VARIATIONS IN THE ACIDITY OF THE URINE. 273 
XV., support the main conclusion as uniformly as could 
be expected, if it be remembered that the densities were 
taken by a hydrometer, without correction for tempera- 
ture, and not with that care and precision which would 
have been used had it been foreseen that they would 
have been employed for calculating the solids. 
The rise in the hourly discharge of acid from nine to 
eleven and eleven to twelve (eighth, ninth and tenth hours 
after dinner) is, therefore, entirely due to the fact that the 
increased activity of the kidneys, called forth by the meal, 
persists for two or three hours after the blood, and by 
consequence the urine, has recovered its normal reaction. 
So that by taking the solid urine as a basis for calcula- 
tion, two distinct corrections have been shown to be ne- 
cessary in reading the determinations of acidity per hour. 
By the first correction, the apparently doubtful or contra- 
dictory cases, where there was but a slight or no fall in the 
numbers after breakfast, are made to agree satisfactorily 
with the general law; and by the second, the apparent 
~ existence of an acid tide following in a few hours on the 
ebb of the alkaline tide is shown to depend on a fallacy. 
The duration and time-of-setting-in of the alkaline tide 
were both subject to considerable variations from day to 
day, and they differed too for breakfast and dinner. 
Under the term alkaline tide is embraced the whole period 
of depressed acidity, whether the urine at the time was 
alkaline, neutral or only of diminished acidity.* 
The effect of breakfast appeared earlier than that of 
dinner, and was always distinctly perceptible at nine 
* It might be objected to this term, alkaline tide, that it is applied to 
urines which do not become alkaline. But, although in such instances 
the urine does not altogether lose its acidity, there is only a difference 
of degree between such and those in which the urine becomes actually 
alkaline. There is the same movement in both cases; but in the former it 
does not crop out from beneath the surface of the neutral line, whereas in 
the latter it makes itself sensible by a change of reaction. 
