542 THE POPULAR SCIENCE MONTHLY. 



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 indispensa- 

 ble functions of our own life, and are essential to vital energy in ani- 

 mals. Misunderstood, as many of their properties are, the facts which 

 we know about them sufiice 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 suljihur. 

 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 im- 

 portant, both for the vital process of the plants and as food for ani- 

 mals. 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 groAvth, 

 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 Avhich these researches have led is that 

 sugar is formed in the root partly from starch by the action of dias- 

 tatic 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 



