VARIATIONS IN THE ACIDITY OF THE URINE. 289 
oftener than about five times in the twenty-four hours ; 
and by comparing the times of the meals with the times of 
micturition, it becomes evident that it was impossible for 
him to obtain results other than nugatory. The urines he 
examined were mixed urines, and he did not in any wise 
isolate the secretion at the critical periods. 
The same objection applies to the observations con- 
ducted under the supervision of Vogel. The urines were 
collected during three periods— namely between breakfast 
and dinner (morning urine), between dinner and evening 
(afternoon urine), and during the hours of night. All such 
urines would be acid mixtures ; but it by no means follows 
that they did not pass through an alkaline state, possibly 
even of some hours duration. 
So true is it that the existence of the alkaline tide may 
be concealed for an indefinite time, even from those who 
are in the constant habit of observing the state of the urine, 
unless the urinary product be, as it were, analysed by fre- 
quent micturitions, that the urine of the subject of these 
experiments, though under close observation for some 
years, was not once known to have departed from its usual 
acid reaction; and it took me almost by surprise to find 
the phenomena of the alkaline tide so strongly and so 
remarkably pronounced after such long and effectual 
concealment. 
A second circumstance, which must be borne in mind, 
is the remote influence of meals. As already fully ex- 
plained, this remote effect of a previous meal frequently 
altogether masks the immediate effect of a recent one; 
and this statement seems especially to apply to the effect 
of supper on the succeeding breakfast. For this reason it 
is well, in order to obtain distinct results, to fast for eight 
or ten hours, or more if night intervene, before taking the 
meal whose effect it is wished to observe. 
Finally, we come to the inquiry: Why should a meal 
