Certain Aspects of Water Metabolism *

It is generally accepted that there exists a definite balance between the intake and output of water so that the water content of the body is maintained within narrow limits at a constant level. Data relative to the distribution of water in the organisms of different species have been collected by Skelton"1. He has shown that the total percentage of water in the body is as follows: man, 63; rat, 65.3; dog, 65.7; cat, 64.2; rabbit, 68.8. It is surprising how little variation is revealed among the different species investigated. Such differences as do occur may perhaps be due to the fact that the various individuals examined were not at the same stage of maturity, for age plays a significant rle in water content of the body. All species exhibit a rapid decrease in water from uterine life to maturity72, when, as predicated by Rubner86, all animals attain the same degree of hydration attended by a loss of the power of growth. Skelton9" has shown that animals of different species distribute their total body weight among the various organs in a similar order and that a given organ tissue has the same percentage water content in the different species. As a rule, the highest percentage of water is found in those tissues concerned in the transportation or excretion of water and in those which possess the greatest functional activity, for exampleheart, blood, lungs, muscles and kidneys. The high specific heat of the water prevents a sudden rise of temperature from the heat produced by the organ's activity. Many factors are concerned in the maintenance of a constant water content in the tissues. Water is furnished not only through food and drink but also through the combustion of foodstuffs. Dependent upon its nature each 100 grams of fuel burned may supply from 50 to 100 grams of water. A greater quantity is released when foodstuffs which have been stored in the organism are used, for when proteins, carbohydrates and fats are stored a cer-