THE PRODUCTS OF METABOLISM 



97 



The ratio of D- to L-galactose residues has been variously- 

 reported as 9 : i^^^ and 15 : 2^^^ and the exact constitution 

 of the polysaccharide is not yet agreed upon.^^^ 



Chondrus crispus, carragheen, which is now used as a 

 source of agar,^^^ yields two principal colloidal substances, 

 one more soluble in cold water than the other and giving a 

 viscous solution, and another forming a gel more readily.^^^ 

 The difference in physical properties between these two 

 appears to be due to the former being a mixture of sodium 

 and potassium salts, whereas the latter is chiefly a calcium 

 salt, the polysaccharide concerned, carragheenin, being 

 evidently the same in both.*^ The principal constituents 

 of carragheenin are D-galactose residues linked through 

 Cj and Cg and each having a sulphate residue on C4. Car- 

 ragheenin also contains L-galactose and other residues. ^^^ 

 Gigartina stellata ^^ and Iridaea laminarioides^^'^ evidently 

 contain polysaccharides of a similar nature. 



Fucoidin^^'''' ^'^^ is a mucilaginous material extractable 



-O3S.O 



-O3S.O 



H 



OH 



H 



H L/CH5 \ 

 H |S^ WO/ 

 J{ O O ^j ^H 



-038.0 



OH H 



-O3S.O 



-O3S.O 



