Thus, after food which is rich in such vegetables as potatoes, or after fruit with much fruit acids, the urine can become less acid; but after food that abounds in proteids the urine becomes acid. This happens after eating much meat, or leguminous vegetables rich in proteids. Such a very acid urine is often passed by diabetics; therefore in their diet a certain amount of fruits, rich in salts but poor in sugar, may give good results. The most rational diet is that which combines all the principal items of nourishment—in the greatest proportion proteids, as from such the body is built up and waste tissues replaced; next in proportion carbohydrates, from which, as already shown, we obtain muscular energy; and to a smaller extent than the two preceding must be taken fat, which serves to produce heat in the body. Besides these three important constituents there is a further class of valuable substances indispensable for our well-being, and these are the mineral matters. From experiments made by Lunin[267] in Bunge’s laboratory, and by Förster,[268] it has been shown that animals cannot live if fed on food that is devoid of mineral matters; and the latter savant has further shown that animals can live longer without any food at all than with food that has no salt whatever. We need these salts for different purposes, such as building up the skeleton; and the condition of the teeth depends also on the richness of our bodies in lime, and in order to obtain this it is indispensable to introduce food that contains a maximum of it. This is of special importance in the nutrition of children. Footnote 267: Lunin: Diss Dorpat, 1880. Zeitschrift für Physiolog. Chemie, vol. v. March 1, 1881; quoted after Bunge. Footnote 268: Förster: Zeitschrift für Biologie, vol. ix, p. 247, 1873; quoted after Bunge. We give below a table by Bunge showing the amount of lime contained in many of our common articles of diet; 100 grammes of dried substance yields milligrammes of lime:— Cows’ milk 1510 Human milk 243 Strawberries 483 Figs 400 Yolk of eggs 380 Prunes 160 Peas 137 Dates 108 White of egg 130 Potatoes 100 Pears 95 Malaga 60 grapes Graham bread 77 But beef, 24 only