34 



Scientific Proceedings (102). 



the protoplast, and presumably intimately interwoven into its 

 colloidal mesh. In animals the pentosans seem to be confined 

 to the nucleo-proteins, and the manner of their origin is not so 

 clear in this case. 



C. The mucilages, gums and slimes in which form these sub- 

 stances appear in definite masses in syneretic cavities and in 

 layers in the plant cell have a hydration capacity enormously 

 greater than that of the sugars from which they are derived, and 

 show a wide range of solubility and other qualities. 



D. The pentosans are subject to digestion in animals to an 

 extent variously assigned by different authors. These sub- 

 stances undergo metabolic changes in the plant but slowly. 

 Wherever they occur they must show changes in volume and form 

 according to the colloidal structure in which they occur and to 

 the nature of the solutions penetrating them. 



Our own experimentation has been made principally with agar 

 and some of the common plant gums, separately and in mixtures 

 with albumins. The revised generalizations which we are pre- 

 pared to support may be briefly stated in the following summary: 



1. The pentosans are weak acids which dissociate so slightly 

 that 1 per cent, solutions of agar, acacia and cherry gum showed 

 pH values of 5.1 as determined by the indicator method. The 

 mucilage of Opuntia showed a value of 5.8. The swelling of 

 these substances in the amino-acids which dissociate strongly, as 

 aspartic acid which shows a pH of 3 at 0.0 1 M is less than in water. 



2. Such acids and other amino compounds as asparagin, 

 pH = 6.2, alanin pH = 7.0, phenyl-alanin pH = 4.8, glycocoll 

 pH = 6.2 at 0.01 M as tested by the indicator method, ammonium 

 hydroxide and ethylamine facilitated the hydration of agar so 

 that it showed swellings greater than in distilled water. 



3. Other factors than the hydrogen ion concentration are 

 determinative in this action as illustrated by the fact that swellings 

 in phenyl-alanin and glycocoll are fairly equal. The total swelling 

 of agar as compared with that in water as unity was 1.26 in aspar- 

 agin, 1.52 in alanine, 1.65 in glycocoll and in phenyl-alanin, in 

 ammonium hydroxide and in ethylamine, all in 0.01 M solutions. 

 Propionamide the only amide tested did not exert any marked 

 effect on swelling except to retard it slightly at 0.01 M and in 

 stronger solutions. 



