388 



STOMACH AND INTESTINE. 



always taken into a stomach, or internal ca- 

 vity, part of the total quantity of water which 

 really accompanies them into the system 

 is often introduced by the same mode of 

 absorption. So that, although the amount 

 of water consumed by the organism has pro- 

 bably a definite relation to the activity of the 

 vital processes, the amount of this liquid 

 habitually swallowed by any animal is greatly 

 affected by the quantity introduced in other 

 ways : namely, by the proportion contained 

 in its solid food, the amount formed by the 

 combustion of hydrogen in its body, and 

 the quantity absorbed by its skin from the 

 vaporous or liquid water of the surrounding 

 media. Thus the apparently dry food of many 

 herbivora is explained by the large amount 

 of water, which is present as a chemical con- 

 stituent of such food, and which accompanies 

 its few digestible parts into the system. And 

 the small amount of drink taken by many of 

 the Batrachian reptiles is chiefly due to the 

 active tegumentary ingestion last alluded to. 



The quantity of water contained in the va- 

 rious kinds of food ordinarily made use of, will 

 be referred to hereafter. But we may probably 

 fix its average at about 75 to 80 per cent, 

 (or about 5lbs.) of the mixed fluid and solid 

 food (about 6'5 Ibs.) of the human subject. 



5. The salts of the food constitute the 

 fifth and last group of its constituents, and 

 that of which we may be said to know less 

 than any of the others. For, while many 

 of the more important are easily recognized 

 in the ashes of the various fluid and solid 

 aliments in which they are usually introduced 

 into the body, still we are often at a loss to 

 know the precise state of combination in 

 which they are originally present in the food, 

 far more that in which they enter into com- 

 bination with the organism itself. 



In the case of many salts, we can, indeed, 

 trace the actual changes of composition 

 which occur in the organism. Thus the salts 

 composed of the various organic acids united 

 with the alkalies, are converted into car- 

 bonates, prior to their dismissal from the 

 body in the urine. And it seems possible 

 that even the sulphates ave occasionally 

 decomposed in the alimentary canal ; their 

 sulphuric acid being deoxidized into sul- 

 phuretted hydrogen, while their bases unite 

 with the carbonic acid formed in the system. 

 Hence, although a careful and repeated ana- 

 lysis of the salts contained in the organism 

 and in its total excretions, might afford some 

 clue to the qualities and quantities of the 

 salts which ought to be introduced in the 

 food, it would not by any means represent the 

 details of these demands. While it is hardly 

 necessary to add, that no such series of 

 examinations has ever yet been made ; and 

 that, however carefully conducted, it might 

 easily overlook very small quantities of im- 

 portant ingredients. Many discrepancies, 

 however, it would probably clear up ; such 

 as why animals which in one region seem 

 indifferent to salt, in others seek it with the 

 greatest avidity ; why the diet which pro- 



duces scurvy in one person, leaves another 

 little affected ; and finally, why the roving 

 population of the South American Pampas 

 can maintain a robust health on the fresh 

 meat of the wild cattle which range these 

 plains, while an apparently similar diet on 

 the flesh of tame cattle has been known to 

 destroy English soldiers. 



The more essential salts of the food seem 

 to be the chlorides and phosphates of the 

 alkalies ; and especially, the chloride of so- 

 dium, and the phosphate of soda. Lime and 

 iron are also important bases. All of these 

 ingredients are present in the salts of the milk ; 

 together with some free soda and potash, 

 which are probably combined with its casein. 

 The phosphates are in large quantity ; espe- 

 cially the phosphate of lime the predo- 

 minance of which is doubtless connected with 

 the exigencies of ossification in the foetus. 



Varieties of food. The above grouping 

 of the various constituents of the food, will 

 afford us a valuable clue to the composi- 

 tion of its principal varieties. For however 

 widely these varieties may differ from each 

 other, they always contain representatives 

 from each of the preceding classes. And the 

 best food for any particular animal will always 

 consist of such a proportion of all these con- 

 stituents, as best corresponds to the demands 

 made by the waste of its whole body, and to 

 the peculiarities of its organs of digestion. 



The food most natural to Man is a mixed 

 diet. But though thus far omnivorous, he 

 readily adopts an exclusively animal or vege- 

 table food, according to the circumstances in 

 which he is placed. And there are probably 

 but few of the carnivorous and herbivorous 

 animals, most properly so termed, in whom 

 careful experiments would not detect a simi- 

 lar, though scarcely equal, capacity for such 

 a change of diet. Thus the herbivorous 

 Horse and Cow may be brought to eat fish 

 and flesh ; and the carnivorous sea-birds can 

 be gradually habituated to the far more diffi- 

 cult change implied in their feeding on grain. 

 But many of the frugivorous Quadrumanaseem. 

 little susceptible of such alterations of diet. 

 While there seem to be numerous Insects, 

 which are not only strictly limited to a vege- 

 table food, but even to certain species of 

 plants, or particular parts of their structure. 



The influence of any special variety of food 

 on the human organism depends chiefly on its 

 physical and chemical properties : in other 

 words, on its mechanical arrangement and 

 admixture ; and on the constituents which it 

 presents ; either originally, or as modified by 

 the operations of cooking. Hence these are 

 the chief points which will be noticed in the 

 following short description. 



It is obvious that the division of the 

 various alimentary substances into solid and 

 liquid, or food and drink, is an incorrect one. 

 For, on the one hand, even the driest articles 

 of solid food contain a large proportion of 

 water of composition. And conversely, the 

 purest liquids ordinarily made use of contain 

 a certain quantity of solids, in the shape of 



