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884 METABOLISM.
gram of nitrogen does the urine contain. He found the following for 1
gram of nitrogen in the urine: With diet rich in fat 0.747 gram C and 9.22
calories; for carbohydrate-rich diet he found 0.936 gram C and 11.67
calories. The quantity of carbon in the feces can be calculated from the
C
quantity of nitrogen in the feces by using the quotient — = 9.2 (average
with mixed diet, according to Atwater and Benedict.1
)
The extent of the gas exchange can be determined by any of the
methods given on page 869. By multiplying the quantity of carbon dioxide
found by 0.273 one obtains the quantity of carbon eliminated as CO2.
If the total quantity of carbon eliminated in various ways is compared
with the carbon contained in the food, some idea can be obtained as to
the transformation of the carbon compounds. If the quantity of carbon
in the food is greater than in the excreta, then the excess is deposited;
while if the reverse be the case, it shows a corresponding loss of body
substance.
The nature of the substances here deposited or lost, whether they consist
of proteins, fats, or carbohydrates, is learned from the total quantity of the
nitrogen of the excretions. The corresponding quantity of proteins may be cal-
culated from the quantity of nitrogen, and, as the average quantity of carbon
in the proteins is known, the quantity of carbon which corresponds to the decom-
posed proteins may be easily ascertained. If the quantity of carbon thus found
is smaller than the quantity of the total carbon in the excreta, it is then obvious
that some other nitrogen-free substance has been consumed besides the proteins.
If the quantity of carbon in the proteins is considered in round numbers as 52.5
per cent, then the relation between carbon (52.5) and nitrogen (16) is 3.28, or in
round numbers 3.3 : 1. If the total quantity of nitrogen eliminated is multiplied
by 3.3, the excess of carbon in the eliminations over the product found represents
the carbon of the decomposed non-nitrogenous compounds. For instance, in
the case of a person experimented upon, 10 grams of nitrogen and 200 grams of
carbon were eliminated in the course of twenty-four hours; then these 62.5 grams of
protein correspond to 33 grams of carbon, and the difference, 200 — (3.3X10) =167,
represents the quantity of carbon in the decomposed non-nitrogenous compounds.
If we start from the simplest case, starvation, where the body lives at the expense
of its own substance, then, since the quantity of carbohydrates as compared with
the fats of the body is extremely small, in such cases in order to avoid mistakes
the assumption must be made that the person experimented upon has used only
fat and proteins. As animal fat contains on an average 76.5 per cent carbon,
the quantity of transformed fat may be calculated by multiplying the carbon by
~-v = 1.3. In the case of the above example, the person experimented upon
would have used 62.5 grams of proteins and 167X1.3=217 grams of fat, of his
own body, in the course of the twenty-four hours.
Starting from the nitrogen balance, it can be calculated in the same way
whether an excess of carbon in the food as compared with the quantity of carbon
in the excreta is retained by the body as proteins or fat or as both. On the other
hand, with an excess of carbon in the excreta one can determine how much of the
loss of the substance of the body is due to a consumption of the proteins on the
one side and of non-nitrogenous bodies on the other side. How to especially
1
Bull, of Dept. of Agric, U. S., Washington, No. 136.
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