VARIATIONS IN THE ACIDITY OF THE URINE. 281 
twenty-four hours for the different sets were: mixed diet 
(Tables I. and III.), 14-21 and 10°30; purely vegetable diet 
(Table XI.), 15°36; and purely animal food (Table XV.), 
18:03. These numbers show that the daily amount of acid 
eliminated by the kidneys was not much or uniformly 
affected by the nature of the food. The smallest numbers 
occurred under mixed food; but I am not disposed to at- 
tribute this to the nature of the food so much as to other 
circumstances, inasmuch as on some of the days of mixed 
food the acidity ruled unusually high, but the averages 
(especially of those of Table III.) were greatly reduced by 
one or two days of very low acidity. 
The degree of acidity per 1000 grains is of more impor- 
tance, practically, than the amount per hour, inasmuch as 
the occurrence of urinary deposits depends on it. If no 
liquids were taken, the degree of acidity after the pass- 
ing away of the alkaline tide, gradually increased until 
food was again taken. The highest acidity, therefore, was 
always found after the longest fasting, or just before break- 
fast and dinner. Between seven and eight in the morning 
the urine was uniformly found excessively acid, invariably 
depositing abundance of urates on cooling. The night 
urine likewise, except when liquids were taken on going to 
bed, was highly acid and sedimentary. It may be easily 
conceived, therefore, that this is the period most favour- 
able to the formation of renal and vesical concretions. 
The urine flows slowly aud rests for a lengthened period 
in the bladder, while its excessive acidity and concentra- 
tion diminish its solvent powers over oxalate of lime, uric 
acid and the urates — the three substances most liable to 
unuatural precipitation. 
When no liquids were taken before going to bed the 
urine of sleep had an acidity varying from 1°50 to 2°16 per 
1000. In the morning, before breakfast the numbers ran 
from 1°50 to 2:80 and 3:00, rising on one occasion to 3°68 
