Lectures on the theory and practice of physic (Volume 2).

  • Stokes, William, 1804-1878.
Date:
1842
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Licence: Public Domain Mark

Credit: Lectures on the theory and practice of physic (Volume 2). Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    soluble in its own weight of cold water, and in every proportion in hot water. Urea combines with several acids, but does not neu- tralise them. Alkalies scarcely affect urea at low temperatures, but when it is assailed by heat, they rapidly convert it (together with water) into the carbonate of ammonia. In certain diseases of the kidney, urea exists in the blood in con- siderable quantities, as ascertained by Dr. Christison and others. There are diseases connected both with an excess and a defi- ciency of urea in the urine. Lithic or uric acid, supposed once to be a product of morbid secretion, is now known to be an invariable ingredient of healthy urine ; and present in solution at all ordinary temperatures. If it exists in the blood at all, it is in very small quantity only. Prout supposes it to be combined with ammonia, and not to be secreted in a free state. It is rendered probable by Liebig and Wuhler, that lithic acid is a compound of urea and a substance itself composed of cyanogen and carbonic oxide. The lateritious and pink sediment were supposed by Proust to constitute a peculiar acid, which he named rosaceous; but these have been found to consist essentially of the lithate of ammonia, and, sometimes, of the lithates of soda and lime, in small proportions. They owe their colouring matter partly to the colouring matter of the urine, and partly to the purpurate of ammonia. The colouring matter of the urine consists of yellow principles, more or less acted on by nitric acid, which Prout supposes to be in some way an ingredient of healthy urine. The next and most important form in which lithic acid appears in the urine, is that of lithic acid gravel, the immediate cause of the precipitation of which is the lactic acid, which is generally at this time secreted in excess, either separately, which is comparatively rare, or in a state of combination with urea, which seems to be the rule. The frequent presence of sugar in urine depositing lithic acid gravel and the frequent appearance of lithic acid gravel in slight forms of diabetic disease, are explained by our learning, that the lactate of urea and the saccharate of urea are, in fact, but modi- fications of the same substance, and may be considered as the re- presentatives of gelatin; the lactic acid being, as we have said, only a modification of the saccharine principle. The lithic acid is, on the same authority {Prout), a principle of albuminous origin, and may be readily distinguished by the develop- ment of the purpurate of ammonia, by the aid of the action of the nitric acid and heat. The sulphuric and the phosphoric acids appear to exist in healthy urine in union with soda, potassa, and ammonia, and partly with magnesia and lime. The muriates of potassa and soda occur both in the blood and the urine. Muriatic acid exists only, in the urine, in combination with ammonia. I shall not make any remarks on the otherconstituents of healthy urea, but devoteafewwordstothe foreign substances which are occasionally found in it; and one of which, albumen, has of late become an exceedingly important diagnostic test of certain diseases.