34 OF MIXED DIETS. 



which presents many analogies to casein, is coagulable by acetic acid 

 and alcohol, and, if mixed with sugar, turns curdy, and becomes sour 

 from the presence of lactic acid. It differs from casein in not dissolving 

 in concentrated acetic acid, and, when precipitated by an acid, being un- 

 acted on by carbonate of lime. It is, however, coagulated by rennet. 



Thus, when we use bread made of any of the common varieties of flour, 

 we find in it both kinds of food, the respiratory and nutritive the former 

 as starch, and the latter as fibrin. 



But civilized man has greatly improved on the simple diet which Na- 

 Use of butter ture furnishes, and, without knowing the immediate or philo- 

 on bread. sophical reason, has added articles which increase the respira- 

 tory element. The proverb says, "It is good to have bread, but it is 

 better to have bread and butter." Let us examine why it is so. 



Wheaten flour, in its relations to the animal system, is defective in one 

 point its respiratory element, the starch. Now the constitution of starch 

 is, that in its dry state it contains much more than half its weight of wa- 

 ter, none of its hydrogen being free, but all oxidized. It is, therefore, 

 only by the use of very considerable quantities of bread that the neces- 

 sary amount of respiratory food can be had for keeping up the tempera- 

 ture to the proper degree. But if butter be put upon the bread, the effect 

 is different. In common with all oleaginous bodies, butter contains an 

 excess of hydrogen, and therefore, under the same weight, possesses a 

 very high heating power. The defect of the flour is thus compensated, 

 and by the use of quite a moderate quantity a high temperature can be 

 maintained. 



It would be very interesting to examine in this way the physiological 

 relations of the diets adopted by communities of men, and the great 

 changes which, at quite a recent period, have taken place through the in- 

 troduction of tea, coffee, and chocolate on an extensive scale among civ- 

 ilized nations. Before the discovery of the passage to the East by the 

 Cape of Good Hope, and the establishment of direct commercial relations 

 between Western Europe and China, the general diet of the agricultural 

 classes consisted chiefly of the common products of the farm and sub- 

 Of mixed di- stances readily obtained in domestic economy, such as bread, 

 cheese 8 and^' an( l*cheese, and beer. In a theoretical point of view, we can 

 beer. scarcely conceive of a diet more conducive to the sustenance 



of the bodily frame. The constitution of wheat flour shows that it con- 

 tains the elements necessary for life ; and cheese, which may be regarded 

 as the preserved curd of milk, is an excellent flesh-producing body, the 

 casein of which it consists being readily convertible into muscle-fibrin. 

 The common salt used in its preparation promotes the function of diges- 

 tion, by furnishing hydrochloric acid and soda. In addition, there are 

 also in the beer, an alcoholic and intoxicating liquid, all the advantages 



