Page:Popular Science Monthly Volume 32.djvu/560

542 the decay of muscular fiber in living animals; but yet, about sixty years after this event, we do not understand the chemical changes leading to that result. In a thousand other questions concerning the chemistry of human, animal, and vegetable organisms, our researches for finding satisfying interpretations have been futile, and even the most important query concerning the origin of life is likely to remain unanswered for many years to come.

There is a certain class of organic nitrogenous compounds, the origin, chemical nature, and decompositions of which are particularly far from being cleared up, although they concern the most indispensable functions of our own life, and are essential to vital energy in animals. Misunderstood, as many of their properties are, the facts which we know about them suffice to justify the high interest in their study which is manifested by chemists and physicians, as well as by the educated public in general. They are comprised under the name of albuminous matter, and have a very complex constitution, containing carbon, oxygen, hydrogen, nitrogen, and a small amount of sulphur. One of the chief features of their chemical character is a remarkable liability to decompose into the most various products. The best-known representatives of the group are—

1. Albumen, chief constituent of the white of egg and of blood-serum, dissolvable in water of common temperature, the dissolved matter coagulating and becoming insoluble when heated to 70° C. 2. Casein, dissolved as cheese in milk, coagulating upon addition of acids or certain ferments and warming. 3. Fibrin, coagulating from blood upon its exposition to air.

Plants are the manufacturers of albuminoids, or proteids, as they are also called; transformation of carbonic acid, water, and nitrogen, which are permanent constituents of the atmosphere and soil, into those combinations which constitute the body of plants, and which are designed to effect their propagation, is the chief function of the roots of plants. Among these combinations albuminoids are the most important, both for the vital process of the plants and as food for animals. From this reason the question of their origin has induced numerous investigations, to which we owe the knowledge that certain other nitrogenous bodies, called amides, which in varying amounts seem to be present in the roots of all plants at the time of beginning growth, play a prominent part in the genesis of albuminoids. The amides best known are asparagin (originally found in the shoots of asparagus) and leucin. The conclusion to which these researches have led is that sugar is formed in the root partly from starch by the action of diastatic ferment, partly by direct assimilation out of carbonic acid and water. Combination of sugar with one of those amides results. in the formation of vegetable albumen, from which the rest of the proteids are derived by slight variations of chemical composition. Vegetable albumen being of a very unstable nature, is partly again decomposed