Licence: Public Domain Mark
Credit: A manual of veterinary physiology / by F. Smith. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![duction of entirely new substances. A common illustration of ferment activity is the yeast-plant, which is capable of producing out of sugar, alcohol and carbonic acid ; its func- tion is due to a living cell, and such a ferment is described as organized ; micro-organisms, such as are found in the intestinal canal and other places, which are capable of pro- ducing great changes in the constitution of organic fluids, are also classed as organized, for example, the lactic acid ferment or bacillus, and the bacillus splitting up urea into carbonate of ammonia, etc. In the body another class of ferment exists, which, as it does not depend upon a living cell, is described as unorganized or soluble ; such is the ferment which converts starch into sugar, the so-called amylolytic; the proteolytic or ferment converting proteids into peptones; the fat-splitting ferment, which breaks up fat into glycerin and fatty acids ; the milk-curdling ferment of the fourth stomach of the calf; the fibrin-forming fer- ment of the blood, etc.: all these can by appropriate means be isolated from the various tissues which produce them. Almost all dead tissues and organic fluids may act as. starch-converting ferments. Both the unorganized and organized ferments agree in so far as their general action is concerned. All of them are destroyed by raising the fluids containing them to a certain temperature; none of them appear to suffer, that is to be worn out or exhausted, by the amount of work they per- form, and in consequence in each case a small quantity of them will produce as great an effect as a larger quantity. The Pigments of the body are classed as proteids ; com- ])aratively little is known about them, thougli they are Avidely distributed and perform important functions. The best known animal pigment is haemoglobin, the red colouring matter of the blood ; it is of a proteid nature, yet crystalliz- able, and it also contains iron; it acts as an oxygen carrier, and is often spoken of as a respiratory pigment; it has several derivatives (see Blood), which supply the colouring matter of the bile, urine, and fa3ces. The next pigment widely distributed is the black pigment of the body, or](https://iiif.wellcomecollection.org/image/b21933480_0031.jp2/full/800%2C/0/default.jpg)
