216 



HERBS 



Constituents. Bladderwrack yields to alkaline solutions a gelatine- 

 like substance found in other seaweeds and termed algin. The plant 

 yields by hydrolysis mannitol, fucose and arabinose. 



It also contains mannite and a small proportion of iodine. The 



latter appears to exist in the form 

 of an organic compound (Eschle, 

 1897), similar in its nature to the 

 iodine compound found in thyroid 

 glands. This is probably the most 

 important medicinal constituent of 

 the drug. 



The dry plant yields about 0-0113 

 per cent, of iodine (v. Itallie, 1889), 

 and 1-6 to 3-0 per cent, of ash, in 

 which chlorides and bromides are 

 present in addition to iodides. 



Algin is prepared commercially by 

 macerating seaweed in water and boiling 

 the insoluble residue in a solution of 

 sodium carbonate ; the algin (or alginic 

 acid) dissolves and is precipitated from 

 the filtered solution by " hydrochloric 

 acid ; the precipitate is redissolved in 

 soda and the solution evaporated on 

 glass plates ; it is used as a calico 

 dressing and for thickening the colours 

 used in calico printing. 



Use. Preparations of bladder- 

 wrack have been used medicinally 

 to reduce obesity. 



Varieties, &c. Fucus serratus, 

 Linne, also a common seaweed 

 occurring with F. vesiculosus on the 

 FIG. 113. Bladderwrack. Branch rocky shores of Great Britain, has 

 with reproductive organs, a serrated margin and no air- 

 Natural size. (Maisch.) vesicles, whilst F. nodosus, Linne, 



has the vesicles usually single, not 



in pairs. The constituents of these seaweeds are probably similar 

 to those of F. vesiculosus. 



AGAR-AGAR 



(Japanese Isinglass) 



Source, &C. The name agar-agar is now usually applied to a 

 gelatinous substance prepared in Japan from various species of Gelidium 



