STOMACH AND INTESTINE. 



poorer in all the solid ingredients : and the 

 further continuance of lactation appears chiefly 

 to increase its casein and salts, and diminish 

 its sugar. The copious ingestion of fatty or 

 starchy substances seems to increase the 

 buttery constituent. The over-feeding of a 

 wet-nurse causes her to secrete a milk abnor- 

 mally rich in butter and casein, and injurious 

 to a delicate child. Finally, vigorous exercise 

 appears to diminish both these constituents, 

 especially the former. 



Butter. The composition of the butter 

 contained in milk is as yet but imperfectly 

 known. That of the Cow is stated by 

 Bromeis * to consist of about 68 per cent, of 

 margarine, with 30 of elain, and 2 of fatty 

 matters specific to butter. The exact nature 

 of the latter constituents probably varies in 

 different animals, as well as in different speci- 

 mens of the secretion ; and also seems very 

 liable to be altered by that rancidity which 

 butter so easily acquires from a short expo- 

 sure to the air. Such circumstances quickly 

 give rise to the formation of a variety of vola- 

 tile fatty acids : which are known under the 

 names of butyric, caprylic, capronic, capric, 

 and vaccinic acids. 



The dietetic value of butter can scarcely be 

 rated too highly. It is probably by far the 

 best and most natural form in which hydro- 

 carbons can be supplied to the healthy organ- 

 ism. It is not only attractive to the taste, but 

 is easily assimilated : even by children or 

 adults, whose delicate digestive organs resent 

 the introduction of the ordinary adipose tis- 

 sue of animal food. The quantity which may 

 be advantageously consumed will of course 

 vary with the nature and amount of other 

 food, and with the rate at which combustion 

 proceeds in the body. But the very large 

 amount of this substance habitually consumed 

 by the Hindoos, and by the dairy-men in 

 many of the Alpine highlands of Europe 

 in the latter case often reaching a pound daily 

 is a striking testimony alike of its harm- 

 lessness to the digestive organs, and its value 

 to the system generally. 



Cheese. The substance known by this 

 name consists chiefly of casein ; which has 

 been precipitated from the milk in company 

 with a variable quantity of its buttery con- 

 stituent. Its dietetic value is of course very 

 high. But its digestive properties vary greatly; 

 according to the proportion of fatly matter 

 and salts which it contains, the mechanical 

 aggregation of its mass, and the degree of 

 decomposition which it may have experienced. 



Thus as regards its admixture of butter, 

 we may distinguish three varieties of cheese : 

 one which is made from cream, or from milk 

 with the addition of cream ; one from pure 

 milk ; and one from milk which has been 

 skimmed or deprived of its cream. 



its watery ingredient. This view is corroborated by 

 the fact, that colostrum-corpuscles have been found 

 in the milky contents of the male breast. 



* Annalen ckr Chem. und Pharin. lid. xlii. s. 46. 

 et seq. 



In respect" to its salts, the chief distinction 

 hitherto established appears referrible to the 

 way in which the casein has been precipitated 

 from its solution in the milk. Where the 

 process has been effected by the addition of 

 rennet, the caseous deposit contains a large 

 proportion about 5 or 6 per cent. of 

 phosphate of lime. But where the precipita- 

 tion has been produced by the lactic acid 

 which is gradually developed in milk as the 

 result of its own spontaneous decomposition, 

 the deposit contains scarcely one per cent, of 

 this salt. In such a case, however, the 

 smaller amount of phosphates appears to be 

 partially compensated by the presence of 

 some free phosphoric acid. 



The changes which cheese undergoes by 

 keeping are chiefly manifested in the forma- 

 tion of various volatile fatty acids, that gene- 

 rally communicate their characteristic odour 

 to the whole mass. Such alterations are 

 usually most marked in those varieties of 

 cheese, in which but a small proportion of 

 rennet has been used, and much fatty matter 

 is present. Hence they seem at least par- 

 tially attributable to a metamorphosis pro- 

 bably an oxidation of the buttery con- 

 stituents themselves. In addition to this 

 change, however, the casein also undergoes a 

 somewhat similar fermentation ; which is ac- 

 companied by the production of oxides of 

 casein, and volatile fatty acids. Occasionally 

 the process is carried so far as to constitute 

 a kind of putrefaction, in which the nitrogen 

 originally present is given off in the form of 

 ammonia. The highly poisonous properties 

 which decayed cheese sometimes possesses, 

 and the repulsive odour which it often gives 

 off, may illustrate these statements. 



The value of cheese as an article of food 

 may be to some extent inferred from the 

 large amount of its proteinous constituent, 

 which often forms more than 70 per cent, 

 of its whole weight. This quantity of casein 

 would correspond to about 1 1 J per cent, of 

 nitrogen : a quantity far beyond that contained 

 in any other ordinary variety of azotized food. 

 But just as this unexampled chemical com- 

 position may suffice to indicate how largely 

 such a proportion of the "histogenetic" prin- 

 ciples would require to be diluted with the 

 "respiratory" or "combustible" substances, in 

 order to constitute a food in the true accep- 

 tation of the term, so it partially explains 

 the fact, that cheese is anything but easy of 

 digestion. With many persons even milk is 

 only digested with difficulty ; so that much 

 of its casein may be traced through the 

 bowels, but little changed by the action of the 

 gastric juice. And the mechanical aggregation 

 of many kinds of cheese their extreme hard- 

 ness, dryness, and density, often enable them 

 almost to defy digestion. But minute division, 

 cooking, or careful mastication, will obviate one 

 of these objections ; and the other is easily 

 met by a proper admixture of vegetable food. 

 With such precautions, cheese becomes a 

 most valuable article of food. So that we 

 need be little surprised to find the extreme 



