A NORMAL DIET 395 



Many investigators have observed and calculated the contributions 

 made by animal and vegetable material to the total food. Particular im- 

 portance has been attached to the content of animal protein, which has 

 been regarded as far superior to vegetable protein. More recent investiga- 

 tion has indicated that this distinction is not altogether justified. It is 

 true that animal proteins are, as a class, rather more effective as builders 

 of body protein than are vegetable proteins but there are marked excep- 

 tions. Thus gelatin is the classic example of an incomplete protein where- 

 as the protein of the potato is one of the most efficient (Hindhede(c) 1913 

 Eose and Cooper) . Isolated plant proteins such as gliadine or zein may bo 

 very inadequate but the mixed proteins of wheat or of maize, as found 

 in flour or meal, will maintain nitrogen equilibrium at a fairly low level, 

 particularly if the whole grain be used or if it be supplemented by a small 

 quantity of other proteins such as those in milk. In any mixed dietary, 

 even if wholly of plant origin, the proteins are almost sure to be suffi- 

 ciently varied to compensate for any individual inadequacies if only 

 the total amount of protein be sufficient. Therefore, no attempt has been 

 made to indicate in Table IV the quantity of animal protein consumed. 

 However, in many cases, that can be calculated from the figures given for 

 protein from meat and from milk and its products. 



But the source of the protein, while of itself of not so great significance, 

 is important as an indication of the amounts of those little known sub- 

 stances, variously denoted food accessories, food hormones, protective sub- 

 stances or vitamines, that may be present. Some idea of the inorganic con- 

 tent of the food may also be obtained in this manner. For this reason, 

 there have been included in Table IV, where the data were available or 

 could readily be calculated, the contributions made to total protein and, in 

 some cases, to total energy also, by each of the classes of food materials, as 

 was done in Table III. The same differences that were evident in Tables 

 II and III also appear in Table IV. In addition, there are differences 

 due to occupation, economic status, etc., most of which have already been 

 discussed. 



In all regions and at all times, man seems to have sought and found 

 some beverage, other than water, to use with his meals. Meat, ale, milk, 

 (sweet and fermented), wine, coffee, tea, cocoa and many others have 

 been used. Particularly striking is the use of four plants of widely dif- 

 ferent botanical nature but all containing caffein or a related substance. 



Changes in Food Habits within Recent Times. The introduction 

 of new foods as a result of the importation of new species, the im- 

 provement of old, or the development of transportation may greatly 

 modify the food habits of a people. Maize and potatoes, unknown 

 before the discovery of America, are to-day two of the staple crops of 

 Europe and are fundamental to the economy f several countries. The 

 improvement of the sugar beet has helped to lower the price of sugar and, 



