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 1% 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:— 
