248 DR. ROBERTS ON THE DIURNAL 
On the first day a slight luncheon, consisting of two 
thin pieces of bread and butter and a glass of water was 
taken at two. This accounts for the slow degrees by 
which the acidity recovered its ordinary level after break- 
fast. 
About a pint of porter was taken between nine and 
eleven on the first night, and some bread and butter with 
tea between nine and ten on the second night. For this 
reason the urines passed after ten o’clock, on the first and 
second nights, are not reckoned in the table of means. 
Previous to these four days the condition of the urine had 
been examined at short intervals on five other days after 
breakfast, and on four days after dinner. On each day 
the urime became alkaline after dinner. After breakfast 
it became alkaline three times; but remained acid, in a 
diminished degree however, on the remaining two days. 
The times of change from acid to alkaline, and back 
again from alkaline to acid, having now been ascertained 
with tolerable certainty, it was thought unnecessary to 
carry out so rigidly the very laborious plan of hourly ob- 
servation throughout the entire day. In the succeeding 
experiments, therefore, hourly observations were only 
made at the critical periods, when the reaction was oscil- 
lating; but when the acidity was steadily rising, or had 
attained its usual level, observations were made every 
two hours. By this modification the experiments could 
be carried on with comparative ease, and continued for 
several consecutive days. 
The effect of mixed food was again subjected to obser- 
vation during seven days, all consecutive but one. Two 
meals a day were taken, and no alcoholic drinks. 
