IS HUMAN PHYSIOLOGY 



albumens also contain fat and minerals with certain 

 other substances. We thus see that in ordinary 

 modes of feeding we do not take as a rule any food 

 singly or by itself, but in combination with a number 

 of other substances combined with it. It is needful 

 to remark that whilst the distinction between foods 

 which go to build up and repair the bodily substance 

 and those which supply us with energy or working 

 power is a very real one, nevertheless no sharp 

 boundary line can be drawn in practice between the 

 two classes of substances. It is known that under 

 certain circumstances the body-building foods may 

 yield a certain amount of energy, and some 

 physiologists have argued that fat itself may 

 discharge the duties of the tissue-forming items, 

 although this latter view has not received universal 

 support. The probability is that the functions of 

 the two foods are interchangeable in some degree, 

 but that in the ordinary healthy individual their 

 functions are more or less limited to playing the 

 parts just detailed in the nutrition of the body. 



ABOUT WATER. The human body consists by 

 weight of two-thirds of water; and this fact, sur- 

 prising as it may be, does not reveal the whole 

 importance of water as a food. A constant supply 

 of this fluid is required not merely to give to the 

 tissues their proper composition, but a further 

 supply is needed to replace that which is perpetually 

 being used up in the body and excreted by the 

 lungs, skin, and kidneys. Furthermore, water is 

 demanded for the purpose of every vital action, and 

 it is also necessary for the solution of our solid 

 foods so that they may be presented to the digestive 

 organs in a shape which favours their easy assimila- 

 tion. The importance of water as a food is also 



