PROTOPLASMIC STRUCTURE 



95 



At present, however, our knowledge is insufficient for 

 any final estimate of its physiological importance. 



Since the effect depends upon the potential difference 

 between the walls of the pores and the mobile fluid layer 

 adjoining, all conditions that influence this potential 

 difference affect the character of the movement. The 

 rate of the movement or its direction or both may be 

 thus affected. The effects of salts, acids, and alkalies 

 are well illustrated in Perrin's investigations published 

 in 1904.^ The following table gives the results of a 

 typical experiment. The diaphragm consisted of naph- 

 thalene, and varying solutions of HCl and KOH were 

 used: 



This experiment and others of a similar kind show that 

 when a current of given intensity is passed through a 

 partition, the rate and direction of transport are deter- 

 mined by the charge of the partition substance, and 

 that this varies in a definite manner with the nature 

 and concentration of the ions present. 



Perrin also showed that the isoelectric point varied 

 with the nature of the diaphragm; thus partitions of 

 iodoform and glass were persistently negative, while 

 those of BaC03 and CrCl3 were positive. The electro- 



^ Perrin, /. Ckim. Pkys., II (1904), 601. 



