THE CHEMISTRY OF THE URINE. 
By F. Gowlaxd Hopkins. 
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 ; (<j) 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 
