450 PRINCIPLES OF ANIMAL NUTRITION. 
sista | manent 
olizable cued Excess Gain Peromit 
Benes of| Glactne | Food | Cals | Ubfiaa. 
Cais. olism), ; 
Cals. 
Fat...... ea aia eae 1549 944 605 540 89.3 
Carbohydrates............. 1549 944 605 509 84.1 
Meat: 
(| 1549 944 605 418 69.1 
RubNer sci cece gees see 1 1463 944 | 519 332 63.9 
2181 944 1237 805 65.1 
1325 743 582 250 43.0 
Gruber..........++-+-- { 1325 743 582 296 | 50.9 
As was shown in the preceding chapter, however, while the 
recorded determinations of net availability are far from satisfactory 
they show with a considerable degree of probability that there is 
some loss of energy below the maintenance point and that 100 per 
cent. of net availability is at least not ordinarily reached. A lower 
net availabilty, however, means a Jarger maintenance requirement, 
and this in turn results in a larger computed percentage utilization 
of the excess food. 
In the following table the latter percentage has been computed 
by the writer for most of the experiments tabulated on p. 428, as 
well as for those of Rubner and Gruber just cited, on the assump- 
tion that the net availability below the maintenance requirement 
was: 
Meas succicna tae tndar cag odes sal cwee Hee 85 per cent. 
Habs ine swan swanguns esa sgte as 05: fe 8 
Dtatehs ss.ceedwew ened Miso eeeR ess go“ « 
Cane sugar. ... 2... eee eee ee 96“ = « 
The factor for meat is the average of all the results on p. 427; 
that for fat is based on Magnus-Levy’s results upon digestive work; 
those for starch and cane-sugar are the averages of Rubner’s re- 
sults, omitting those which exceed 100 per cent. By dividing the 
fasting metabolism by the above percentages we may compute the 
amount of metabolizable energy required for maintenance on the 
above assumption, while subtracting this from the metabolizable 
energy of the food leaves the amount of excess food, which can be 
compared with the observed gain. 
