242 HEALTH AND DISEASE 



sented by the gluten of wheat, the legumin of beans and peas, and the 

 aleuron grains of many seeds. Chemical analysis shows that they contain, 

 in every 100 parts, 52 of carbon, 7 of hydrogen, 16 of nitrogen, and 24 of 

 oxygen, with about 1 per cent of sulphur. In the animal they exist in two 

 conditions — in the fluid and soluble, as in white of egg, the fibrin and 

 albumen of blood, and the casein of milk; and in the solid and insoluble 

 form, as in the substance of muscle, connective tissue, and the protoplasm 

 of various cells. 



The starches, sugars, and gum have been classed together under the 

 general term of the carbohydrates, since one of their constituents, carbon, 

 is combined with oxygen and hydrogen united in the proportion to form 

 water. The compositions of several varieties is represented by the formula 

 C 12 , H-°, O 10 , of others by C 12 , H 24 , O 12 . The starches are very widely dis- 

 tributed in plants, ajipearing as the first evident products of assimilation, 

 and being formed by the decomposition of the carbon-dioxide contained 

 in the air and water they absorb. They are sometimes found in solution, 

 as in the case of various sugars, but more commonly in the form of grains 

 occupying the spaces in the interior of cells, and constituting a reserve of 

 nutriment which is drawn upon in the course of the growth and develop- 

 ment of the plant, but which is also a valuable aliment capable of being 

 assimilated by animals. Starch is abundant in many fruits, as in the banana 

 and tig; in seeds, as in those of all the cereals; in rhizomes, as in the 

 arrow-root; in tubers, as in the potato; and in stems, as in that of the sago 

 palm. The process of the ripening of fruit consists in large measure in the 

 change of starch into pectin, dextrin, and sugar, under the influence of 

 light and heat. The particular form of sugar, as cane, grape, beet, maple, 

 eucalyptus, or mushroom, depends on the special activities of the plant, 

 and the several forms differ inter se in their solubility, crystalline form, 

 chemical composition, action on polarized light, and other characters. 



The oils found in plants are divisible into two groups, the fixed and 

 the volatile. The fixed oils are compounds formed of glycerine united with 

 the fatty acids; thus, palmitin is composed of glycerine and palmitic acid, 

 stearin of stearic acid and glycerine, olein of oleic acid and glycerine. The 

 process of emulsification is simply that of reducing them to fine globules 

 by shaking them up with any glairy fluid. Such emulsions may last 

 unchanged for a considerable period, but as a rule the mist of oil runs 

 together into droplets and these again into drops, which collect together, 

 and the original condition of a layer of oil is recovered. There is no 

 chemical alteration in emulsification. The process of saponification is, on 

 the contrary, attended with a profound change in the chemical composition 

 of the oil or fat. It is effected when the oily substance is intimately 



