VEGETABLE AND ANIMAL ALBUMEN. 543 



into amides and sugar, and, while the latter is used in accomplishing 

 the structure of the plant by changing into cellulose, the amide is 

 again transformed into albuminoid, and by decomposition reduced to 

 amides. Thus, by continually assimilating carbonic acid and water, 

 combining with them to form albuminoids, and giving them off again 

 as sugar, the amides act a prominent part in the develoi^ment of plants. 

 New supplies of amides, in the mean time, are continually formed, 

 while the albuminous matter is partly transferred to remote organs, 

 where, exposed to light and other agents, it undergoes various decom- 

 positions, by which the deposits of solid proteids, alkaloids, and many 

 other bodies are produced. A certain quantity of proteids becomes 

 stored up in the seeds, modified into gluten, or legumin, for the pur- 

 pose of hereafter entertaining and supporting the life and growth of 

 the offspring. Vegetable albumen, gluten, and legumin so closely re- 

 semble animal albumen, fibrin, and casein, that the same names have 

 been given to them. 



In thus tracing the origin of albuminoids in plants, we see them 

 partly dissolved as vegetable albumen in the juice (upon the heating of 

 which coagulated albumen gathers as foam on the surfa.ce), partly as 

 "plasma" forming the contents of cells, and partly as solids in various 

 organs, but chiefly in the seed, which by their presence acquires more 

 or less valuable properties as food for animals, the nutritive value of 

 grain and leguminous products being due merely to the high percent- 

 age of gluten and legumin contained in them. 



Plants, indeed, are the sole source on which most animals depend 

 for their food, for they are incapable of assimilating the constituents 

 of air and water, as vegetables do. Only in the most simple forms of 

 animals, such as moneres and amoebte, the question is undecided whether 

 such an assimilation takes place or not ; but our knowledge of the 

 limits between these low forms of vegetable and animal beings is very 

 imperfect, and, in view of the numerous parasitic plants which draw 

 their food from other organisms, we can not declare the source and 

 process of nourishment to be a correct and pervading mark of differ- 

 ence between the two classes. If, however, some one should raise the 

 objection that animals of prey do not depend upon plants for food, he 

 might easily be corrected by showing that, in feeding on vegetable- 

 eating creatures, they " indirectly " live on the plants themselves. 



The changes which vegetable prot-eids undergo by being taken up 

 into the animal organism are insignificant at first ; having been trans- 

 formed into soluble bodies (peptones) by pepsin, the digestive agent 

 of the stomach, we see them appearing again in the circulation of blood 

 as albumen, globulin, fibrinogen, combinations of very similar charac- 

 ter to the proteids of plants. There is, indeed, no practical difference 

 existing between albumens and legumins. The proteid of beans, peas, 

 lentils, etc., is identical with casein, the proteid of cheese, as to com- 

 position and properties. 



