80

GLUTEN AND ALBUMEN.

similar; they exist in plants in smaller quantities thanthe three substances already described; but they arenevertheless most important, and of especial interest, astheir presence in vegetables is essential to their value asfood.

237. When the clear juice of any plant is boiled,there usually collects on the surface a thick green scum,which may easily be separated by straining the liquorthrough linen. This scum consists almost [entirely ofalbumen and gluten; they are associated together, andexist in greater or less quantity in almost all plants. Ingeneral the seeds of plants contain even a larger propor-tion of these substances, than the plants themselves.

238. The flour of wheat contains a considerable pro-portion of gluten; it may be readily separated from flourby tying a portion of thick paste in a piece of linen, andthen kneading the paste thus enclosed in linen under astream of cold water; by this process all the starch willgradually be washed out, and at last there will remainin the linen nothing but gluten.

239. Pure gluten, when thus obtained, is a greyishwhite, soft, solid substance, elastic and tough, andalmost resembling a piece of animal skin in appearance ;it may be dried by carefully warming it till all the waterwhich it contains is evaporated; and when dry may bepreserved for a long time without undergoing any change.

240. In its moist state, or as it is obtained, by washing a thick paste of flour in the manner above described,gluten is very liable to decompose. Both this substance