82 



Hydration and Growth. 



water. Such progress is probably accompanied by, or consequent 

 upon, changes in the proteins and in the pentosans. On the other 

 hand, as the sections come nearer to their total imbibitional or 

 hydration capacity, they are more sensitive to acidity and not only 

 the speed but the amount of retraction increases. 



Another series was based on the behavior of an agar (90 parts) bean 

 albumen (10 parts) mixture in plates 0.18 mm. in thickness. Three 

 sets of sections were given treatment as nearly identical as possible, 

 a special feature being made of the action of salts. 



An initial swelling of 1,055 to 1,222 per cent, averaging 1,137 per 

 cent, was first produced in 7 hours in distilled water, at which time 

 it is evident the plates had increased to a thickness of about 2 mm., or 

 one-half of the total displayed in the test. (See fig. 13.) The replace- 



l?p.m. 



12 p.m. 



IZp.m 



12 p.m. m iZp.m 



I2p.m 



FiQ. 13. — Variations in thickness in sections of agar and bean albumen subjected to the action 



of acids, salts, and hydroxid. 



ment of the water by a hundredth-molar solution of potassium nitrate 

 (A) for 14 hours was characterized by a slight initial shrinkage, followed 

 by very slow swelling, which was probably accompanied by a solution 

 of the albumin from the sections. Replacement of the salt solution 

 by another one acidified by a hundredth-normal citric-acid solution (B), 

 produced a shrinkage which brought the dimensions of the sections 

 to about that at the end of the initial swelling in water. The material 

 might now be considered as a biocoUoid containing some salt and 

 acidified to a point probably equivalent to conditions in living material. 

 Replacement of the acidified salt with alkaline salt of the same con- 

 centration resulted in a swelling averaging 200 per cent of the original 

 thickness of the dried plate. 



The sections were now washed (D) and allowed to swell for 9 hours in 

 distilled water, making an increase of over 1,100 per cent and, as will 

 be obvious, bringing the water-content of the biocolloid to a point 

 nearing the maximum capacity. 



Replacement of water by an alkaline salt solution (E) now pro- 

 duced a greater shrinkage than when the biocolloid had a water-con- 

 tent about a half less, the loss being 200 per cent of the original thick- 



