150 



Papers from the Department of Marine Biology. 



surface tension of water. The relation was pointed out by Traube and 

 supports his theory that the more a substance lowers the surface tension 

 of water, the more readily it will pass into cells. Loeb had previously 

 pointed out that the more lipoid soluble acids were most efficient in 

 membrane formation, and suggested lipoid solubility as the determining 

 cause of efficiency. Both of these views assume, of course, that the 

 acids to produce their effect must enter the cells. The ability of acids 

 to change negatively heliotropic to positively heliotropic copepods 

 seems to depend likewise on either their surface tension or their lipoid 

 solubility. On the other hand there are certain effects of acids which 



TABLE 3. 



iConc. which just kills in 7-30 min.; after Barratt, Zeit. f. alleg. Physiol., 4, p. 441, 1904. 



'Cone, which just causes haemolysis. Fiihner u. Neubauer ,Arch. f. exp. Pathol., 56, p. 333, 1907. 



Cone, which just prevents growth. Kahlenberg and True, Bot. Gaz., 22, p. 81, 1896. 



Loeb, Bioc. Zeit., 23, p. 95, 1909. 



'Loeb, Pfluger's Archiv, 69, p. 1, 1897, and 71, p. 457, 1898. 



Loeb, Bioc. Zeit., 15, p. 255, 1909. and Loeb, Artificial Parthenogenesis and Fertilization, p. 143, 1913. 



seem to depend on the strength of the acid, for instance the haemolysis 

 of blood corpuscles, if we can judge from the few results of Fiihner and 

 Neubauer; also the absorption of water by muscle. In these pro- 

 cesses capillary activity and lipoid solubility play a subordinate role. 



Turning now to a comparison of the penetration rate into the tissues 

 of the "prickly fish" with the physical properties of the acids we find 

 again that there is no exact agreement in any case (table 2). Degree 

 of dissociation is certainly not the determining factor in penetration, as 

 a glance at the table will show. No one can deny but that there is a 

 certain correspondence between lipoid solubility and capillary activity 

 and penetration rate, yet it is far from exact. With acids as with so 

 many other classes of substances it is only true in general that those 



