Fundamental Features of Phytocolloids. 



19 



cut from the extreme margin of the plate would doubtless have shown 

 some elongation. 



The marginal strip of a plate consisting of 6 parts agar, 3 parts gum 

 arable, and 1 part gelatine which had a length of 15 cm. increased to 

 15.5 cm. in 45 hours. To be compared with this elongation of 3 per 

 cent is that of the increase of a pile of sections 2 cm. in height cut from 

 the same plate, which rose to 15 cm. in 24 hours, showing an increase 

 of 750 per cent. The proportion would doubtless have been still 

 greater had the swelling of one section been measured alone, as trios 

 of sections cut from the middle of the plate showed swellings of 1,141 

 per cent at 14° to 17° C. 



Fig. 6. — Demonstration of the swelling of sections of plates of agar 4 parts, opuntia mucilage 

 4 parts, gelatin 1 part, bean protein 1 part, in thickness with but little increase in length, due 

 to the manner in which the moist colloid was held while drying. 



Another test of the same kind is illustrated by figure 6. Sections of 

 a plate consisting of 4 parts agar, 4 parts opuntia mucilage, 1 part gela- 

 tine, and 1 part bean protein were placed in a frame of glass rods and 

 immersed in a vessel of distilled water, swelling from a total thickness 

 of 15 mm. to a total of 180 mm., while a strip cut from this plate which 

 had an initial length of 8 cm. had elongated to 8.5 cm. The increase 

 in thickness was 1,200 per cent, while that in length was but 6 per cent. 



Plates of gelatine invariably showed a greater increase in areal 

 dimensions than that of biocolloids such as those mentioned above, and 



