmetry of the larva were also affected, 

 and were decreased both above and below a certain degree of the 

 hydroxyl. 



Herbst undertook to determine whether acids were evolved 

 by the embryos in the process of development and found by the 

 employment of various indicators that no strong acid was given 

 off. He performed a series of experiments in aerating his OH-free 

 water with 



a), air containing CO2, 

 b), CO2 free air, 

 c), CO2 and NH3 free air, 

 and concluded that the beneficial effect of the hydroxyl ions 

 is to neutralize the carbonic acid which is present in the water 

 in greater or less amounts, and which may be increased through 

 the metabolism of the animals. 



In the experiments recorded in this paper, however, the solu- 

 tions in which the eggs were developing were changed so often 

 during the first few hours after fertilization, that no oppor- 

 tunity was given for a decided accumulation of the products of 

 metabolism. Hence the neutralization of acids could not be 

 urged as an explanation of the fact that addition of NaOH caused 

 increase of rate of development. Even did this occur, still higher 

 concentration of hydroxyl would not produce increasingly 

 greater acceleration. 



The experiments of this series indicate, then, that: — 



a) Addition of acids produces an inhibitory effect upon 

 growth. 



