344 STUDIES IN LIFE AiYD SENSE. 



other, as adults, we demand several pints of this fluid per day. 

 It enters into the composition of every fluid and tissues of our 

 bodies, and constitutes about 87 per cent, of the bulk of the human 

 frame. Without water we could not dissolve and digest the solids 

 in our foods, nor could the intricate and constant chemical opera- 

 tions including the production of heat of which our bodies are 

 the seat, be carried on without a due supply of this fluid. When 

 one learns that the brain itself including even the ponderous organs 

 of Caudal and his fellow-scientists, which may be presumed to be of 

 the " hardest " description consists at least of between 70 and 80 

 per cent, of water, and that this fluid requires constant replacement, 

 as we shall hereafter see, the importance of water as an article ot 

 diet cannot be over-estimated. Lastly, when one recollects that on 

 water alone, and in the absence of any solid food whatever, human 

 subjects and lower animals have lived on for 50 or 60 days, the 

 necessity of water for animal existence at large is readily seen. 



But our dinner includes, secondly, mineral matter in addition to 

 water ; and we might remark that, in so far as these two items are 

 concerned, mankind presents no superiority of necessities or tastes 

 over the plants. For man, as for the plant, water and minerals 

 appear to be essential for the continuance of existence. For the 

 perfection of our blood, we require to find iron in our food. Lime 

 must be found in the food, that the bones and other tissues may be 

 duly nourished. Phosphoric acid must exist in our nutriment, other- 

 wise the nerve-substance of brain and body will be imperfectly sus- 

 tained. Soda, magnesia, potash, and a host of other minerals are 

 detected in the fluids and structures of the body ; and so intimate 

 and complex are their relations to the composition of our frame, 

 that it appears certain ' that of any two minerals, one cannot replace 

 another, both being necessary for the continuance of health and life. 

 I must not neglect to bear in mind, also, that, like the fungi and 

 other non-green plants, I demand the oxygen of the air as a "respi- 

 ratory food." This gas, which in Smith's well- ventilated dining-room 

 will be supplied to me in perfection, will be inhaled into the lungs, 

 will thence pass into the blood, and there, uniting with carbons 

 derived from fats, starches, and like foods, will produce the heat 

 without which life is an impossibility. Like the plant, then, it is 

 clear we require food of a gaseous kind : the carbonic acid of my fern 

 is replaced in humanity by oxygen. Our food, however, contains 

 certain matters called nitrogenous principles, which, in the truest 

 sense of the term, may be named " flesh-forming " substances. A 

 very considerable part of our bodies consists of " nitrogenous " 

 matters that is, matters which the chemist declares are composed 

 of the four elements, carbon, hydrogen, oxygen, and nitrogen, with 

 traces of sulphur and phosphorus in addition. The importance of 



