THE GENERAL NATURE OF A FOOD 



135 



FIG. 72 



combine it with nitrogen-bearing radicles of the soil to form proteids. 

 It is then the chlorophyll, very like hemoglobin, which synthesizes certain 

 inorganic elements into more complex substances, protein, fats, and 

 carbohydrates. These three with water and inorganic salts make up the 

 necessary food of all animals. These proteids, fats, and carbohydrates, 

 stored with the potential energy coming from the sun, expended in mak- 

 ing them, animals again analyze into simpler compounds, and these are 

 essentially those with which the plants again begin their work. The 

 stored energy thus liberated is the originator of the movements which 

 life, especially animal life, essentially is. The formula 



(6CO 2 + 5H 2 O) n = (C 6 H 10 O 5 ) + O n 



is, therefore, typical for the synthesizing function of plants, and its 

 reversal 



(C 6 H 10 5 ) n + O = (6C0 2 + 5H 2 0) n 



is characteristic of the analyzing, energy-liberating function of animals. 

 Plants and animals in this way are mutually dependent, and thus runs 

 the eternal round of matter. It is the es- 

 sence of vegetable life, so far as we are at 

 present concerned with it, to synthesize 

 the molecule of starch, but it does this 

 only through the obscure agency of the 

 chlorophyll of its verdure. This sub- 

 stance, it is interesting to note, is largely 

 a proteid, the baffling nature of whose 

 life-mystery has already been pointed out. 

 Nutrient Proximate Principles. The 

 table of chemical compounds (page 30), 

 already isolated from a highly evolved 

 animal body, is made up chiefly of six 

 classes of substances: protein, fats, carbo- 

 hydrates, albuminoids, inorganic salts, 

 and water. Each one of these classes is 

 probably represented, at least in minute 

 amount, in any particle of living matter, 

 for analysis of masses of the purest proto- 

 plasm obtainable always shows the pres- 

 ence of at least the first three of these 

 and water. Logically, then, these deter- 

 mine what foods animals require as sup- 

 plyers of tissue, and we find, in fact, that 

 all actual nutrients used by man the world over may be divided into the 

 six classes proteids, albuminoids, fats, carbohydrates, inorganic salts, 

 and water. If we are guided by empirical conditions of actual diets, 

 we must add to these two other classes, stimulants and condiments, the 

 latter of essential importance. 



A fibula tied in a knot, after mac- 

 eration in acid to remove its lime, etc. 

 (From a specimen in the College of 

 Physicians and Surgeons, New York.) 

 (Dalton.) 



