Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/228

210 210 DIETETICS tributed to physiology a precision rarely attainable in our dealings with social economy. Mr Joule of Manchester analyzed, about thirty years ago, the relation which the heat, used as a source of power in machinery, bore to the force of motion thus made active. He showed that raising the temperature of 1 fi) of water 1 Fahr. was equivalent to raising 772 fi to the height of 1 foot ; and conversely, that the fall of 772 Ib might be so applied as to heat 1 fi) of water 1 Fahr. Thus, the mechanical work represented in lifting 772 K&amp;gt; 1 foot, or 1 K&amp;gt; 772 feet, forms the &quot; dynamic equivalent,&quot; the measure of the possible strength of 1 of temperature as marked by the thermometer in 1 fi) of water. Physiologists seized eagerly on the opportunity which Joule s demonstration seemed to afford them of estimating in actual numerals the relation of living bodies to the work they have to do. So much earth raised on an embankment represents so much heat developed in the machinery, be it living or dead. The fully digested food, converted through several stages into gaseous, liquid, and solid excretory matters, produces by its chemical changes a definite amount of heat, of which a definite amount escapes and a definite amount is employed in working the involuntary machinery of the body, and the rest is available for conversion at will into voluntary muscular actions. It may be reckoned that the daily expenditure of force in working the machinery of the body in raising the diaphragm about 15 times and contracting the heart about 60 times a minute, in continuously rolling the wave of the intestinal canal, and in various other involuntary move ments, without anything to be fairly called work, it may be reckoned that the expenditure of force in doing this is equal to that which would raise a man of 10 stone 10,000 feet. There are several reasons for believing that in assigning their physiological functions to the several sorts of food, nearly all the business of begetting force should be ascribed to the solid hydrocarbons, starch and oil, by their conver sion into carbonic acid and water, just as there are good grounds for thinking that it is the conversion of the solid hydrocarbon of coal into the same substances which drives a locomotive. To the nitrogenous aliments seems allotted primarily the task of continuously replacing the wear and tear of the nitrogenous tissues, while any excess of them assists the starch and oil in keeping up the animal heat. One of the most cogent of the reasons for this view is that the chief nitrogenous excretion, the urea, is not in creased in amount in proportion to the work done, as shown by the experiments of Messrs Fink and Wiscelenus ; whereas the excretion of carbonic acid in a decided manner follows the amount of muscular exertion. Now, it is very clear that if the supply of power to do work depended on the decomposition and renewal of the muscles by flesh food, the urea must be exactly proportioned to the exertion, which is not the case. To give an example of the mode of working out a problem by this theory. Professor Frankland, in a series of experiments made in 18G.6 at the Royal Institution, and published in the London Philosophical Magazine, vol. xxxii. p. 182, ascertains with the &quot; calorimeter &quot; (which reckons the amount of heat evolved as a thermometer does its degree) the quantity of energy or force evolved under the form of heat during the oxidation of a given weight of alimentary substance. It has been explained that heat and mechani cal work, being convertible into one another, bear a constant proportion to one another ; so that a delinite pro duction of so much heat invariably represents the poten tiality of so much motion, used or wasted according to circumstances. From the reading of the calorimeter there fore may be calculated how many extra pounds ought to be raised a foot high by a man who has eaten an extra pound of the food in question ; how many steps a foot high he ought to raise a weight of ten stone (say himself) before he has worked out the value of his victuals. Pro fessor Fraukland has thus estimated the comparative value of foods as bases of muscular exertion, and he has made out a table of the weight and cost of various articles that would require to be consumed daily to enable a man to support life, the equivalent of which has been already reckoned as the muscular force in action which would raise a man of 10 stone 10,000 feet. Name of Food. Weight in jioiuids requii-L d. Price per Lb. Cost, Cheshire cheese rise s. d. 10 s. d. Hi Potatoes 5-068 1 Apples. . . 7-315 H n 3 Oatmeal 1-981 2* 4 1 Flour 1 311 9.3 33 Peameal 1-335 3 1 4 1 Ground rice 1-341 4 51 Arrowroot 1&quot;&amp;gt;87 1 1 &amp;lt;M Bread 2 345 2 44 Lean beef. 3 532 1 3 61 Lean veal 4-300 1 4 3 Lean ham (boiled) Mackerel 3-001 3-124 1 6 8 4 6 9 i Whiting... . 6 369 1 4 Q A White of egg 8-745 6 4 4 1 Hard-boiled eg&quot; 2 209 6^ i 91 Isinglass 1-377 16 99 fii Milk 8 021 o 24 1 S&quot; Carrots 9 685 1* 1 i Cabbage 12 020 1 1 0* Cocoa-nibs 0-735 1 6 1 l- 1 - Butter 693 1 6 1 O 1 Beef fat... 555 10 r )i Cod-liver oil 0-553 3 6 ] 111 Lump su 7 ar .... 1 505 6 9 Commercial grape sugar Bass s pale ale (bottled) Guinness s stout 1-537 9 bottles. 6 s bottles 3i 10&quot; 10 o f4 7 6 K. 71 &amp;gt; 1$ After the supply of sufficient albuminoid matters in the food to provide for the necessary renewal of the tissues, the best materials for the production of internal and external work are non -nitrogenous matters, such as oil, fat, sugar, starch, gum, &c. When the work is increased, not so much extra meat as vegetable food, or its dietetic equivalent, fat, is demanded. In comparing the cost of a daily sufficiency of the various foods to produce the required force, we must not forget the inconveniences which many of them entail. These incon veniences must be added to the cost. For example, suppose a man to have been living upon potatoes only, just supporting life with 5 fi&amp;gt; a day, and then to get work which enabled him and required him to take a double supply of non-nitrogenous food, he would act unwisely if he were to swallow it in the form of 12 Bb of cabbage. He would be knocked up by the shear labour of carrying 1 2 fi) extra in a vessel so ill-adapted to sustain heavy loads as the stomach. A similar objection would lie against milk, or veal, or apples, however cheap accident might make them ; and a more serious objection still would hold against nine bottles of ale, or seven of stout. On the other hand, the over-concentration of cheese, beef dripping, and lump sugar, makes them nauseous when in large quantity or monotonously persisted in, though when introduced as a variety they are appetizing and digestible. There is no saving in using that against which the stomach is set, or which the absorbents refuse to assimilate. Reverting to the illustration of the gang of a hundred prisoners, and supposing it were requisite to put them on hard labour equivalent to half &quot; Frankland s unit &quot; of 10
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