Dec. 19, 1884.] 



♦ KNOWLEDGE ♦ 



495 



AN ILUISI RATED 



" MAGAZINE OF SCIENCE ^ 



Plainlyy/orded-exactlyDescribed^ 



LONDON: FRIDAY, DEC. 19. 1884. 



Contents op No. 164. 



PAGB 



The Chemistry of CooTtery. XLIX. 



By W. Mattieu Williams 495 



Chats on Geometrical Measurement : 



The Conic Sections. {Illtia.) By 



R. A. Proctor 496 



Tho Entomolo^ of a Pond. UUm.) 



ByE. A. Butler 497 



PoUtical Life in America. By R. A. 



Proctor 490 



A Marvellous Little Stream 499 



Earth's Shape and Motions. (i?/««.) 



By R. A. Proctor 500 



Electroplating: Preparing the Bath, 



&c. By W. SliDgo 503 



Pi.GH 



Automatic Arctic Exploration 5i 3 



Zodiacal Mapa. By R. A. Proctor 504 

 A Sheep Destroyer. {Hint.) By 



John R. Coryell 504 



Chapters on Modem Dome&tic 



Economv 5C6 



The Tricycle in 18S4. By John 



Browning 507 



Reviews: Custom and Myth 608 



Face of the Sty. By F.R.A.S 510 



Miscellanea 511 



Correspondence 511 



Our Inventors' Column 513 



Out Chess Column 514 



THE CHEMISTRY OF COOKERY. 



By "W. Mattieu Williams. 

 XLIX.— THE MODEEN THEORY OF FOOD. 



IN my last I summarised Liebig's theory of the source of 

 vital power, and its supposed refutation by modern 

 experiments, but had not space to state the substituted 

 theory. I will now endeavour to do so, though not without 

 difficulty, nor with iatisfactory result, seeing that the 

 recent theorists are vague and self-contradictory. All 

 agree that vital power or liberated force is obtained at the 

 expense of some kind of chemical action of a destructive or 

 oxidising character, and is, therefore, theoretically analogous 

 to the source of power in a steam-engine ; but when they 

 come to the practical question of the demand for working 

 fuel or food, they abandon this analogy. 



Pavy says (Treatise on Food and Dietetics, page 6) : — " In 

 the liberation of actual force, a complete analogy may le 

 traced between the animal sjstem and a steam-engine. 

 Both are media for the conversion cf latent into actual 

 force. In the animal system, combustible material is 

 supplied under the form of the various kinds of food, 

 and oxygen is taken in for the process of respiration. 

 From the chemical energy due to the combination of these, 

 force is liberated in an active state; and besides manifesting 

 itself as heat, and in other ways peculiar to the animal 

 system, is capable of performing mechanical work." In 

 another place (page 59 of same work), after describing 

 Liebig's view, Dr. Pavy says, " The facts which have been 

 already adduced (ihose described in my last paper) suthce 

 to refute this doctrine. Indeed, it may be considered as 

 abundantly proved that food does not require to become 

 organised tissue before it can be rendered available for 

 force-production." On page 81 he says : — " While nitro- 

 genous matter may be regarded as forming the essential 

 basis of structures possessing active or living properties, 

 tJte non-nitrogenous principles may he looked upon as sup- 

 plying the source of power. The one may be spoken of as 

 holding the position of the instrument of action, while the 

 other supplies the motive power. Nitrogenous alimentary 

 matter may, it is true, by oxidation, contribute to the gene- 

 ration cf the moving force, but, as has been explained, in 



fulfilling this office there is evidence before us to show that 

 it is split up into two distinct poriions, one containing the 

 nitrogen ichich is eliminated as useless, and a residuary non- 

 nitrogenous portion which is retained and utilised in force- 

 production" 



The italics are mine, for reasons presently to be ex- 

 plained. The following pages of Pavy's work contain 

 repetitions and illustrations of this attribution of the 

 origin of force to the non-nitrogenous elements of food. 



Then we have a statement of the experiments of Joule 

 on the mechanical equivalent of heat, connected with 

 experiments of Frankland with the apparatus that is used 

 for determining the calorific value of coal, kc. — viz , a little 

 tubular furnace charged with a mixture of the combustible 

 to be tested, and chlorate of potash (better a mixture of 

 chlorate and nitrate). This being placed iu a tube, open 

 below, and thrust under water, is fired, and gives out all its 

 heat to the surrounding liquid, the rise cf temperature of 

 which measures the calorific value of the substance. 



From this result is calculated the mechanical work 

 obtainable from a given quantity of different food mate- 

 rials. That from a gramme is given as follows : — 



Beef fat 27,778 •) Units of wort. 



Starch (arrowroot) 11,983^ or number of 



Lamp SBgar 10,254 1 pounds lifted 



Grape sugar 10,038^ one foot. 



In Dr. Edward Smith's treatise on " Food," the foot 

 pound equivalent of each kind of food is specifically stated 

 in such a manner as to lead the student to conclude that 

 this represents its actual working efficiency as food. 

 Other modern writers represent it in like manner. 



Here, then, comes the bearing of these theories on my 

 subject. A practical dietary or menu is demanded, say, for 

 navvies or for athletes in full work ; another for sedentary 

 people doing little work of any kind. 



According to the new theory, the best possible food for 

 the first class is fat, butter being superior to lean beef in 

 the proportion of U,421 to 2,820 (Smith), beef fat 

 having nearly eight times the value of lean beef. Ten 

 grains of rice gives 7,45-l: foot pounds of working power, 

 while the same quantity of lean beef only 2,829 ; accord- 

 ing to which 1 lb. of rice should supply as mnch support to 

 hard workers as 2^ lb. of beef-steak. None of the modern 

 theorists dare to be consistent when dealing with such 

 direct practical applications. 



I might quote a multitude of other palpable incon- 

 sistences cf the theory, which is so slippery that it 

 cannot be firmly grasped. Thus, Dr. Pavy (page 403), 

 immediately after describing bacon fat as " the most effi- 

 cient kind of force-producing material," and stating that 

 "the non nitrogenous alimentary principles appear to 

 possess a higher dietetic value than the nitrogenous,^' tells 

 us that "the performance of work may be looked upon as 

 necessitating a proportionate supply of nitrogenous alimen- 

 tary matter," and his reason for this admission being that 

 such nitrogenous material is required for the nutrition of 

 the muscles themselves. 



A pretty tissue of inconsistences is thus supplied ! 

 Non-nitrogenous food is the best force-prcducer — it corre- 

 sponds to the fuel of the steam-engine ; the nitrogenous is 

 necessary only to repair the machine. Nevertheless, when 

 force-production is specially demanded, the food required is 

 not the force-producer, but the special builder of muscles, 

 the which muscles are not used up and renewed in doing 

 the work. 



It must be remembered that the whole of this modern 

 theoretical fabric is built upon the experiments which are 

 supposed to show that there is no more elimination of 

 nitrogenous matter during hard work than during rest. 



