6

of one student and one durwan. These limits practically cover the variations seen
in the daily analyses also.

       The average specific gravity over the whole series works out to about 1013,
being slightly higher than this for the students alone, viz., 1015.

       We therefore find that, although a much larger proportion of the fluids got
rid of from the body goes by the skin in tropical climates than in Europe, still
the excretion of the total solids as measured by the specific gravity—also by
the lowering of the freezing-point as will appear later—is less in quantity in
Bengalis than in Europeans. This is exactly the opposite of what would be
expected.

       Rubner and his pupils have provided very accurate information upon the
relation of climate and the evaporation of water from the lungs and skin (Von
Noorden, Volume 1, page 395). " It is least in temperate climates, it is greater
at low temperatures, and is much increased at high temperatures. The next
most important point is the relative humidity of the atmosphere. Air very
nearly saturated with moisture can take up only a little more water-vapour,
hence the body loses less water in damp than in dry air ". Generally speaking the
quantity of urine varies inversely with the amount of perspiration. The surplus
left by the skin is excreted by the kidneys.

       With regard to the amount of urine passed by the Bengali and its low
specific gravity—the small quantity stands close relationship to the small
amount of total solids it contains and to the almost wholly vegetable character
of the food—poor in nitrogen—upon which they live.

       In the second part of this paper we shall return to this point, when the
results of investigations on urine containing a much higher percentage of solids
will be given.

       3. Urea.—By far the greatest proportion of the nitrogen of metabolism is
excreted by the kidneys in the form of urea. Von Noorden gives the percent-
age as being from 84—87; with animal diet the relative value is higher than
with a mixed or a purely vegetable diet. " Not only the nitrogen of proteid is
excreted in the form of urea, but the proteid decomposition products, glycocoll,
leucin, and tyrosin, also give rise to an increase in urea corresponding to their
contained nitrogen. This is also the case with asparaginic acid and ammonium
salts. The nitrogen of nucleinic acid is also in part at least excreted as urea⁽¹⁾".

       The urea derived from all these different sources that is excreted by
Europeans is generally accepted to be about 30—35 grammes per day or equal
to about a 2 per cent. solution. It is the most important of the nitrogenous
excretions of the body, being the chief end-product of the physiological oxida-
tion of the proteids of the food.

⁽¹⁾ Von Noorder.—The Physiology of Metabolism, 1907.