QUANTITY OF FOOD REQUIRED. 39 



From the experiments of Boussingault with reference to fat, and of 

 Bidder and Schmidt with reference to the albuminates, and Maximum lim- 

 of Yon Becker with reference to the carbohydrates, we learn J^SStS 

 that only definite quantities of these substances can be ab- mentsoffood. 

 sorbed by the intestine in definite periods of time. This maximum limit 

 is, however, far more than the necessities of the system require ; hence in 

 overfeeding, though much of the excess of food passes away with the ex- 

 crement, a very large portion is, as it were, needlessly absorbed, and, un- 

 dergoing metamorphosis in the blood, is removed by the kidneys. To 

 this portion Lehmann applies the designation introduced by Schmidt, 

 luxus consumption, or superfluous consumption. Of course, the simplest 

 condition under which we can investigate the normal quantity of food 

 required is that of an invariable weight, and the difficulties of the inquiry 

 are increased when growth, corpulence, pregnancy, or other such states, 

 are included. 



Though we are very far from being able to offer a complete solution 

 of the problem of the amount of food required, in its most general sense, 

 yet, through the labors of many chemists, we have accumulated several 

 facts which have a bearing on this question. Thus it is known that albu- 

 minous substances alone can not be absorbed in quantity enough to com- 

 pensate for the loss of carbon by respiration. A duck, as is shown by 

 Boussingault, expires in one hour 1.25 grammes of carbon, but can only 

 absorb of carbon in albuminates 1. 00 gramme. So, in like manner, fat alone 

 is inadequate, for of this substance 0.84 gramme, containing about 0.70 

 gramme of carbon, can only be taken up in an hour, and this is not much 

 more than half of what the respiratory operation demands. The carbo- 

 hydrates, however, can be absorbed in sufficient proportion, and in this 

 mixed manner are all the requirements satisfied. Boussingault makes 

 the curious remark that, in the quantity of starch, 5.26 parts, and the 

 quantity of sugar, 5.62 parts, which this bird can absorb in one hour, 

 there are nearly the same quantities, 2.37, of carbon. 



Among the special investigations which have been made to determine 

 the amount of food used and the amount of educts from the Amount of 

 system, should be mentioned that of Valentin upon himself, food, and 

 His weight was 117 Ibs. ; his diurnal consumption of food, 

 6.451 Ibs.; solid excrement, .42 lb.; urine, 4.686 Ibs.; and 2.751 Ibs. 

 perspiration. From the more recent and very exact experiments of Bar- 

 ral, it is inferred that of 100 grammes of carbon which have been ab- 

 sorbed into the organism, 91.59 escape as carbonic acid through the lungs 

 and skin, 4.58 appear, in the urine, and 3.83 are re-excreted and appear 

 in the fasces. Upon similar principles, Lehmann computes, from the 

 data furnished by Barral, that for every 100 parts of absorbed nitrogen, 

 49.6 parts are removed through the skin and lungs, 42.07 are found in 



