GLUTEN, VEGETABLE ALBUMEN, AND DIASTASE. 117 



through the sieve in preparing the gluten of wheat, the water rests trans- 

 parent and colourless above the white sediment. If this water be heated, 

 it will become more or less troubled, and white films or particles will 

 separate, which may be easily collected, and which possess all the pro- 

 perties of coagulated albumen, or boiled white of egg. To this sub- 

 stance the name o[ vegetable albumen has been given. When the fresh 

 prepared gluten of wheat is boiled in alcohol a portion of albumen gene- 

 rally remains undissolved, showing that water does not completely wash 

 it out from the gluten. 



Vegetable albumen, when fresh and moist, has neither colour, taste, 

 nor smell, is insoluble in water or alcohol, but dissolves in vinegar and 

 in caustic potash or soda. When dry it is brittle, more or less coloured, 

 and opacjue. In the seeds of plants, it exists only in small quantity — 

 thus the grain of 



Wheat contains | to 1^ per cent. 

 Rye ... 2 to 3| 

 Barley • • , • iV to i 

 Oats . . . ^ to i '♦ 

 It occurs more largely however in the fresh juices of plants, in those 

 of cabbage leaves, turnip roots, and many others. When these juices 

 are heated the albumen coagulates and is readily separated. 



Gluten and vegetable albumen appear to be as closely related as sugar 

 and starch are to each other. Like these two substances, they consist 

 of the same elements, united together in the same proportions, and are 

 capable of similar mutual transformations. According to the most re- 

 cent analyses, those of Dr. Scheerer, they consist of 

 Carbon ^ = 54-76 

 Hydrogefr = 7-06 

 Oxygen = 20-06 

 Nitrogen = 18-12 



100 



When exposed to the air in a moist state these subftances undergo de- 

 composition. They ferment, emit a most disagreeable odour, and pro- 

 duce, among other compounds, vinegar and ammonia. 



The important influence which gluten and vegetable albumen are 

 supposed to exercise over the nourishing properties of the different kinds 

 of food in which they occur, will be considered in a subsequent part of 

 these lectures.* 



3°. Diastase. — When cold water is poured upon barley newly malted 

 and crushed, is permitted to remain over it for a quarter of an hour, is 

 then poured off, filtered, evaporated to a small bulk over boiling water, 

 again filtered if necessary, and then mixed with much alcohol, a white 

 tasteless powder falls — to which the name of diastase has been given. 



* There occur in the animal kingdom— in the bodiesof animals— three other forms of the 

 substance above described under the names of gluten and vegetable albumen. These are 

 albumen or white of egg, already mentioned, — casein, the curd of cheese,— and fibrin^ the 

 substance of the muscular fibre of animals. 



1^. Casern.— When the curd of cheese is well washed with water, and then boiled la 

 alcohol to free it from oily matter, it foraxs the casein of chemists. While moist it is soft 

 and colourless, but as it dries it hardens, assumes a yellow colour, and becomes semitrans- 

 parent. Even when moist it is perfectly insoluble either in cold or in hot water. It is solu- 



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