290 DR. ROBERTS ON THE DIURNAL 
depress the acidity of the urine? Dr. Bence Jones im- 
putes it to the diversion of the acid present in the blood 
to the stomach for the purposes of digestion. When the 
stomach is empty its ling membrane is neutral, or nearly 
so, and the acid generated in, or thrown into, the blood 
passes off by the skin and kidneys, rendering the urine 
acid; but when food is taken, acid gastric juice is poured 
from the blood vessels into the stomach, and the alkali- 
nity of the blood is consequently raised. This causes the 
kidneys to separate a less acid or even an alkaline pro- 
duct; but when digestion is completed, the gastric acid 
returns to the blood with the chyle, and the urine regains 
its normal reaction. So that the stomach and kidneys 
are antagonistic in their reaction, the former being least 
acid when the latter are most so, and vice versd. So 
plausible an explanation was at once adopted; and it is 
difficult to imagine that it may not have some operation 
in the way supposed, though, as I believe, it must be re- 
jected as the main cause of the alkaline tide. 
From Dr. Beaumont’s twenty-fifth and twenty-sixth ex- 
periments, second series, we are led to conclude that suffi- 
cient gastric juice for the digestion of a meal is poured 
into the stomach within fifteen or twenty minutes after its 
ingestion ; and that in half an hour, or an hour at most, 
the flow of acid into the stomach has ceased and absorp- 
tion of the digested meal commenced. If this be so, the 
reaction of the urine ought to be most depressed within 
an hour or an hour and a half after a meal, instead of 
from two to five hours after. Moreover, how can it be 
explained, on this supposition, that the alkaline tide after 
dinner sets-in an hour or an hour and a half later than 
after breakfast ? 
But, whatever may be thought of the validity of these 
objections, is there not another solution more consonant 
with the facts observed? Is the alkaline tide not the 
