202 THE SECRETIONS: 



of ammonia ; its insolubility in strong acetic acid prevents it 

 from being mistaken for earthy phosphates. The best cha- 

 racter of cystin is its ready solubility in ammonia, mere agita- 

 tion of some of the deposit with liquor ammonise being sufficient 

 to dissolve it, and a few drops of the solution evaporated on a 

 slip of glass leaving six-sided tables of cystin. (See fig. 32 a.) 

 A certain portion of cystin exists in a state of solution in the 

 urine, as the addition of acetic acid always precipitates a small 

 quantity. Urine containing cystin usually develops a peculiar 

 odour resembling that of the sweet-briar, and often exhibits a 

 peculiar greenish tint. (See Urinary Deposits, p. 111.)] 



13. Pus. 



Pus is not easily detected in the urine, especially when a 

 small quantity is mixed with a much larger amount of mucus. 

 I must refer to what has been already stated in page 100 re- 

 garding the distinctions between pus and mucus ; it must at 

 the same time be remembered that the mucus of the bladder 

 differs in its properties from the bronchial mucus, and is less 

 easily distinguished by the naked eye from pus. Urine con- 

 taining pus may have an acid, neutral, or (and that not un- 

 commonly) an alkaline reaction; at least it exhibits in most 

 cases a strong tendency to the development of ammonia. The 

 colour and amount of solid constituents are subject, according 

 to Willis, to great variations. There is only one propertj^ of 

 purulent urine that can be considered specific, and that is the 

 invariable presence of albumen; too much stress must not, 

 however, be laid upon this point, since urine is frequently albu- 

 minous without containing a single particle of pus, and we may 

 very easily mistake albuminous urine containg mucus for puru- 

 lent urine. In order to detect the presence of pus with the 

 greatest degree of certainty, the urine should be analysed as 

 soon as it is discharged; it is then turbid, and very soon de- 

 posits a sediment, which, on the least motion of the glass, mixes 

 with the fluid, and is again as quickly deposited. It forms an 

 uniform substratum of a yellow, pale yellow-green, or yellowish- 

 white colour, in which the presence of blood may also some- 

 times be recognized. On examining the sediment with the 

 microscope, we find that it consists of pus-globules (fig. 17), 

 which, by inclining the stage of the microscope, may be readily 

 caused to move ; and if the colour should lead us to infer the 



