URINE. 199 



tube, and allow it to stand for some hours. Decant the upper 

 6-7ths, pour a portion of the remainder into a watch-glass, and 

 gently warm it over a lamp ; in a few seconds the heat will have 

 dissolved any urate of ammonia that may be present, and will 

 (by rendering the fluid specifically lighter) induce the deposition 

 of the crystals of oxalate of lime. Having allowed the urine to 

 repose for a minute or two, remove the greater portion of the 

 fluid with a pipette, and replace it by distilled water. A white 

 powder, often of a glistening appearance, will now become 

 visible, and this, under a microscope furnished with a half-inch 

 object-glass, will be found to consist of crystals of oxalate of lime 

 in beautifully-formed transparent octohedra,with sharply-defined 

 edges and angles. (Fig. 36 a.) This process is the most satis- 

 factory, and, after a little experience, can be performed in a few 

 minutes. But even this may be avoided by placing a drop of 

 the lowermost stratum of the urine on a plate of glass, placing 

 over it a fragment of thin glass or mica, and then submitting 

 it to the microscope ; the crystals diffused through the fluid 

 becoming very beautifully distinct. In this way, however, it is 

 obvious that very much fewer are submitted to examination than 

 by the former process. This salt never (or scarcely ever) subsides 

 to form a distinct deposit; remaining for days diffused through 

 the fluid, even when present in so large a quantity that each drop 

 of the urine, when placed under the microscope, is found loaded 

 with the crystals. A large quantity of the oxalate, when present, 

 may escape the eye, in consequence of its refractive power ap- 

 proaching that of the urine; for whenever we meet with a 

 specimen in which the salt has partially subsided, and replace 

 the decanted urine by distilled water, the crystals often become 

 readily perceptible to the unaided eye, resembling so many 

 glistening points in the fluid. 



The crystals of the oxalate, when collected in a watch-glass 

 in the manner above directed, are unaltered by boiling either 

 in acetic acid or solution of potash. In nitric acid they readily 

 dissolve without effervescing, and the act of solution can be 

 observed with the microscope. When the oxalate is allowed to 

 dry on a plate of glass, and then examined, each crystal re- 

 sembles two concentric cubes with their angles and sides 

 opposed; the inner transparent and the outer black, so that 

 each resembles a translucent cube set in a black frame. (Fig. 



