1920] 



MacDOUGA l—biocolloids 



*35 



give illustration of the special character or dissimilarity of consti- 

 tution of these mucilages when used to replace part of the agar. 

 First it is to be seen that in the biocolloids in which acacia, cherry, 

 and mesquite gum replace one another, the reactions to high H ion 

 concentration in the acid and to potassium hydroxide are not 

 widely different in total amount. The coefficient of increase in 





TABLE I 



Relative swelling of biocolloids in acids, hydroxides, salts, and water at 

 15 IN 0.01N concentration; increase in water given in percentages 



of original dried thickness or volume 



Material 



Agar 



Gelatine 



Agar ; 



Soy bean albumin . . . . 



Agar 



Opuntia mucilage 



Soy bean albumin 



Agar 



Cherry gum 



Soy bean albumin 



Agar 



Acacia 



Soy bean albumin . . . . 



Agar. 



Acacia 



Gelatine 



1 



Agar. . . . 

 Acacia . . 



Soy bean albumin 

 Gelatine 



Parts 



P 



H 



IO 



IO 



81 

 2/ 



KOH 



11.99 



33 



200 



50 



19 



29 



33 



no 



75 



NH4OH 



10.61 



83 



197 



45 



25 



41 



36 



91 



90 



KNO, 



6.6 



39 



80 



45 



47 



58 



67 



96 



67 



HNOj 



2.01 



44 



245 



32 



22 



26 



31 



48 



So 



HC1 



2.01 



44 



300 



23 



22 



28 



29 



48 



56 



Water 



(1800) 

 (I570) 



(2000) 



(2785) 



(2415) 



(2100) 



(1100) 



(1200) 



potassium nitrate does vary widely, however. The special effects 

 in ammonium hydroxide are discussed elsewhere. 7 



When these mixtures are viewed as homologues of cell masses 



or of plant protoplasm, that containing the Opuntia mucilage 



» MacDougal, D. TV, and Spoehr, H. A., The effect of organic acids and their 

 amino compounds on the hydration of agar and on a biocolloid. Proc. Soc. Exper. 

 Biol, and Med. 16:33. 1919. 



