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TEXT-BOOK OF PHYSIOLOGY. 



The daily excretion of carbon, therefore, indicates the extent of fat metab- 

 olism. The carbohydrates are here left out of consideration, as they con- 

 stitute 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 fat that the protein would give rise to, as previously deter- 

 mined, must therefore be subtracted from that eliminated by the lungs, etc., 

 in order to determine the amount of body-fat metabolized. Observations 

 of human beings in the fasting condition show that for a period of ten days 

 there is a daily excretion of about 24 grams of urea, equivalent to about 72 

 grams of protein. This amount, however, may be reduced to from 40 to 50 

 per cent, if the individual has a surplus of body-fat. Human beings under 

 similar circumstances may lose during the first few days from 180 to 200 

 grams of fat. 



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, in all probability, from 

 a cessation in the action of the heart. 



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. 



The results of an analysis of the organs and tissues of a cat after a thirteen- 

 day period of starvation, during which the animal lost 1017 grams in weight, 

 are given in the following table, based on data furnished by Voit: 



It will be observed from this table that the adipose tissue suffers the 

 greatest loss, the entire amount disappearing with the exception of a small 

 portion in the posterior part of the orbital cavity and around the kidneys. 

 The muscles, though losing only 31 per cent, of their weight, yet furnish 

 429 grams of presumably protein material, for nutritive purposes. The 

 heart and nervous system experience but slight loss. 



