136 PRINCIPLES OF ANIMAL NUTRITION. 
final result that the minimum of proteid nitrogen on a diet of pro- 
teids and fat lies between 160 and 200 per cent. of the proteid nitro- 
gen excreted during fasting. These figures when computed on the 
total excretory nitrogen would become 131 per cent. and 163 per 
cent. respectively. 
PROTEIDS AND CARBOHYDRATES.—We have seen (p. 127) that 
the carbohydrates diminish the proteid metabolism to a greater 
extent than the fats. The results which have been reached as to 
their effect in lowering the minimum demand for proteids are on 
the whole in accord with this fact. With a liberal supply of carbo- 
_ hydrates in the food, a much smaller quantity of proteids would 
seem to suffice to maintain nitrogen equilibrium than when the 
non-nitrogenous matter of the ration consists of fat. Indeed, ac- 
cording to some investigators, the proteid metabolism may ever. 
be thus reduced much below that during fasting. 
Munk * appears to have been the first to advance the view last 
mentioned. In an investigation upon the formation of fat from 
carbohydrates a dog was fasted for thirty-one days and then re- 
ceived a diet consisting of a little meat with large amounts of 
carbohydrates (starch and sugar) and also, during the first twelve 
days, gelatin. Omitting these twelve days and also the earlier days 
of the fasting period, the average daily excretion of nitrogen in the 
urine was 
Twelfth to thirty-first days of fasting........... 5.38 grams 
Thirteenth to twenty-fourth days of feeding (200 
grams meat, 500 grams carbohydrates)..... 5.79 “ 
On the seventeenth day of the feeding the urinary nitrogen 
reached the minimum of 4.133 grams, and Munk regards this as 
showing the possibility of a reduction of the proteid metabolism 
considerable below the fasting level. It is to be noted, however, 
that the nitrogen excretion varied considerably from day to day, 
and a selection of a single day for comparison seems hardly justified. 
Hirschfeld ¢ and Kumagawa { found that the nitrogen equili- 
* Arch, path. Anat. u. Physiol., 101, 91. 
} Ibid., 114, 301. 
t Ibid., 116, 370. 
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