"The combination of two foods equal in calories is represented by a point midway between them. Thus, to combine one' portion' of bread and one' portion' of butter (Fig. 9) draw a straight line between their points and at the middle of it mark a cross and label it ' 2'; this point will represent two ' portions' of bread and butter.
"If the calories of the two foods are unequal, the point representing the combination will be proportionately nearer the point with the-larger number. Thus, if one portion of bread is combined with one-half portion of butter, the bread and butter point will be midway between the points for bread and for butter, but will lie twice as near the bread point as the butter point.
"When three foods are combined, the point representing the combination is, in like manner, the 'center of gravity' of the three, and may be found by first obtaining the center of gravity of two, and then obtaining the center of gravity of the point thus obtained, and the third. Thus if, as in Fig. 10, we have three points representing respectively, 3, 4 and 5 calories of three separate foods, shown by the attached numbers 3, 4 and 5, the point representing the combination may be found by joining the points labeled 3 and 4, and finding their center of gravity 7, situated nearer the point 4 than point 3, and dividing the line between them in the ratio of 3 to 4. The first two points, 3 and 4, may be considered as concentrated at 7 with their combined weight, 7. We then find the center of gravity of this new point 7 and the remaining point, 5. The center of gravity at this point 7 and point 5 will be a point 12, on the straight line between them, situated nearer the 7 than the 5, and dividing the distance between in the ratio of 5 to 7. At point 12 the whole combination of 12 portions may be considered to be concentrated. It is evident that we could find the center of gravity of the same three points by combining them in a different order, but the result would be the same.
Fig. 9. Food Map Showing Combination of one "Por-tion" of Bread and one "Portion" of Butter.
Fig. 10. Showing Method of Combining Three or More Foods.
"It is evident that more than three points may be combined on the same principles by combining them by twos and threes and then combining the combinations. * * * *
"If we accept Professor Chittenden's results as to proteid requirements, a well balanced daily ration for the average person will be represented by a point lying within the' normal rectangle,' as shown in Fig. 11. This shows that proteid should be near 10 per cent. * * * *
"Since the resultant point, representing the ration, is the center of gravity of the points representing its constituents, it is evident it can be obtained by mechanical as well as by geometrical methods. For this purpose a mechanical diet indicator has been devised, as shown in Fig. 12.
Fig 11. Food Map with "Normal Rectangle." Chittenden's Standard, of Well Balanced Ration.
"The essential feature of this apparatus is a card on which is drawn the right-angled triangle with which we have already become familiar. Points on this card may be located to represent the various foods employed. These points may be easilv found from table given at the end of this article. . . .
At points representing foods eaten, pins with heavy heads are thrust through the cardboard, the weight of each representing one 'standard portion.' Similar pins but one-half and one-quarter as heavy are also provided to represent half and quarter 'portions.' When these pins are placed the total ration which has been consumed is easily found, simply by counting the ' portions' thus represented. In order to find the precentages of proteid, fat and carbohydrate in this rations it is only necessary to obtain the center of gravity of all the pins. For this purpose the card is placed in a basket and suspended on a standard so that the center of gravity is easily indicated on the card by means of a vertical pricker, which may be pressed on the card. Thus, almost instantaneously, the center of gravity is found. The total time consumed in placing the pins, adjusting the card and basket, and finding the center of gravity, is found to be, for accurate work, about five minutes".
Fig. 12. Mechanical Diet Indicator.
Professor Fisher's mechanical diet indicator is now manufactured and may be obtained through the Purchasing Department of this School for $25.00, express collect.
Further details are given in the original article, reprint of which will be loaned to Members of the School for lc. postage.
Aside from the "food map" and the diet indicator, the table will repay careful study in making clear the real composition of foods as eaten.
The proportion of proteids given in the table for some of the foods is not absolutely correct, as proteid-like substances like gelatin and also the so-called "extractives," the latter having no food value, are calculated as proteids. The error is not serious, for the proportion of such substances is usually very small.
The table is particularly valuable in showing equivalent total food values. After weighing out a few "portions" of various foods it is very easy to tell by the eye the amount of food being served and so obtain a fairly accurate idea of the total food value of one's diet. An ordinary postal scale will serve for weighing.