448 PROTOPLASM 



lyotropic series are reversed when the charge of the protein 

 changes from positive to negative. 



Lyotropic series of ions occur not only in regard to the effects 

 of ions on colloidal solutions but also in regard to the hydration 

 of other ions. Ions carry water molecules along with them; 

 this is an important factor in determining their migration rates. 

 They become grouped into a typical lyotropic series when 

 arranged in order of their hydration effects on other ions. 

 Such a series expresses the order in which the ions take up 

 water or affect the dissociation of water. Kruyt emphasizes the 

 fact that hydrogen ions cannot possibly be the sole cause of 

 lyotropic series. 



While a lyotropic, or Hofmeister, series is typical of protein 

 systems, valence may be equally evident. This is true of proto- 

 plasm; thus, work by Plowe on the extensibility of protoplasm 

 shows that while ions are grouped according to valence, there is a 

 pronounced difference among the individuals of a group ; and that 

 while the hydrogen ion (acidity) is a factor, it is not the only 

 factor. Protoplasm was stretched by microneedles and the 

 length of the thread measured. The following grouping of ions 

 resulted : 



Ca > Sr > Mg > K > Li > Na 



which means that protoplasm is poorly elastic in sodium salts 

 and highly so in calcium salts. While all the divalent ions are 

 together, calcium increases the elastic qualities of protoplasm to 

 a great degree, while magnesium has no noticeable effect what- 

 ever. The behavior of protoplasm when in an aluminum salt 

 (not included in the series) illustrates the relative effect of a 

 metal as such and of the change in acidity that it occasions. 

 Aluminum is known to increase the acidity of solutions. One 

 must, therefore, ascertain how much of the effect caused by an 

 aluminum salt is due to the aluminum ion itself and how much to 

 the increased acidity. In order to do this in the preceding experi- 

 ment, a solution of hydrochloric acid of the same pH value as the 

 aluminum solution was added to the cells. In this way, it was 

 ascertained that four-ninths of the increase in stretching capacity 

 of the protoplasm produced by an aluminum salt is due to the 

 aluminum ion itself and five-ninths to the increase in acidity. 

 Thus it is shown that part of an apparent ion effect may be due 



