Vol,. XVII. No. 4U. 



THE AQRICULTUEAL NEWS. 



69 



the interior are, on the whole, better and stronger workers 

 than those from the town. 



Although the Dominica labourers live mainly on the 

 food of the country, they are remarkably free from deficiency 

 diseases. Pellagra and peripheral neuritis are exceedingly rare 

 in the island; and, most of the few cases I have seen in 

 recent years gave a history showing that the disease was 

 contracted in one of the neighbouring colonies. 



This practical immunity is due to the fact that the food 

 of the people contains abundance of vitamines; although at 

 times and in certain instances it may not contain what until 

 recently has lieen considered the proper proponion of protein. 



THE MEANING OF FOOD VALUES. 



A food may be defined as a substance which, when 

 absorbed by the body, either supplies material to restore 

 tissue-waste, or which supplies energy, or serves both of 

 these functions. 



If a foodstuff is analysed it is found to consist of: — 

 Nitrogenous bodies — proteins, 

 Carbohydrates, 

 Fats, 



Mineral salts. 

 Water. 



Of these, the proteins, mineral salts, and water acting 

 together, can alone restore tissue-waste. 



The proteins also have another valuable property, namely 

 that of producing energy, which properly tbey share with 

 the fats and carbohydrates. In brief, then, the proteins are 

 double foods in th;it they both restore tissue waste and 

 supply energy, while the fats and carbohydrates supply 

 energy alone. It is therefore evident that proteins are 

 indispensable, whilst the other two great group.*, though of 

 great advantage, can on a pinch be done without. 



There are substances in foo'ls which are neither tissue 

 formers nor energy produceis, but which cannot well be 

 dispensed with, namely the mineral salts and indigestible 

 residue. The former are required for the body chemistry, 

 and the latter plays the important part of ballast — that is, 

 a sufficient bulk of material to stimulate intestinal action. 



The term enerjiy, in speaking t f foods, is used in its mechan- 

 ical sense. This energy is converiible into heat in the hody, 

 and by means of it the body can perform work. A simple illus- 

 tration may be given. During its growth, a tree collects its 

 energy from the sun's heat. It is cut down and burnt; in 

 the burning i's energy is reconverted into heat: this hea tmay 

 be used to general.- steam, which can do work in the shape of 

 driving a piston. Instead of a tree let us take a potato; it 

 too collects energy from the sun's heat, it is eaten and burnt 

 up in the body, giving oti" heat which is used to produce the 

 energy neces.sary to ena^ile the body to do work. 



The unit of energy as applied to human food is called 

 the large Ca'orie, and approximately represents the amount 

 of heat necessary to raise l,00ti grams of water 1°C. in 

 temperature. 



It is necessary briefly to mention this point, as all calcula- 

 tions on food value are based on it. 



The energy of the chief constituents of food are: — 



1 gram proteins yields 5 '6 Calories 



1 gram carbohydrates yie ils 4'1 Caloriea 



I gram fats yields 9'4 Calories 



The proteins and carbohydrates are quicker in action 

 than the fat, but have not their staying ^jower. so to speak. 



Taking results that have been obtained from Ihe ukost 

 recent investigations in regard to food energy necessary for 



various degrees of work io a normal adult man of about 1501b, 

 weight, we have the following: — 



At rest, about 2,000 Calories per day. 



Moving about, but no active work, about 2,300 Calories 

 per day. 



Moving about, and light sedentary work, about 2,500 

 Calories per day. 



Moving about, and moderate mechanical work, about 

 3,000 Calories per day. 



Moving about, and active agricultural work, about 

 3,500 Calories per day. 



Moving about, and very active physical work, about 

 4, '(00 Calories per day. 



Moving about, and extremely hard physical work, about 

 5,000 or more Calories per day. 



These results are obtained by figuring a man's day as 

 composed of various activities incident to it, e.g. eight hours 

 sleep, at 65 Calories per hour; two hours for meals, going to 

 and fro, at 170 Calories per hour; six hours sitting, at 100 

 Calories per hour; eight hours of labour, at from 170 to 600 

 Calories per hour, depending upon the degree of activity. 



It may be mentioned thit, according to Dr. Chamber* 

 lain in his book 'Organic Agricultural Chemistry' all efforts 

 to determine the energy expended in even the most sever* 

 mental work have failed. 



Not only, however, does the human body require 

 a certain amount of ener^iy to be supplied in food, but the 

 food must also contain a certain minimum amount of protein. 

 Food protein is essential to the formation of body protein; 

 used np muscle tissue must be replaced by protein supplied 

 in the food. Apart therefore from the energy supplied by 

 the protein in food, a certain amount of protein has to be 

 regarded solely as building or rebuilding material. Thus, 

 although the minimum energy requirement of 2,000 Calories 

 per day for a man might easily be s ipplied by carbohydrates 

 or fats alone, yet, except for a short time, such nonprotein 

 food cannot meet the needs of the body for the replacement 

 of used up tissue. The amount of the protein requirement 

 for an average man of 150 tt). wei>;ht is usually given 

 as 1 00 grams per day, though some investigators reduce it to 

 70 ^rams or even less. 



The figures given above show tha' increased muscular 

 activity raises the energy recjuirement from 2,00(* to 5,000 

 C ilories per day. la contrast to this, the fact is that increased 

 muscular activity has only a slight effect upon the amount of 

 Drotein needed for tissue building. 



Sweet Potato and Yam Quarantine in the 

 United States. — According to a notice rt'ccntly issued 

 by th( ■ United State.s Seci-etary of Agriculture, the iinpor. 

 tation of sweet potatoes and yams (Ipo'im ni batatas and 

 Dloscorca spp.) into the United States from all 

 foreign countries is now forbidden, except for experi- 

 mental or scientific purposes. It is provided, however, 

 that the entry for immediate export, or for immediate 

 transportation and exportation in bond of sweefr 

 potatoes and yams may be permitted. 



This quarantine became effective from January 1 

 IMl.s, and has been establishi'd to prevent the 

 further introduction into the United States of the 

 sweet potato weevils (C?/Zas spp.), and the sweet potato 

 seaialiei' (Kuscepes l^at-atae), which are prevaient* in 

 various parts of the world. 



This notice of quarantine is not to apply to the 

 territories of Hawttii ami Porto Rico. 



