THE CHEMISTEY OF THE URINE. 



BY F. GOWLAND HOPKINS. 



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CONTENTS : Introductory Quantitative Composition of Urine, p. 572 Variations 

 in its Amount and Specific Gravity, p. 573 Its Chemical Reaction, p. 574 

 The Nitrogenous Constituents : (a) Total Nitrogen, p. 580 ; (b) Urea, p. 581 ; 

 (c) Ammonia, p. 585 ; (d) Uric Acid, p. 586 ; (e) Xanthin Bases, p. 596 ; (/) 

 Creatinin, p. 598 ; (g) Hippuric Acid, p. 600 ; (h) Amido- Acids, p. 602 Pro- 

 teids, p. 603 The Aromatic Substances, p. 605 The Carbohydrates, p. 607 

 Glycuronic Acid and its Conjugated Compounds, p. 613 Oxalic Acid, p. 614 

 Acids and Oxyacids of the Fatty Series, p. 615 Colour of the Urine and the 

 Chemistry of its Pigments, p. 616: (a) The Preformed Pigments of Normal 

 Urine, p." 618 ; (b) Chromogenic Substances, p. 626 ; (c) The Pigmentation of 

 Pathological Urine, p. 628 The Inorganic Constituents, p. 630 General 

 Characteristics of the Organic Urinary Compounds, p. 635 Comparative 

 Chemistry of the Urine, p. 637. 



General considerations. The chemical study of the urine gains its 

 chief importance from the light which it throws upon the processes of 

 metabolism. It is concerned mainly with a consideration of the nature 

 and amount of the various metabolic end-products, normal or patho- 

 logical, which converge into and appear together in the highly complex 

 excretion of the kidneys. 



The great importance of this point of view has led to perhaps undue 

 neglect of a second aspect of the subject the consideration of the 

 renal excretion as a complex whole ; as a chemical fluid with individual 

 characters of its own ; characters which are not to be foretold from a 

 knowledge of the nature and amount of each constituent considered 

 separately, but require for their explanation the further consideration of 

 the mutual effects of the constituents one upon another, as they exist 

 side by side in solution. 



This study of the properties of the urine as a whole must be pursued 

 if we are to understand with exactness the nature of the processes which 

 go on in the kidney, and if we wish to interpret aright the ultimate 

 behaviour of any given type of urine while in the urinary passages, or 

 after it has left the body. 



But while the first-mentioned line of study requires in the main the 

 services only of analysis the earliest and best understood of the weapons 

 of chemistry the second depends upon our more recently won, and as 

 yet very incomplete, knowledge of chemical statics, and of the conditions 

 of equilibrium in salt solutions. 



All the chief proximate constituents of normal urine exhibit either 

 basic or acid characters. Indifferent or " neutral " substances are norm- 

 ally either absent, or present in minimal amount. The bases and acids 

 present necessarily enter into more or less stable combinations, and it 



