170 MacDOUGAL and SPOEHR— plant PROTOPLASM. 



The superposed effects of alternated solutions may also be taken 

 to rest partly upon the complex structure of pentosan-protein com- 

 pounds. The replacement of one swelling reagent by another of 

 higher effect on agar does not have the effect of inducing a total 

 hydration of agar in excess of that which might be induced by the 

 second solution applied at the beginning. On the other hand the 

 replacement of a solution which might produce a maximum hydra- 

 tion by another which has a lesser effect does not usually result in 

 reducing the water content of the colloidal mass to the amount which 

 it would have taken up if swelled in this reagent from the beginning. 



The mixture of agar and gelatine however results in a condition 

 or structure in the colloidal mass in which it is possible to produce 

 or secure superposed effects. So far the only available example of 

 this action was a case in which an agar-gel mixture was first hy- 

 drated to full capacity in histidine dihydrochloride, making an in- 

 crease of 920 per cent. ; the amino salt was now replaced with potas- 

 sium hydroxide, making a total swelling of 2,950-3,447 per cent, as 

 compared with 2,556-3,090 per cent, which takes place in the 

 hydroxide alone. 



If the mass be supposed to be made up of alternating strands or 

 globules of the carbohydrate and albuminous elements, it is clear 

 that the action of the salt to which the sections were first exposed 

 would result in a much greater hydration of the gelatine than of the 

 agar. Replacement with the hydroxide would not result in the re- 

 duction of 'the salt induced swelling but would increase it at the same 

 time facilitating hydration of the agar. 



6 MacDougal, D. T., " Hydration and Growth," Publ. No. 297 Carnegie 

 Inst, of Wash., 1920, see pp. 17-20. 



