624 LECTURE XXVII. 



protein in the egesta with that in the ingesta, we can tell whether all of 

 the carbon has been eliminated or whether more or less. In the two latter 

 cases we can tell whether the organism has consumed its own protein or 

 fat, or whether it has added to its supply of albumin and of nitrogen-free 

 substances. 



We have disregarded the losses which the body sustains by its secretions, 

 and the losses of epidermis from the skin, intestinal canal, and other mucous 

 membranes. These losses are very hard to estimate. To some extent they 

 come into consideration with the eliminations from the alimentary canal 

 in the analysis of the faeces. They may be disregarded, or not be estimated 

 by themselves, because they are so small in amount that the error intro- 

 duced does not assert itself in the nutrition balance. Particular attention 

 should be paid to the nitrogen content of the faeces, which arises largely 

 from intestinal depositions. The faeces of man contain 0.5 to 1.4 grams of 

 nitrogen, even when the food contains but little nitrogen or none. Among 

 the nitrogen-free products, the faeces contain principally fat. In starvation 

 man eliminates 0.6 to 1.4 grams of fat per day. With nourishment free 

 from fat, 3 to 7 grams are eliminated daily. 



For the determination of the heat given off by the organism, a special 

 apparatus is also necessary. A calorimeter which permits the simultaneous 

 determination of the respiratory exchange and the amount of heat liberated 

 is Atwater's respiration calorimeter. 1 This apparatus, in which the person, 

 or animal, experimented upon may remain for a week, consists of a chamber 

 which is large enough to be comfortable. This space is supplied with a 

 ventilating arrangement, so that the volume of the air can be accurately 

 measured. It is so regulated that the air enters and leaves at exactly the 

 same temperature. Now and then samples of air are taken as it enters and 

 as it leaves the chamber, whereby the amount of carbon dioxide and water 

 given off by the lungs and by the skin is determined. Suitable arrange- 

 ments are also provided for the introduction of food and drink, and for 

 the removal of the solid and liquid excretory products. The amount of 

 heat given up by the organism, together with the heat equivalent 

 of the external muscular work, is measured at the same time. The heat 

 given off is carried away by a stream of cold water, which flows in tubes 

 around the chamber. By carefully regulating the temperature of the water 

 and the velocity at which it flows through -the tubes, it is possible to carry 

 away the heat as fast as it is produced, thereby keeping the temperature 

 of the chamber constant. By determining the amount of water that has 

 flowed through the tube, and the change in temperature, it is possible to 

 estimate the amount of heat given off by the body. 



By determining the amount of water vapor in the air as it enters and as it 

 leaves the chamber, it is possible to find out how much water is given off by 



1 Loc. dt. p. 499. 



