FOODS 



129 



6.25 parts of protein. Hence, for every i gram of nitrogen or 2.14 grams 

 urea excreted, it may be assumed that 6.25 grams of protein or, according 

 to Voit, 30 grams of flesh have been metabolized. The daily excretion of 

 urea, after the first five days therefore, indicates fairly accurately the extent 

 of the metabolism of the tissue protein. 



It has been observed also that there is a steady diminution in the excre- 

 tion of carbon dioxid. As fat contains about 76 per cent, of carbon, i part 

 of carbon equals 3.66 parts of carbon dioxid or 1.31 parts of fat. Hence, 

 for every i gram of carbon or 3.66 grams carbon dioxid excreted it may be 

 assumed that 1.31 grams of fat have been metabolized. The daily excre- 

 tion of carbon, therefore, indicates the extent of fat metabolism. The car- 

 bohydrates are here left out of consideration, as they constitute only about 

 i per cent, of the body-weight. It must be borne in mind, however, that 

 in the metabolism of protein a certain quantity of fat or sugar is produced, 

 which also undergoes oxidation. The amount of the carbon or the CO 2 that 

 the protein would give rise to, as previously determined, must therefore be 

 subtracted from that eliminated by the lungs, etc., in order to determine the 

 amount of body-fat metabolized. 



In a fasting experiment, voluntarily undergone by a human being, and 

 lasting ten days, the metabolism of fat as shown by the CO 2 excreted 

 amounted to 136.7 grams during the first four days and to 132 grams on 

 the tenth day. In another similar experiment lasting five days, the fat 

 metabolized amounted to 206 grams on the first day and 181 grams on the 

 fifth day. As the starvation period lengthens the amount of fat metabo- 

 lized gradually declines. 



The following table shows the excretion of nitrogen and carbon and 

 the calculated amounts of protein and fat metabolized from an experiment 

 made by Ranke on himself during a fast of twenty hours, beginning twenty- 

 four hours after the last meal : 



Coincidently with these losses to the body there is also a gradual loss of 

 inorganic salts, and toward the termination of the period a sudden fall in 

 temperature of several degrees centigrade, in consequence of the final con- 

 sumption of all available foods, when death ensues. The immediate cause 

 of death is not, however, apparent. 



Post-mortem Appearances. It has been experimentally determined that 

 animals die when the body-weight has declined to about 40 per cent. Post- 

 mortem examination shows that the loss of material, though very generally 

 distributed throughout the body, is greatest in organs and tissues least 

 essential to life. 



