354 MacDOUGAL— HYDRATION AND GROWTH. 



form sections 0.13 mm. thick on filter paper. Swellings at 15° C. 

 were obtained as follows : 



Distilled Water. Glycocoll. 



.03 Hi. 0.05 M. o.oi M. 



1380% 1382% 1077% 1462% 



This gum liquefies irregularly and hence the figures show the 

 extent of swelling before active dispersion of the mass begins. 



Next a mixture of 9 parts of gelatine and i part tragacanth was 

 made up at 2.5 per cent, to correspond to a similar mixture of gela- 

 tine and Opuntia mucilage. Swellings as follows at 15° C. were 

 obtained : 



Distilled Water. Glycocoll 



0.3 HI. 0.05 M. 0.01 M. 



1320% 1520% 1040% 1320% 



Nothing may be concluded on the basis of these figures except 

 that the hydration of this material reaches a stage where it goes into 

 dispersion unevenly and in a manner which makes auxographic 

 readings, as well as all mass or weight determinations, of doubtful 

 value. 



The above tests were repeated with Opuntia mucilage with the 

 following results : 



Distilled Water. Glycocoll (15° C). 



0.3 M. 0.05 M. o.oi M. 



923% 800% 654% 600% 



It is highly probable that the high relative swelling in the more 

 concentrated solution is due to the hydrogen ion effects on the gela- 

 tine as glycocoll is known to show some dissociation in this way. 



Sections consisting of 4 parts agar and i of gelatine which had 

 an average thickness of .3 mm. swelled as follows at 15° C. in gly- 

 cocoll. 



0.3 M. .05 i1/. .01 J/. .002 M. 



1550% 1233% 1960% 1767% 



The average swelling of such sections in water was about 1700 

 per cent., and the irregularity characteristic of auxographic measure- 

 ments of the action of this amino-acid is seen in the above results. 



