330 



CHEMISTRY. 



[MILK, era 



therefore, who take* man water than necessary for nutri- 

 tion and excretion, produces in winter- time, propor- 

 tionately greater quantity of urino ; in summer, aii ex- 

 cessive perspiration. 



$ 67. JIM. A nutriment like milk, which during the 



wbolo period of lif o U of iUclf capable of sustaining the 



formation of blood, is, at it were, a ready answer of 



nature to the question What alimentary principles are 



required for the formation of a complete nutrition t 



:. treating on digestion, we took milk as the prototype 



of a porfoct nutriment. It is at once a solid and a liquid 



| food ; a aouroe of albumen and of fatty substance*, of 



sugar and the salts in one word, it is the most porfoct 



of nutriments. 



While more abundant in water than our blood, more 

 abundant than bread and meat, milk possesses, in caseine, 

 a representative of the albuminous substances, accom- 

 panied by the ready-formed fat of the butter, by a con- 

 stituent of fat in 'the sugar of milk, and by the most 

 important salts of the blood. 



atained in small cellules, which it dilates into 

 glittering globules, the 'fat rises to the surface of the 

 milk which stands undisturbed, forming the cream ; 

 while the lower, and far more abundant part, contains 

 the chief quantity of the casoine, the milk of sugar, and 

 the salts. More than one-third of those salts consists of 

 phosphate of lime, associated with the phosphates of 

 potash and magnesia, with some traces of oxide of iron, 

 chloride of sodium, and a large proportion of chloride of 

 potassium. 



$ 68. QuaKtitt nf Milk. Although the milk of goats 

 and sheep may derive their peculiar smells from the un- 

 combined state of one of the volatile fatty acids, which 

 in the milk of the cow arc united with glycerine into 

 neutral fats, the more important difference between the 

 milk of women and that of animals is exclusively depen- 

 dent ou the different proportion of cascine and sugar of 

 milk, of butter and salts, to be found in these several 

 sort* of milk. Thus, the quantity of casoino in human 

 milk is only half as largo as in that of the cow ; and 

 while, in the latter, butter and salts are likewise con- 

 tained iu greater proportion, human milk exceeds this 

 in the amount of sugar of milk, by more than one-half. 

 However slight the sweetening property of sugar of milk 

 may be, if compared with cane-sugar, the babe does nut 

 fail to distinguish the milk of its mother, from that of 

 the cow, by its sweeter taste. The peculiar butter-fat, 

 or butyrine of the chemist, which, at ordinary tempera- 

 tures, is more fluid than margarine or oleine, must be 

 contained in the human milk in a greater abundance 

 than in that of the cow, as the butter of the latter is of 

 a firmer consistence. 



Immediately after confinement, human milk contains 

 a much greater proportion of solid substances, particularly 

 of butter, than it does some days afterwards. After a 

 striking diminution of these contents of the milk, which 

 has already become remarkable the fourth day after con- 

 finement, the proportionate quantities of casoino and 

 salt* increase again. After weaning, the milk is again 

 impoverished with equal rapidity. 



J69. Formation of Acidi in Milk By the influence 

 of the caseine of the milk, its sugar is transformed into 

 lactic acid, especially at a higher temperature, or in 

 thunder-storms. As oxygen promotes the formation of 

 lactic acid, boiling protects the milk for some time from 

 turning sour the oxygen which is contained in the 

 milk being expelled at the boiling-point. The produc- 

 tion of this acid takes place so much the more easily, 

 inasmuch a* lactic acid is identical with sugar of milk 

 in iu composition. The sour milk becomes thick from 

 the caseino being coagulated by the lactic acid which 

 has been formed ; curdled milk is that in which caseine 

 has been coagulated by the spontaneously transformed 

 lactic acid. If from the curdled milk, the caseine, to 

 which a great part of the butter adheres, be taken away, 

 the whey remains, which is a solution of lactic acid, 

 alts, and sugar, with a much smaller proportion of 

 cawine and butter than U contained in pure milk. 



In batter-milk the proportionate quantity of butter 



especially is diminished ; for it is the remaining part of 

 the cream from which, by the process of churning, tho 

 fats have been tnken off. It always contains, ho" 

 some traces of butter, almost all the sugar of milk, the 

 alto, and the casoino, very little of wliich passes into 

 the butter. 



J 70. Digestibility of Milk. It is natural to suppose 

 that tho food of tho infant must be readily digestible 

 and nutritious ; and both suppositions are verified by 

 experience : for while caseine belongs to tho most soluble 

 of albuminous bodies, the more soluble fats ore repre- 

 sented in tho button Next to cane-sugar, the s 

 of milk is the most readily digestible of all constituents 

 of fat, and its transformation into fat is facilitated by 

 the butter and casciue associated with it. With the 

 easy digestibility of tho milk its nutritivoncss is also 

 proved ; nor need we be astonished at the al'iindaneo of 

 water in an aliment which, at tho same time, furnishes 

 tho infant with solid and liquid food. And if tho weight 

 of the caseine scarcely amounts to one-sixth of that of 

 albuminous bodies in beef, we must not forget that wo 

 commonly take the 4 latter diluted as iu the form of 

 soups, or associated with vegetables or edible roots ; 

 combinations by which the proportionate amount of 

 albumen is considerably diminished. But the quantity 

 of sugar of milk in tho human milk is twice as great as 

 that of caseine, aud the butter is intermediate between 

 both. 



The milk of cows is often assimilated with difficulty 

 by weak digestive organs, from the large proportion of 

 butter it contains ; but skimmed milk is in such cases 

 usually readily digested, and this wo find in a natural 

 state in asses' milk. Poverty in fat, and abundance in 

 sugar, moke asses' milk an invaluable nutriment, main- 

 taining and cheering tho life of many invalids. Several 

 excellent rules are drawn from nature, and none more 

 so than is to be found in the food which nature supplies 

 for tho nourishment of the infant. Wo may consider 

 tho health of the child to be the surest and largest ex- 

 perience which enlightens us as to the right composition 

 of solid and liquid food which man has to partake. This 

 experience confirms the truth, that meat aud bread 

 cannot be taken without water; and that in the best 

 nutriment of mankind, tho albuminous and fatty matters, 

 the constituents of fat, tho compounds of chlorine, and 

 the salts, must be represented without except! 



" Whether food has a yet higher influence," says 

 Forster, in his dissertation on the utility of the bread- 

 fruit tree "whether mind and heart may directly or 

 indirectly be tuned by it, will bo left to our gr. 

 children for discussion. Wo only know that gentle. 

 love, and sensibility of heart, arc tho prominent traits 

 of the people living on bread-fruit." And if we con- 

 sider that, even now, the pastoral tribes are tho gentlest, 

 that the character of the beasts of prey is softened by 

 getting accustomed to a mixed or a vegetable diet, why 

 should it sound fabulous if we connect tho noble tender- 

 ness of heart and pacific meekness of those tribes with 

 the milk and tho fruits upon which they live ?* 



71. Coffee, Tea, and Chocolate. The general opinion 

 that coffee, tea, and chocolate, are beverages which, to 

 a certain degree, may be substituted for each other, is 

 based on a good chemical reason, for all three contain 

 a nitrogenised basis, to which they owe some of i 

 most important chemical properties. Tea and coffee 

 oven contain tho self-same basis, denominated there; 

 indiscriminately, thein or catfein. The basis of choco- 

 late wo will call cocoa-principle. The cocoa-principle, 

 or theobromin, is richer in nitrogen than the thein, 

 which very nearly corresponds in its con with 



flesh-basis. In cold water, them is only with difficulty 

 dissolved, while of cocoa-principle but a small proportion 

 is soluble even in hot water, in wliich tho former readily 

 dissolves. 



While in tea tho basis is combined with common 

 tannio acid, in coffee it forms a salt with a peculiar 

 taunio acid containing a greater proportion of nitrogen, 

 Some curiout renenrchm hare been made in reference to thi by con- 

 linrnul chcmliu; and it luu been mlabliihed u a fact, that diet has an 

 itial connection with moral and mental development. ED 



