Physiological Efficiency of Acids 



137 



show increasing effectiveness with the number of carbon atoms; 

 for /3-oxybutyric acid is about twice as active as oxypropionic 

 acid. A comparison of oxybenzoic with benzoic acid showed 

 that the latter is ten times as effective as the former. 



Perhaps, however, the influence of the constitution of the 

 acid is most clearly demonstrated by a comparison of the effect 

 of ;8-oxybutyric acid and oxyisobutyric acid, ^-oxybutyric 

 acid has more than four times the effect of oxyisobutyric acid. 

 This is probably coimected with the fact that while jS-oxybutyric 

 acid has the same carbon chain as butyric acid, oxyisobutyric 

 acid has a branched carbon chain. 



Experiments upon di- or polybasic acids prove a trial of 

 patience, as one cannot with certainty rely upon success. 

 Whereas propionic, butyric, and valerianic acids cause mem- 

 brane formation in all eggs of S. purpuratus practically without 

 exception (provided that the concentration of acid and length 

 of exposure are correctly chosen), the di- and polybasic organic 

 acids do 'not affect the eggs of all females. Hence these acids 

 behave like foreign blood sera, as regards membrane formation. 

 This analogy indicates that the dibasic acids have a weaker 

 effect than the monobasic acids, because they enter the egg 

 more slowly. For obviously the degree of permeability of the 

 egg differs in various females. In the next table I have put 

 together results obtained from the eggs of an especially "favor- 

 able" female with oxalic, succinic, tartaric, and citric acids. 



TABLE XXII 



Length of Exposure to — 



1 minute. 



2 minutes 



3 minutes 



4 minutes 



5 minutes 



6 minutes 



1 . 7/500 N 

 Oxalic Acid 







15% 

 20 

 90 

 90 



7/500 N 



Succinic 



Acid 





 

 

 



2% 



7/500 N 



Tartaric 



Acid 



10% 

 100 



4/500 N 

 Citric Acid 





 



10% 

 60 

 80 

 90 



