270 DR. ROBERTS ON THE DIURNAL 
of acid. For example, on the 25th of January (Table X.), 
the hourly separation of acid before breakfast was 1-08. 
During the first hour after breakfast it rose to 1:25; but if 
the solid matters be brought into consideration, it is found 
that there is here in reality a depression, instead of an 
elevation, of the acidity. At the former period the solids 
had a per-centage of acid of 3°81; whereas at the latter, 
the per-centage had declined to 3:17. 
I have been thus at pains to prove that the evidence of 
the first set of experiments on vegetable food is unequi- 
vocal as to the depressing effect of vegetable food on the 
reaction of the urine, not because other proof was want- 
ing —the second set abundantly supplies that — but in 
order to uphold the conclusion contended for, that all 
the observations on the individual under experiment were 
perfectly concurrent; and that the law, so far as he was 
concerned, came out absolute and without exception, that 
food lowered the acid reaction of the urine. 
There is considerable advantage in comparing the oscil- 
lations of the urinary free acid with the oscillations in the 
hourly discharge of solid urine. It is from this point of 
view that we can best see the relations of the former to 
the state of the blood. It is not necessary here to go into 
the proof that the degree of alkalinity of the blood regu- 
lates strictly the rising and falling acidity of the urine. 
By adding to the alkalescence of the blood through artifi- 
cial means, as by exhibiting caustic or carbonated alkalies 
internally, we are able to depress in corresponding pro- 
portion the acidity of the urine. On the other hand, also, 
by exhibiting acid (although this seems less readily ac- 
complished) we can similarly heighten the reaction. 
By taking the solid urine as a standard of comparison, 
we avoid two fallacies which respectively affect the deter- 
minations per 1000 parts and the determinations per hour. 
We escape, in the first place, oscillations arising from mere 
