AGRICULTURAL CHEMISTRY. 125 



Albuminoids or Nitrogenous Vegetal Principles. 



Carbon. Hydrogen. Oxygen. Nitrogen. Sulpliu. 



Vegetal albumin 54.8 7.3 21.1 15.9 0.9 



Vegetal fibrin, or gluten ■• • 54.0 7.2 22.3 15.7 0.7 

 Vegetal casein 54.6 7.4 21.7 15.8 0.5 



These bodies differ considerably in certain characters, though 

 their similarity in others is very strongly marked. In composition 

 they are almost identical. From the difficulty of obtaining them in 

 the pure state their precise composition is not definitely known. The 

 figures in the table represent the mean results of the best analyses. 



The names albumin and casein originated from animal substances, 

 and in fact we find in the animal kingdom a series of bodies corres- 

 ponding almost perfectly with the vegetable nitrogenous principles. 



In the white of the egg, in the serum of blood, and in many diseased 

 animal secretions, we meet with albumin which has the property of 

 passing from its usual fluid condition into the solid form on the appli- 

 cation of heat. It is said to coagulate. 



In the vegetable, albumin exists in much smaller relative quantity 

 than in the animal; but it may be found in the juice of nearly all 

 plants. If potatoes, turnips, or flour be digested for some time in 

 water and the liquid then allowed to clear by settling, it contains a 

 minute quantity of albumin in solution, as may be made evident by 

 heating it, when a coagulum of this body separates. 



Casein is an ingredient of the milk of animals. Heat does not 

 coagulate it, but acids have this effect. Cheese has casein for its 

 characteristic constituent. 



In the seeds of leguminous plants, as the pea and bean; in the pea- 

 nut and almond, this body exists very abundantly. 



If crushed peas are soaked some hours in warm water, to which a 

 little ammonia is added, they yield casein to the liquid, and on the 

 addition of an acid it is separated as a curdy matter like the casein 

 of milk. In China a kind of cheese is thus largely manufactured. In 

 smaller quantity casein is found in all the grains and seeds used as 

 food. 



Gluten exists in wheat, and may be obtained by slowly washing a 

 dough made from wheat flour, whereby the starch is removed and a 

 glutinous mass remains which is the substance in question. As thus 

 seen, it is mingled with more or less albumin and casein, as well as 

 oil and starch. Gluten is the characteristic ingredient of those grains 

 from the flour of which a light raised bread may be made. Liebig 

 has given to gluten the name vegetable fibrin, from its analogies with 

 the fibre of flesh or animal fibrin. 



The albuminoids, like the carbo-hydrates, are easily susceptible 

 of mutual* transformation. In the animal the casein of milk or beans, 

 the albumin of eggs or of vegetables, and gluten, are converted first 

 into albumin and liquid fibrin in the shape of blood, and afterward 

 into the solid flesh. So, too, in the plant, similar changes, without 

 doubt, occur. 



To some extent these conversions may take place outside the or- 

 ganism. If, for example, animal fibrin be exposed with water to the 



