A Text-book of medical practice for practitioners and students / edited by William Bain.
- Date:
- 1904
Licence: In copyright
Credit: A Text-book of medical practice for practitioners and students / edited by William Bain. Source: Wellcome Collection.
Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.
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![Fats. These bodies are compounds of glycerine with fatty acids and therefore contain C, H and O only. They are found in all tissues and form the main bulk of fatty tissue. The fatty acids present in them belong to one or other of the two first series of the open-chain carbon compounds, the paraffins and the olefines. Glycerine is a triatomic alcohol and can therefore combine with tliree fatty acid radicles. The three chief fats found in the body are stearin, palmitin and olein, which are built up from the three fatty acids, stearic, C15H31. COOH ; palmitic, C17H,,. COOH, and oleic, CnHg.,. COOH, respectively. The two former belong to the parafhn, the latter to the olefine series. Thus, for instance, palmitin has the formula C3H5. (CnH^g. 000)3, and similarly for the other fats. In milk, fats con- taining fatty acids lower in the series are present. Thus acids that may be present are : butyric, C3H7. COOH ; caproic, C4HB. COOH, and caprylic, C7H15. COOH. Fats may also vary in that they may contain different fatty acids combined to the same glycerine molecule, so that we may find one butyric acid associated with two stearic acid molecules, etc. The fats have melting points which rise with the number of carbon atoms they contain. Lecithin.—This is a fat of high melting point, which is universally distributed through the body. It occurs in especially large amounts in the white matter of the nervous system. It is excreted in the bile. It is a fat in which two of the acid radicles are stearic acid, the other being phosphoric acid in which one of the acid hydrogens is replaced by choline. Like the fats it is easily soluble in ether or hot alcohol. It also dissolves in cold alcohol and in fats. It is soluble to some extent in a solution of bile salts. Carbohydbates. These substances are all compounds of C, H and O, in which the number of hydrogen atoms is double the number of oxygen atoms, as in water. They are especially character- istic of vegetable tissues and therefore form a most important ingredient of our main food- stufis. At any given time the amount of carbohydrate present in the tissues of an animal is quite small. They are divisible into mono-saccharides, di-saccharides and poly-sac- charides. 1, Monosaccharides. These are all polyatomic alcohols of the open chain carbon compounds, in which one of the carbons has been further oxidised to form a ketone or aldehyde group. They are to be divided, according to the number of carbon atoms they contain, into trioses, pentoses, hexoses, etc., and are all given the termination -ose. The only ones we need consider here are the hexoses, for they are the carbohydrates with which the body mainly has to deal. These are of many varieties according to the position of the ketone or aldehyde carbon in the chain. Dextrose, for instance, is an aldehyde, CH2OH . (CHOH)^. CHO. Levulose, on the other hand, is a ketcme, CH^OH . (CH0H)3. CO . CH^OH. Apart from this difference they show varieties according to the configuration of the side chains at- tached to the several carbon atoms and, owing to the asymmetric structure they possess, for each structural formula there may be three sugars. Thus, one will rotate the plane of p(jlarised light to the right, another to the left and the third will be inactive. They are soluble in water and being aldehydes or ketones, possess strong reducing powers. A further important reaction which they give is the formation of an osazone when treated with phenylhydrazin in the presence of an acid. The osazones are of importance m this connection, for they possess definite crystalline form and melting point, so that, by them, the variety of hexose present in a given solution may be determined. Many ot the hexoses are attacked hy yeast, which converts them into alcohol and carbonic acid. The most important are the following :— , ^ j 4.- t Dextrose.—Grape-sugar is found in small amounts in the blood and many tissue_s ot the body. It is the form of sugar into which most carbohydrates are converted before they are admitted to the blood. It occurs in honey, in grapes and in various other fruits. Levulose This is also known as fruit-sugar and occurs in honey and m most truits. It is aim formed, together with an e(]ual quantity of dextrose, by the hydrolysis of cane- sugar. It rotates the plane of polarised light to the left. r . (ialactose.-^rhis is obtained together with an equal number of molecules of dextrose by the inversion of milk-sugar. It rotates the plane of polarised light to the right. 2. Di-sacchdrides. The di-saccharides are to be regarded as compounds formed by uniting two mono- saccharide molecules to one another with the elimination of one mo ecule of -^^^'l' J-^^^ general fornmla is therefore C,,H,^0„. On hydrolysis they split up again into two mono-saccharides. The most important are cane-sugar, maltose and lactose.](https://iiif.wellcomecollection.org/image/b21510167_0054.jp2/full/800%2C/0/default.jpg)
