READJUSTMENTS OF REGULATION 39 
expense of the normal elimination of urea. Urea 
CO(NH.,), is a nitrogenous body of neutral reactions 
in the form of which by far the greater part of the 
combined nitrogen passing through the body is elimi- 
nated. In acid poisoning the combined nitrogen goes 
more and more into the form of ammonia (NH,), 
which, in virtue of its alkaline reaction when in solu- 
tion, combines with acids and thus neutralises them. 
Even under average normal conditions in man the 
quantity of ammonia eliminated in the urine is about 
sufficient to neutralise the large quantity of sulphuric 
acid formed by the oxidation of the sulphur of 
albuminous substances ; and with an alkaline diet this 
ammonia practically disappears from the urine. In 
the Strassburg laboratory it was also discovered that 
ammonia salts are converted into urea in the liver. 
We have now every reason to believe that ammonia 
is formed in large quantities in the intestine by the 
breaking down under ferment action of albuminous 
compounds. This ammonia is carried straight to the 
liver by the portal circulation, and there converted 
under ordinary conditions almost entirely into urea. 
But the liver appears to leave unconverted any am- 
monia needed to regulate the reaction of the blood, 
and the minutest deviations in reaction serve to regu- 
late this process. Hence in the ratio between ammonia 
and total combined nitrogen in the urine we have a 
valuable index of any tendency towards acidity or 
alkalinity of the blood, though the composition of the 
alveolar air is a still more direct index. 
Another known means of regulation is by the kid- 
