256 PHYSIOLOGICAL CHEMISTRY. 



ordinarily free frorn turbidity. Permanently turbid urines ordinar- 

 ily arise from pathological conditions. 



Odor. The odor of normal urine is of a faint, aromatic type. 

 The bodies to which this odor is due are not well known, but it is 

 claimed by some investigators to be due, at least in part, to the 

 presence of minute amounts of certain volatile organic acids. 

 When the urine undergoes decomposition, e. g., in alkaline fermen- 

 tation a very unpleasant ammoniacal odor is evolved. All urines 

 are subject to such decomposition if allowed to stand for a suffi- 

 ciently long time. Under normal conditions the urine very often 

 possesses a peculiar odor due to the ingestion of some certain drug 

 or vegetable. For instance, cubebs, copaiba, myrtol, saffron, tolu 

 and turpentine each imparts a somewhat specific odor to the urine. 

 After the ingestion of asparagus, the urine also possesses a typical 

 odor. 



Frequency of Urination. The frequency of urination varies 

 greatly in different individuals but in general is dependent upon the 

 amount of fluid in the bladder. In pathological conditions an inflam- 

 matory affection of the urinary tract or any disturbance of the in- 

 nervation of the bladder will influence the frequency. Affections 

 of the spinal cord which lead to an increased irritability of the blad- 

 der or a weakening of the sphincter will result in increasing the fre- 

 quency of urination. 



Reaction. The mixed twenty-four hour urinary excretion of a 

 normal individual ordinarily possesses an acid reaction to litmus. 

 This acidity is now believed to be due to the presence of various 

 acidic radicals and not to the presence of sodium di-hydrogen phos- 

 phate as was formerly held (see Phosphates, p. 299). This con- 

 clusion is reinforced by the observation that urine may be divided 

 into two portions, one part consisting almost entirely of inorganic 

 matter, including practically all of the phosphates and having an 

 alkaline reaction, the other containing practically all of the organic 

 substances and no phosphates and having an acid reaction. The 

 acidity imparted to the urine by any particular acid depends entirely 

 upon the extent to which the acid is dissociable, since it is the hy- 

 drogen ion which is responsible for the acid reaction. 



The composition of the food is perhaps the most important factor 

 in determining the reaction of the urine. The reaction ordinarily 

 varies considerably according to the time of day the urine is passed. 

 For instance for a variable length of time after a meal the urine 

 may be neutral or even alkaline in reaction to litmus, owing to the 



