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                    In the Presidency Jail, Calcutta, Midnapore Jail and Puri Jail
               we estimated the total nitrogen of both urine and fæces. In the
               remaining jail we decided to rely on the total nitrogen of the urine
               for our results. Our reasons for so doing were that we found a
               good deal of difficulty in separating the fæces corresponding to the
               diet given, owing to the fluid character of the stools. It was
               also very difficult to deal with the large volume of fæces passed
               by the prisoners, and the unpleasant nature of the work was a
               serious source of objection to its being properly performed.

     Our main reason, however, for giving up the fæces estimations and relying on
the urine—thus following Chittenden's method—was that we found that, so long as
the prisoners were healthy and taking their food properly, very similar results
were obtained whether we worked with the fæces or the urine.

     In order to make allowance for the nitrogen that had undergone metabolism
in the body but was eliminated by the skin, or in the stools in the remains of the
digestive juices and intestinal débris, we decided to add 0.5 gramme of nitrogen
per man daily to the total nitrogen of the urine. This may be a little too low,
but it does not affect the results to any appreciable extent.

     As indicated above, we had to eliminate all source of error by examining only
prisoners in good health and at once rejecting anyone who showed signs of
sickness. On several occasions we have rejected a whole batch and the work done
on it for this reason.

     Another factor that we had to take into consideration was the gain or loss
in body-weight. Although it is practically certain that, in a very large proportion
of cases, a temporary gain in body-weight is not accompanied by a retention of
nitrogen, but is due to retention of water or storing of fat, still we decided to reject
all observations—in which the urine was relied on—when anything more than a
trifling difference in the average weight of the batch existed between the first and
last day of observation. As a matter of fact while there was, in every instance, a
gain in weight as soon as the prisoners were placed on a weighed-out dietary, after
the first few days the average weight of a batch remained practically constant.

     In this connection the very large bulk of the stools passed and their average
weight was a very marked feature; furthermore, it was noticed how very similar
the percentage of nitrogen present in the mixed fæces of a batch was from day to
day whatever the weight the stools happened to be, or whatever the diet given.
This has been observed by other workers* and, without pressing the point, it was
found that the percentage of nitrogen of the fæces was fairly uniform under
different conditions, while the amount of total nitrogen varied largely with the
total weight of the stools passed.

* Prausnitz, Zeitsch f. Biologie. 1897.

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