812 EXPERIMENT STATION RECORD. 



require about 2,200 kg. of hay and 750 kg. of straw. Therefore this 

 amount of material must be procured and so preserved that its mois- 

 ture content will not be changed during the experiment. Three to 5 

 per cent of the material (66 to 110 kg. of hay and 22 to 38 kg. of straw) 

 should be taken for sampling. The hay or straw should be spread out 

 in an even layer on paper or suitable material and portions taken here 

 and there. These portions should in the same way be mixed and 

 spread in an even layer and from the mixture final samples taken for 

 analysis. 



In experiments with cows it is necessary to determine the nitrogen 

 in the fresh feces, since nitrogen is lost if the material is dried. The 

 Kjeldahl method is used for this purpose. The fat may be determined 

 in the usual way, using ether distilled over sodium. The crude fiber 

 should be determined by heating the substance in autoclaves at 3 

 atmospheres pressure in glycerin-sulphuric acid (20 gm. sulphuric acid 

 to 1 liter glycerin). 



An elementary analysis may be combined with determination of the 

 heat of combustion of different materials by collecting the resulting 

 gas in the bomb, measuring it, and analyzing small portions. 



BALANCE OF INCOME AND OUTGO. 



In accurate metabolism experiments, in addition to the determina- 

 tions noted above, it is necessary to measure the carbon dioxid excreted 

 in the breath. It is also desirable to measure the oxygen consumed 

 from the air, although fairly accurate results may be obtained when 

 only the carbon dioxid is measured, as is done with the Pettenkofer 

 respiration apparatus. 



When protein, fat, and carbohydrates are the only materials utilized 

 in the animal body, as is the case with Carnivora, determining the 

 outgo of carbon in addition to the nitrogen in the urine is sufficient. 

 Thus, in an experiment with a dog the urine was found to contain 17 

 gm. of nitrogen and 14.3 gm. carbon and the respired air 160 gm. car- 

 bon per day on a diet of protein and fat in one instance and of fat and 

 starch in another. As protein contains 16 per cent of nitrogen and 53 

 per cent of carbon — i. e., in the proportion of 16 to 53 — the 17 gm. of 

 nitrogen would call for 56.3 gm. carbon. Of this, 14.3 gm. was found 

 in the urine, leaving 42 gm. of carbon to be ascribed to the protein 

 broken down in the body. Since 160 gm. carbon was excreted in the 

 respired air, 118 gm. (160—42) must have been derived from starch or 

 fat. Animal fat is fairly uniform in composition, containing in round 

 numbers 77 per cent carbon, 12 per cent hydrogen, and 11 per cent 

 oxygen, while starch contains 44.4 per cent carbon, 6.2 per cent hydro- 

 gen, and 49.4 per cent oxygen; that is, 153 gm. fat or 266 gm. starch 

 would furnish 118 gm. carbon. 



