824 
DR. SMITH ON THE ELIMINATION 
occasions, any material change in the quantity of food taken ; for aperients and emetics 
were had recourse to, and relief was soon obtained. 
[The years 1861 and 1862, Table I. p. 759 et seq^., offer numerous records in which 
the quantity of urea eliminated was temporarily lessened under the influence of oppres- 
sive weather or of internal conditions, causing headache and general malaise. Such are 
May 14 and 21, and 28 to 31 ; June 14 ; July 2 to 5 and 20 ; October 8 ; November 3 
and 4, 6 and 8; December 6 to 10, 1861; and January 26, 1862.] 
The effect of purging over the elimination of urea was commonly inconsiderable ; but 
in one instance there was a great diminution of both urea and urine. 
10. Relation of Urea and Carhonio Acid. 
Scarcely any observations have hitherto been made in reference to the relation of urea 
and carbonic acid ; but Bechee (Henle’s ‘ Zeits.’ 1855) observed a general relation exist- 
ing between these two excretions, and particularly in their relation to food, but the two 
did not move in parallel lines. My inquiries into the evolution of carbonic acid and 
urea enable me to show some of their relations, as follows : — 
1. In both alike the period of production is not identical with that of elimination. 
Tea and coffee cause a larger elimination of carbon than they supply ; and in a paper 
published in the ‘Philosophical Magazine’ for December 1859, I showed it to be pro- 
bable that the immediate action of all food is elimination, whilst the act of production 
is more remote. Hence carbonic acid may accumulate to a certain point, and be dis- 
charged on the application of an efficient cause. So, in like manner, water alone largely 
eliminates urea, and therefore urea must have accumulated, unless we admit it to be 
possible that it promotes the production of urea by increasing metamorphosis of tissue. 
2. AYater has a relation to the elimination of urea analogous to that of air in the 
elimination of carbonic acid, and an increase of both will equally cause an increase in 
the elimination. 
3. The progression in the rate of hourly excretion of both substances after food is 
very similar, in so far that the largest excretion follows the breakfast and the tea meals, 
and the least follows the early dinner ; but the proportionate excretion of urea in the 
middle hours of the day is less than that of carbonic acid. In both the lowest rate 
occurs in the night. 
4. I cannot contrast the effect of season upon these excretions with certainty, since 
the experiments in reference to carbonic acid were limited to the excretion in the 
absence of food and exertion, whilst those on urea extended over the whole day, and 
comprised the whole influence of food and exertion. Hence these are, perhaps, not 
parallel conditions. Season lessens the production of carbonic acid before breakfast as 
the summer advances, and the greatest emission occurs in the spring and winter ; but 
the production of urea with ordinary food and exertion increases with the summer, and 
is the least in the cold season. 
5. Temperature, as it increases, lessens the production of carbonic acid, and lessens 
