A manual of practical hygiene, for students, physicians and health officers / by Charles Harrington.

  • Harrington, Charles, 1856-1908.
Date:
[1911], ©1911
Catalogue details

Licence: Public Domain Mark

Credit: A manual of practical hygiene, for students, physicians and health officers / by Charles Harrington. Source: Wellcome Collection.

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    (6) Peptones. Soluble in water, uncoagulated by heat, but not pre¬ cipitated by saturating their solutions with ammonium sulphate.1 (c) Peptides. Definitely characterized combinations of two or more amino-acids, the carboxyl group of one being united with the amino group of the other with the elimination of a molecule of water.2 The albumins are not precipitated by alkaline carbonates, common salt, or dilute acids, but they are coagulated by being heated to 65°— 73° C. Casein, legumin, conglutin, syntonin, and albuminates, on the contrary, are not coagulable by heat, but are precipitated by common salt, sodium acetate, and trisodium phosphate. The albumoses are widely distributed throughout the vegetable kingdom, and are found largely in the cereals. In the animal kingdom, they are intermediate products of the action of pepsin on ordinary proteids, becoming even¬ tually converted to peptones. The collagens are very rich in nitrogen, but have an inferior nutritive value. Gelatin, for instance, contains 17—18 per cent., while the albumins contain but 16. Fats.—The fats are compounds of the triatomic alcohol, glycerin, with fatty acids, mainly stearic, palmitic, and oleic. These several compounds are known as stearin, palmitin, and olein. The two first mentioned are solids at usual temperatures, while olein is a liquid. Most fats are combinations of two or all of these substances, and some, as, for example, butter, contain additional glycerides in small amount. Stearin and palmitin being solids, and olein liquid, the consistency of a fat is dependent upon the proportions in which these substances are present. Stearin is a component of most animal fats, but never is found in vegetable fats. The chief constituent of animal fats is pal¬ mitin, and this occurs also in nearly all vegetable fats. Olein exists in both. Butyrin, caprin, caproin, and caprylin are glycerides of volatile fatty acids present in the fat of milk. Fats consist of carbon, hydrogen, and oxygen, and contain no nitro¬ gen. The hydrogen and oxygen are not present in the proportions in which they exist in water and in carbohydrates, the oxygen being de¬ ficient. As taken in food, fats are chiefly in the form of neutral substances, but more or less free fatty acid is always present, and in some foods which have been kept for a time, particularly in well-ripened cheese, fatty acids may be present in a free state in quite large proportion. The. fats play an important part in the maintenance of animal heat and mechanical energy. When hard labor is being performed, an excess of fat is instinctively taken. Carbohydrates.—The carbohydrates include the starches, sugars, and cellulose. ' The Starches, though presenting very different appearances under the microscope according to source, are of equal value as foods, and have the same composition. Starch is insoluble in water, but, heated In this group the kyrines may be included. For the present we believe that it will be helpful to retain this term as defined, reserving the expression peptide for the sim- plei compounds of definite structure, such as dipeptides, etc. _ ie peptones are undoubtedly peptides or mixtures of peptides, the latter term being at present used to designate those of definite structure.