266 DR. ROBERTS ON THE DIURNAL 
vegetables; in the sweet and subacid fruits of our own 
and tropical climates — in all these, may be found repre- 
sentatives of the albuminous, oleaginous and saccharine 
groups of alimentary substances, together with certain 
saline ingredients — phosphates, sulphates, chlorides and 
carbonates, having for bases soda, potash, lime and mag- 
nesia — whose universal presence sufficiently attests the 
essential importance of their functions. 
Nevertheless the wide differences of proportion which 
are known to exist in the admixture of the organic and 
inorganic substances in various articles of diet, and espe- 
cially in the contrasted classes of animal and vegetable 
foods, prepare us to expect that in the final products of 
the vital operations there will be found certain peculiari- 
ties attributable to the nature of the aliment. One of 
these is the reaction of the urine, which is notoriously 
dissimilar in carnivorous and herbivorous creatures, being 
acid in the former and alkaline in the latter. And this 
difference has been universally laid to the account of the 
food of the two classes. 
The urine of the herbivora is alkaline, it is asserted, 
because they feed upon matter rich in alkaline carbonates, 
citrates and tartrates, all of which appear in the urine as 
carbonates. And it has been shown that when these 
creatures are made to fast, their urine becomes acid. 
Dr. Cl. Bernard* was able to trace still more decisively 
the connection between the reaction of the urine and the 
nature of the food. He found that when rabbits (whose 
urine is normally alkaline) were fed for some time on an 
exclusively animal diet, they passed an acid urine; and 
that its alkalinity was not restored until a vegetable diet 
was substituted. Dogs also, when restricted to a vege- 
table fare, secreted an alkaline urine, turbid from depo- 
sition of phosphates; but when restored to animal flesh 
* Comptes Rendus, 1846, tom, 22, p. 534. 
