42 



Hydration and Growth. 



Table 25. 



sulphates. The differences found in my own tests with the above 

 mixtures, which, it must be pointed out, are so small as to be very close 

 to the limit of variation, are of the reverse kind. They are, however, 

 of such a nature as to warrant the assertion that the greatest swelling 

 of this biocoUoid in the group of substances 

 named does not take place in the nitrates 

 and chlorides. 



Another aspect of this matter was tested 

 by arranging a series in which an agar- 

 peptone mixture was swelled in two, con- 

 centrations of sodium acetate, which is re- 

 puted to retard imbibition in simple col- 

 loids, and sodium chloride, which is said 

 to increase the amount of swelling over 

 that of water. The measurements of such 

 swellings at 15° C, closed at the end of 24 hours, are given in table 26. 



These results are featureless, so far as the above point is concerned. 



The lesser concentration of the sodium acetate seems to give a 



greater swelling than the higher, but, on the other hand, the sodium 



chloride, which should promote imbibition, does not induce swelling 



as great as those in the acetate. The sections used were salt-free and 



a parallel series was run, using dried sections taken from the median 



layer of Opuntia joints, which at 15° C. gave the measurements shown 



in table 27. 



Table 26. Table 27. 



'Estimated from 0.007 M. 



The swelling in both salts is greater at the higher concentration, and 

 the maximum effect may Ue at a higher point. The acetate induces a 

 higher hydration effect than the chloride. The plant sections are of 

 course extremely complex as to chemical composition, although their 

 relations to water are taken to be chiefly determined by the pentosan- 

 protein ratio, and are modified by the salts already present and by the 

 residual acidity. It is evident that gelatine and isinglass do not 

 furnish conditions for swelling analogous to those of the plant, as as- 

 sumed by so many writers, since the results given above do not coincide 

 in the main with those obtained by Hofmeister.^ As has been pointed 

 out elsewhere in this work, the similarity of action of the plant to that 



1 Hofmeister, F. Die Betheiligung geloster Stoffe an Quellungs-vorgange. 

 Pathol, u. Phaim., 27:395, 1890, and 28:210, 238, 1891. 



Arohiv. f. Exper. 



