330 



Prof. F. Smith. 



[June 20, 



calculated until the inquiry was completed ; it was then observed that 

 the composition of healthy horse's urine will vary within wide limits, 

 and that even from day to day the same horse will excrete a fluid of 

 very varying composition, though his condition of diet, &c, remains 

 absolutely the same. I am not prepared at present to offer an ex- 

 planation of this condition, which so seriously affects my tables of 

 mean results as to render them only approximately true. 



Physical Characters of the Urine. 



Turbidity. — The normal urine is invariably turbid, due to the 

 suspension of the carbonates of lime and magnesia which precipitate 

 themselves in still greater abundance as the urine cools and stands, 

 and undergoes ammoniacal fermentation. 



The amount of salts in suspension is in some cases remarkable, the 

 most common being the carbonates of lime and magnesia, which 

 I have in the majority of my analyses estimated separately as sus- 

 pended lime and magnesia. Boiling the urine by driving off C0 2 

 precipitates more of the lime salts. In one or two cases after the 

 urine had stood some days, a hard scum, quite crystalline, has formed 

 on its surface ; this has consisted of crystals of lime carbonate. Only 

 once in ninety-six observations had I a perfectly clear urine presented 

 for examination, a urine which threw down no deposit on cooling and 

 standing, and was in most of its physical features closely allied to 

 human urine. 



Smell. — Perfectly fresh urine has a faint but distinctly ammoniacal 

 smell ; the fluid which represents the twenty-four hours' excretion is 

 always powerfully ammoniacal. This latter creates a difficulty with 

 regard to the determination of urea, for it is impossible to say how 

 much of the ammonia is due to changes in the urea, and how much is 

 preformed ammonia. I have always felt this a trouble throughout 

 the work, but will later explain how I have endeavoured to over- 

 come it. 



Reaction. — This is always alkaline, sometimes faintly, but in the 

 majority of cases strongly so. The alkalinity shown by test papers 

 is produced by a fixed and by a volatile substance — the volatile is the 

 ammonia, the fixed is probably a salt of potash. It is obvious that 

 the amount of volatile alkalinity present depends greatly upon the 

 time of year, the condition of the urine (those containing most mucus 

 containing most volatile alkalinity), and the length of time which 

 has elapsed before the estimation is made. As remarked in the last 

 paragraph, how much of the volatile alkalinity in urine twenty-four 

 hours old is due to preformed ammonia, and how much to the 

 ammonia formed at the expense of the urea, it is difficult to determine ; 

 it is probable, however, that the preformed ammonia in urine is given 



