280 DR. ROBERTS ON THE DIURNAL 
less there are secret causes of unequal action in the animal 
system of so subtle a nature as to be altogether beyond 
our present powers of appreciation. I would suggest, 
however, that the state of the body in respect to repose 
and exercise, and the external temperature, probably exert 
an important influence. 
Muscular juice is highly acid, and its quantity is, in all 
likelihood, greatly increased by exercise; and it seems 
not improbable, as Vogel has suggested, that the degree 
of acidity of the urine has some connection with the 
quantity of this acid of muscle thrown into the blood, 
and so through the kidneys out of the body. 
The external temperature, too, by quickening or re- 
tarding the cutaneous transpiration and the respiratory 
fuuction, may affect the amount of acid circulating and 
generated in the blood. 
Differences in the nature of the food, especially as re- 
gards the proportion of earthy and alkaline phosphates, 
may almost with certainty be named as operative in caus- 
ing differences in the effects of different meals on the 
reaction of the urine. 
This and other matters connected with this part of the 
subject will come under discussion again when the inquiry 
is entered on — Why should a meal depress the acidity of 
the urine ? 
The amount of free acid separated in the course of the 
twenty-four hours was fouud, on an average of nineteen 
days, to be sufficient to neutralise 14°10 grains of dried 
carbonate of soda, or an average of 0°58 grains per hour. 
The maximum quantity was 22°34, and occurred under a 
purely animal diet ; the minimum was 5-90 under a mixed 
diet. Some days were found exhibiting throughout a 
feeble acidity; others a high acidity, quite independently 
of the nature of the diet. The average amounts of acid per 
a oe 
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