ON THE OCCURRENCE OF MUCIN IN PLANTS. 



99 



but is not precipitated by adding water. As the precipitate 

 obtained by the addition of acetic acid to the extract of yam 

 root was insoluble in dilute hydrochloric acid and with difficulty 

 soluble in very dilute alkali (as i% solution of caustic soda), I 

 worked chiefly according to the method of Obolenski. 



The roots were cut into small slices, well crushed and 

 extracted with about three times the volume of water under 

 frequent stirring; the thick liquid thus obtained was filtered, 

 and the filtrate precipitated with a very dilute solution of acetic 

 acid gradually added. The addition of a large amount of acetic 

 acid at once, has to be avoided, otherwise the liquid will become 

 so thick, as to make filtering impossible. The precipitate was 

 washed with dilute acetic acid, and then with dilute hydrochloric 

 acid for the purpose of washing away a trace of another proteid 

 soluble in the latter acid; the precipitate was finally washed 

 with water, with alcohol and ether, and at last again with 

 absolute alcohol. Upon drying, the purified substance formed 

 a hard yellowish mass. 



3- Reactions and Composition- 



The substance obtained has the following chief reactions: 

 It dissolves in caustic alkali of about 2%, but with difficulty, 



and is soluble in strong mineral acids as well as strong acetic 



acid. 



It is not digested by artificial gastric juice, but easily by an 

 alkaline solution of trypsin. 



When concentrated sulphuric acid is added to its solution 

 in acetic acid, it yields a fine violet coloration. 



It gives the xanthoproteic and biuret reactions. 



By boiling with Millon's reagent, it forms a red precipitate. 



Tannin precipitates its solution. 



Double iodide of potassium and mercury yields a turbidity. 



By boiling for some time with 5% sulphuric acid, it yields 

 not only peptone, but also a substance which reduces Fehling 

 solution. 



The elementary analysis was made with the purified sub- 

 stance, dried at no°C. to constant weight, and yielded as 

 average of three experiments the following numbers: — 



