MKT 



' 7 



om-iderahly in other*. Their work, too, in diller 

 -nt ; iiiul we should expect, ami ex|.crimrni show-, 

 that they require different food. 



Just as (lie life .,1 tin- whole |MH|\ i- the -mil of 

 (heli\e-of the different pait- icelU I ,.f thelMidy. 

 >o the I'IKM! must contain that which is necessary 

 for these parts. The, liody ha> frei|iiently ln-en 

 compared to a steam-engine, hut. a.- \\e ha\e -i\, 



tlie iMxly is complex, and the comparison IOOQM 

 rather be between it and a collection of steam- 

 vngines, each our differing from the other in it-< 

 jtatteru. use, and the kind of fuel required to stoke 

 it. A steam engine requires a store of fuel -<>n 



taiuing the potential-power), by the eoniliusticni of 

 which it moves. It also requite, its part* to be 

 repaired, and sometimes a new loiler or piston is 

 nece-sary. In addition, it requires other tiling, 

 -o that it may work well, such as oil, whicli i- 

 neither burned nor used to build up the machine. 

 In the same way the body, and each part of it, 

 requires first, a store of fuel, from the ooml.u- 

 tion of which its energy or activity is obtained ; 

 secondly, material by \vliioh its wasted parts may 

 be repaired ; and, thirdly, Kiilmtances such as 

 water, salt. \e., which are required by tlie IMK!V, 

 but which are neither burneu nor used entirely 

 in forming tissue. The term ' food ' may then be 

 applied to all that the body requires from without : 

 and following out our comparison, corresponds with 

 the stoking, mending, and oiling of a number of 

 steam-engines. 



Let us consider in the first place the food, which, 

 like the fuel for the engine, the body requires in 

 order to manifest its own peculiar activities. The 

 coal of an engine contains carbon and hydrogen, 

 which become oxidised by the oxygen of the air. 

 As a result of this oxidation, we have heat and 

 mechanical motion. In like manner the body 

 receives food containing large quantities of carbon 

 nd hydrogen. At the same time oxygen is absorbed 

 by the blood as it passes through the lungs. The 

 digested food and the oxygen are taken by the 

 blood to the tissues muscles, brain, &c. and within 

 these tissues a slow oxidation takes place, giving 

 rise to the heat of the body as well as mechanical 

 and other activities. Just as the steam-engine 

 requires a sufficiency of coal, so the body requires a 

 certain quantity of food. In both cases the supply of 

 oxidisable material must have what may be termed 

 A sufficient ' potential ' that is to say, it must 

 have the power of producing a certain amount of 

 heat and mechanical motion. Some coals and some 

 foods burn better than others, and their potential 

 in that case is greater. Fat among the food stalls 

 has the greatest potential, carbohydrates and albu- 

 mens have less. It is obvious then that one cannot 

 speak of the body requiring a certain weight of 

 food per diem. This would mean nothing, for tin- 

 value of different food-stuffs varies considerably, 

 a, pound of one kind of food being equivalent in 

 potential, say, to twenty pounds of another. In 

 Arranging a diet one must carefully consider not 

 only the quantity of food given, hut In addition one 

 must calculate its potential. The steam engine 

 may be driven at full or at half power, and in the 

 latter case the amount of fuel required will K> 

 diminished. In the same way an individual doing 

 hard work requires food with more potential, or, as 

 we say, more nutritious food, than another living an 

 easy and uneventful life, and still more than one 

 confined to the house or to his bed. 



There is yet another important j>oint t<- 1> eon- 

 sidered. In a steam-engine the production of heat 

 is not what is sought as a result of the combustion 

 within the steam-engine; the engineer constructs 

 the machine with a view to obtaining the result of 

 the combustion not in heat, but in mechanical 

 motion. In the best machines, one-tenth of the 



P<.tent ml in converted into work, while the rest, niae- 



tentliM, i* reiect<-< I mi,, the ntiiionpherwa* beat. The 

 human mccliani-m an convert IM much ft* one fifth 

 of the potential of it- f.xwl into work, and < 

 four lift hs into heat. In tlie cae of Ute 

 machine, ho\\e\er, !> neeeeaary. especially 



if the |MH!V In- ill elolh'-d or Mirrouild-.l by (Xtid 



medium. The powerlenMnemi of the hand* when 

 numbed with cold will illu-ti 



a requisite, temperature, \\arm clothing n< ItiaJly 

 saves food. Not onlv is the temperature of the Utdy 

 maintained in a cold climate by j>re\ ruling it 

 duction and radiation from the Imdy by tin- iue of 

 warm clothing, but ap|M-tit- prompt* the conxuinp 

 tion of a large quantity of fod. ami especially llione 

 kinds that contain great potential. The Kkiimw 

 devour great supplies of fat blubber, and they are 

 even said to prefer the taste of rancid oil to that of 

 the less combustible sugar. 



It has been found by experiment that a man 

 of average height and weight, well clothed, in a 

 temperate climate, and doing a fair day'* work, 

 requires such quantity of food that the coml.tuttion 

 of it, were it all converted into mechanical woik. 

 would raise 4000 tons one foot high, or, as it is 

 expressed, 4000 foot-tons. This result has been 

 arrived at by varying the diet until the minimum 

 but sufficient quantity has been arrived at which 

 will preserve the health and vigour. Tin- j 

 tial of the diet can lie calculated by an instru- 

 ment called the calorimeter, which will give the 

 heat produced during the burning of any com- 

 bustible substance, and from the heat produced 

 the potential in respect to mechanical work can 

 be calculated. In the subjoined table the poten- 

 tials of one ounce of each of three important food- 

 stuffs are given : 



FU (beef fat) 1&I-66 



ProteieU (albumen ) l-t 



Carbohydrate* (starch) IM 



It will at once be seen how readily one could cal- 

 culate the amount of food-stuff capaole of furnishing 

 the liody with fuel for twenty-four hour*. All that 

 is necessary will be to divide' 4000 by the number of 

 foot-tons w'hich correspond with the article M-!c-t-d ; 

 the quotient is the number of ounce* required. 

 Thus 1 1 ounces of fat, or 24 ounces of albumen, or 

 26 ounces of starch would contain the necessary 

 potential. 



From what has already been said regarding the 

 complexity of the Unlily mechanism, it may be 

 surmised that a single food stutli even if a quantity 

 lie taken which provides a HUtiicient potential) tt 

 incapable of stoking the Uxly. N u me rous experi- 

 ments, such as those conducted by the (ieUtine 

 Commission, by 1 >r Hammond, and oil 

 cate that the Unly is unable to mainUui 

 natural vigour on* a diet connutting olely of 

 gelatine, or of starch, of albumen, or of fat, fte. 

 Animals fed on a single fo>d -Ht tiff watte rauidly. and 

 will refuse their food after a few days with marked 

 dislike, dying eventually of tarvn- ieant 



t\\o Maple article- of f.iixl taunt be given, mixed. 

 even in this case, with many aoeeeoriei, web. aa 

 various salts, aromatic Kuliotaneea, &c., in order 

 that health may U maintained. 



I.iebig taught that the muix-ulnr work of the body 

 from the oxidation of niimgenom 



i albumen, Uith animal and vegetable), but it i* now 

 known that all the cla*-*-. of i'. M >d .tut!"- oxevijl thf 

 mineral matters are ued by the muncleM. Ne 



thele.-w proteid* (nitrugenou* food) are eiwential. aa 

 we shall see on experimental ground*, and from 

 the fact that in the dietary of even- nation, proteid 

 matter U alwav* prevent, combined at iuiyrat 

 with fat. generally with carbohydrates as welt 

 In many parts of the world man subsists with- 



