662 STARCH AND SUGAR. [BOOK 11. 



this is true not only of the inorganic salines such as chlorides 

 and phosphates but also of the so-called extractives. As we 

 have seen, the presence of these bodies, both the simpler inor- 

 ganic and the more complex organic salts, in the blood or in the 

 extra vascular juices or lymph of the tissues is essential to or 

 directs or modifies the metabolic activity of the several tissues. 

 The beneficial effects, as components of special diets, of such 

 things as beef-tea and meat-extract, which consist chiefly of 

 salts and extractives with a very small quantity of albumose or 

 other forms of proteid, and the effects either beneficial or dele- 

 terious of drugs both turn in common upon their taking a part 

 of some kind or other in, it may be upon their interference with 

 metabolic processes. The salts and extractives of a diet may 

 be looked upon as necessary daily medicines, and a medicine as 

 a more or less extraordinary variation in these elements of a 

 diet. 



Alcohol, to the use of which as a component of an ordinary 

 diet special interest for various reasons attaches, comes in this 

 class. For though observations shew that the greater part of 

 a moderate dose of alcohol is oxidized within the body and so 

 serves as a source of energy, man has recourse to alcohol not 

 for the minute quantity of energy which is supplied by itself, 

 but for its powerful influence on the distribution of the energy 

 furnished by other things. That influence is a very complex 

 one and cannot be fully discussed here. We may add that the 

 physiological action of alcoholic drinks is still further compli- 

 cated by the fact that most such drinks contain besides ethylic 

 alcohol, various other allied substances, whose action is even 

 more potent than that of the ethylic alcohol itself, and whose 

 presence very markedly determines the total effect of the drink. 

 Such articles of diet as tea and coffee stand upon very much 

 the same footing as alcohol. 



The quantity of fluid which a man drinks or should drink 

 daily, or more correctly the quantity of water which he should 

 daily add to the dry solids of his diet, must vary widely accord- 

 ing to circumstance. It will differ according as he is perspir- 

 ing greatly or not, according to the nature of the dry solids 

 of the diet, whether largely carbohydrate or not, and so on. 

 A lower limit, below which excretion is impeded, and a higher 

 limit, above which digestion and metabolism are injuriously 

 affected, probably exist; but we have as yet no adequate data 

 which will enable us to fix either of them. 



442. In the selection of articles of food to supply the 

 food-stuffs and other constituents of a normal diet, regard 

 must of course be had in the first place to the amount of poten- 

 tial energy present in the material. The articles chosen for 

 the daily fare must contain between them so much proteid, fat, 

 arid carbohydrate representing so much available energy. But 



