A text-book of physiological chemistry for students of medicine / by John H. Long.

  • John Harper Long
Date:
1909
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of physiological chemistry for students of medicine / by John H. Long. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    appear to be aldehyde bodies and as such have reducing power. They react also with phenyl hydrazine and yield osazones, which, however, are not easily purified, because of their solubility. The dextrins have a slightly sweetish taste and all show a specific rotation about [a]D = -f- 1960. Beyond the empirical formula C6H10O5 it is not possible to go in describing the constitution of these bodies. The natural vegetable gums are often mixtures of several sub- stances, and but few of them have been studied. Gum arabic and gum Senegal are the potassium and calcium salts of arabic acid to which the formula (C6H10O5)2 + H20 is given. On treatment with weak sulphuric acid both arabinose and galactose appear to be formed. Agar-agar is said to yield lactose and then galactose, while cherry gum yields arabinose. Cellulose. The cell walls of vegetable substances consist of cellu- lose mixed always with related compounds of which a body called lignin is the most important. The cellulose resists the action of strong oxidizing or other agents much more perfectly than do' the accom- panying bodies, and may therefore be freed from them by various treatments. In washed Swedish filter paper we have an illustration of nearly pure cellulose, as all the other bodies in the original fibers have been removed by the bleaching and washing processes to which the raw material was subjected in the manufacture of the paper. A pure cellulose paper may be made from wood also, but only by more com- plicated operations. The pure cellulose is characterized by insolubility in water, weak acids, alkalies, alcohol or ether. It may be dissolved rather readily in a solution known as Schweitzer's reagent and by prolonged di- gestion with acids is converted into hexoses and pentoses. The natural celluloses may be divided roughly into three groups: (a) those which resist hydrolytic action very perfectly and are not capable of serving as foodstuffs for any animals; in this group we have linen and cotton fibers, hemp, China grass, etc. (b) Those which are less resistant to hydrolytic action and which contain active CO groups. These bodies may be called oxycelluloses; they yield also furfuraldehyde by distillation with hydrochloric acid. In this group we have the mass of the material found in the fundamental tissues of flowering plants, and a large part of ordinary woody tissue. This lignified tissue is made up of compound celluloses or lignocelluloses from which the cellulose proper may be isolated in a variety of ways. Some of the bodies in this sroup are partly digestible and have some value as foods for the herbivora. (c) In this third group we have
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