386 



STOMACH AND INTESTINE. 



of this material, which the waste of his body 

 probably dismisses from his system within 

 the same period of time. 



2. The next group of alimentary substances 

 is that of the fats, the composition of which 

 has led to their receiving the generic name of 

 hydro- carbons. They are found in both 

 animal and vegetable food. In the milk, they 

 are represented by its butter ; the quantity of 

 which amounts, on an average, to about 3| 

 per cent. 



The great variety of different alimentary 

 substances of this kind is such as to pre- 

 clude even their enumeration. The most 

 important are stearin, elain, and margarin. 

 The composition of these three fats may be 

 generally stated as almost corresponding to 

 single equivalents of carbon and hydrogen: 

 or, more exactly, to ten atoms of each of 

 these elements, minus one of hydrogen, and 

 plus one of oxygen (C 10 H 9 Oj ; or C 7 



The uses sustained by these constitu- 

 ents of the food in the organism are easy 

 to indicate, but difficult to specify. The 

 protection afforded by the fat of the body to 

 its temperature, and to the mechanical safety 

 of its internal structures, might perhaps be ac- 

 complished without involving any rapid waste 

 and replacement of the material by which it 

 is afforded. But the vast quantity of fatty 

 matter which enters into the composition of 

 the nervous system, and the primary import- 

 ance of this delicate and energetic organ to 

 the maintenance of life, entitle us to infer, that 

 its functions imply such a rapid metamorphosis 

 of its substance, as can only be sustained by the 

 continual supply of new materials to replace 

 those rendered effete. And the numerical 

 phenomena of nutrition further show, that 

 the process of respiration is constantly dis- 

 missing from the body an amount of carbonic 

 acid, the proportion of which to the azotized 

 egesta proves that it must have been derived 

 more or less directly from an oxidation of the 

 fatty, as well as of the albuminous, tissues. 

 The quantity of fatty matter contained in the 

 healthy organism strongly confirms these 

 views ; and thus helps to account for its 

 dietetic importance. For, including all their 

 varieties in the tissues just alluded to, we 

 can hardly estimate the total hydro-car- 

 bons of the human body at less than ^th or 

 -^th of its weight. And since they scarcely 

 form e^-cyth part of the blood, it follows, that 

 even assuming this nutrient fluid equal to 

 th of the corporeal weight, its fatty con- 

 stituent amounts to little more than ^ tn or 

 g^oth of the fat which is deposited in the 

 central andperipheric structures of the nervous 

 system, and stored up in the adipose cells 

 of other parts of the body. Such an estimate 

 further entitles us to conjecture, not only that 

 the quantity of fat taken up at any one time 

 by the digestive organs is limited to a very 

 small one ; but also, that it either undergoes 

 some important metamorphosis before reach- 

 ing the general mass of the blood, or is very 

 rapidly eliminated from this fluid. 



3. The hydrates of carbon form a class of 

 nutritional substances, the elementary com- 

 position of which is still more exactly indi- 

 cated by their name. In other words, they 

 consist of carbon, united with hydrogen and 

 oxygen in those equivalent proportions of 

 these two elements which are necessary for 

 the formation of water (C ]2 H 12 O J2 ). This 

 group is a very large one : and includes, not 

 only the various forms of cane, grape, and 

 milk sugar, but a number of kindred sub- 

 stances; such as dextrin, gum, cellulose, 

 inosit, and, especially, starch. All of these 

 organic principles, however various their 

 physical properties, have nevertheless the 

 same chemical composition. And many of 

 them are easily converted into grape sugar; 

 either by the excitement of a limited meta- 

 morphosis by an azotized ferment, or by expo- 

 sure to the action of dilute acids. 



The sugary ingredient of the milk forms 

 about 5^ per cent, of its quantity ; and is the 

 only representative of the hydrates of 

 carbon which it contains. 



The average amount of the substances 

 belonging to this and the preceding group 

 of alimentary constituents will of course 

 vary greatly in the different kinds of food. 

 Speaking generally, however, these two 

 groups may be stated to predominate by 

 turns in the food derived from the two 

 kingdoms of nature. Thus while the hydro- 

 carbons are chiefly derived from the fat of 

 animal food ; the hydrates of carbon belong 

 even more exclusively to the starch and sugar 

 of vegetable food. But, in strictness, no 

 such marked difference can actually be made 

 out between the two kinds of food in this re- 

 spect. The milk, the liver, and even the blood of 

 the animal, all contain sugar : while inosit, a 

 substance closely allied to sugar, forms an im- 

 portant constituent of its various muscles. And 

 not only do many plants contain large quan- 

 tities of oily matter stored up in various parts 

 of their tissues, but even the seeds of the ce- 

 realia, which form the best vegetable diet, 

 present an amount of fat ranging from '2 to 

 2 per cent. 



The purposes fulfilled by these hydrates of 

 carbon in the animal economy, offer a marked 

 contrast to those subserved by the two pre- 

 vious groups. The protein compounds form 

 what is eminently the basis of the organism ; 

 the plasma from which are developed the 

 blood and the tissues. They are thus his- 

 togenetic and hcemagenetic, as the phrase is. 

 The fatty matters of the body not only form 

 a large constituent of the active nervous sub- 

 stance, but are also retained and stored up 

 in the more inert and passive form of adi- 

 pose tissue. While the grape-sugar, into 

 which the various hydrates of carbon are all 

 finally converted, appears never to assume 

 any permanent form in the body, but to be 

 always rapidly eliminated from the blood. In 

 what shape, or after what metamorphoses, it 

 leaves this fluid, is at present uncertain. It 

 is, however, probable, that like the hydro- 

 carbons, these hydrates of carbon are essen- 



