EXAMINATION OF URINE - next proceed to a consideration of the diagnostic points connected with diseases of the urinary organs: our knowledge on this subject is in great measure derived directly from the condition of the urine, and we must therefore inquire with some minuteness into the changes which it undergoes. In doing so we shall find that in very many instances its abnormal states are dependent on diseases of distant organs, by which the function of the kidney merely is interfered with, while no actual change passes on the structure of that organ; but as our object is to ascertain tbe bearing of symptoms upon the condition of the patient, no apology need be offered for bringing together here all these varieties, whether belonging to diabetes, to the Ethic acid diathesis, as it is called, or even simply to dyspepsia ; although it must be understood that they do not rank in a pathological sense as diseases of the urinary organs.
Probably a large field of observation remains open which may at some future period be made available for the discrimination of disease, and the treatment of the patient, in ascertaining the relative amount of the various normal ingredients of the urine; but at present the variations to which they are subject must be left to those who have made chemistry their special study : our attention must be limited to changes which are easily appreciated and readily recognized. Let me only caution the student against what may be called rough-and-ready tests, and deductions based. upon inaccurate inveztigations: it would be well if he knew how to make a quantitative analysis of the different products, because mistakes are continually being made in practice from ignorance on this point, as when, for example, an unusual manifestation of the presence of any ingredient, by precipitation or otherwise, is taken as evidence of its being present in exe,ess--a conclusion which may be true, or may be utterly false. Unfortunately quantitative analysis is exceedingly difficult, but we may at least secure accuracy m the qualitative analysis, and this must never be overlooked : it is exceedingly unwise to attempt to decide on the characters of the urine by boiling it in a spoon over a candle, when we can always carry away a portion and examine it with a test-tube and a spirit-lamp. Most especially in commencing the
study it is important to obtain accurate results; if this be attended to in the first instance, it will give a much greater readiness in subsequent investigations; and no opportunity of making obser vations should be lost, until this accuracy and readiness are at tained. However definite the rules laid down, fallacies can only be avoided by frequent practice.
The chemical tests in constant use are the colored papers for ascertaining the acid or alkaline reaction of the urine, the urinometer for determining its specific gravity, and the obsetvation of the changes produced by the addition of acid and alkali and the application of heat. Before further it may be well to say a few words on each of these points.
The urine is naturally acid under ordinary circumstances, and care must be taken in pronouncing it unusually so from the effect produced on the teat paper, because all test-papers are not alike; one becomes very much reddened by acidity which only slightly alters another. In conditions of slkalescence it is important to have the test-paper as delicate as possible, because the re action is frequently very weak. Alkalescence due to ammonia, if not distin guished by the smell, may be readily recognised by the action of heat, which the volatile alkali, and restores-the color of the paper.
The urine taken for the purpose of determining the specific gravity should be, if possible, obtained from a large quantity ; each time that urine is passed in the twenty-four hours it varies somewhat in specific gravity, and, as an isolated fact, its increase or decrease is of little value unless it be found per sistent on repeated trials.