CHAPTER XI 



ANIMALS THAT LIVE WITHOUT 

 WATER 



In water-conserving ability, man compares poorly with 

 many other animals, some of which can subsist with no 

 source of water other than the moisture of their food 

 (preformed water) and that generated by the oxida- 

 tion of this food in the body— so-called metabohc water/ 

 We have briefly mentioned metabolic water in connec- 

 tion with the lungfish, reptiles and birds, but did not 

 enlarge on the topic because of lack of information on its 

 importance to these forms. In the present connection, 

 however, the term warrants detailed definition. Each 

 of the three foodstuffs, carbohydrate, fat, and protein, 

 contains a high proportion of hydrogen to carbon; as 

 oxidation converts the carbon to carbon dioxide, the 

 hydrogen is oxidized to water: one hundred grams of 

 dry starch on oxidation yield 55.6 cc, one hundred 

 grams of fat yield on the average 107 cc, one hundred 

 grams of protein, if the nitrogen is degraded to ammonia, 

 urea, or uric acid, yield, respectively, 32, 39.6 and 53 cc. 

 of water. On a balanced diet (3000 calories) of 465 

 grams of carbohydrate, 85 grams of fat and 90 grams of 

 protein, the metabolic water in man would amount to 

 335 cc. per day. But under the most favorable conditions 

 man loses 700 cc. of water per day through his skin and 

 lungs; hence, taking the minimal urine flow on a mixed 

 diet as 900 cc, his minimal additional water requirement 



