292 DR. ROBERTS ON THE DIURNAL 
by the kidneys; and as absorption goes forward and in- 
creases, the acidity of the urine diminishes more and more. 
It is nevertheless true that the subsidence of the alkaline 
tide is not synchronous with the cessation of absorption, 
for we have seen that the passage of food into the blood 
appears at its highest activity when the alkaline tide is 
beginning to ebb. This want of coincidence appears, 
prima facie, to militate against the solution here offered ; 
but it may be explained in two ways. Either it arises 
from the phosphatic salts being absorbed with more cele- 
rity than the rest of the food, and producing their effect 
before the other materials are all taken up; or, more pro- 
bably, it depeuds on the increased absorption of oxygen 
by respiration, already noticed as occurring after a meal, 
which, after the lapse of five or six hours, by generating 
acid, counteracts the contrary effect of the food—in other 
words, from the remote effect of a meal overlapping the 
immediate effect. 
If this solution be admitted, it brings all ordinary food 
into the same category with sub-acid fruits, which have 
long been acknowledged to possess the power, in virtue of 
their saline constituents, of rendering the urine alkaline ; 
the only difference being that in the latter the effect is 
produced by salts, which become carbonates in the blood, 
and in the former by basic phosphates, which pass as such 
into the urine.* 
* It must not for a moment be supposed that the urine is never alkaline 
(from fixed alkali) except after food. The urine not unfrequently loses its 
acid reaction in disease, independently of food, and presents to all appear- 
ance the characters of the urine of the alkaline tide after a meal. Ihave 
observed this character of the secretion repeatedly in the debilitated and — 
ansemic condition which sometimes follows chronic subacute gout and 
obstinate subacute articular rheumatism; also in the course of some other 
protracted and exhaustive diseases that induce a chlorotic or spanemic 
state; of which perhaps the most common is a certain form of atonic dys- 
pepsia. In such cases the urine may be alkaline all the day through, though 
. '. a, tk ee 
