CHAMBERS'S INFORMATION FOR THE PEOPLE. 



a goose-quill, into the duodenum. The chyme, 

 when mixed with these fluids, undergoes a change 

 in its appearance : it assumes a yellow colour and 

 bitter taste, owing to the predominance of the 

 bile in the mass ; but its character varies accord- 

 ing to the nature of the food that has been taken. 

 Fatty matters, tendons, cartilages, white of eggs, 

 &c. are not so readily converted into chyme as 

 fibrous or fleshy, cheesy, and gelatinous substances. 

 The chyme, having undergone the changes ad- 

 verted to, is urged by the peristaltic motion of the 

 intestines onwards through the alimentary canal. 

 This curious motion of the intestines is caused by 

 the contraction of the muscular coat which enters 

 into their structure, and one of the principal uses 

 ascribed to the bile is that of stimulating them to 

 this motion. If the peristaltic motion be dimin- 

 ished, owing to a deficiency of bile, then the 

 progress of digestion is retarded, and the intes- 

 tines become constipated. In such cases, calomel, 

 the blue pill, and other medicines, are admin- 

 istered, for the purpose of stimulating the liver to 

 secrete the biliary fluid, that it may quicken, by 

 its stimulating properties, the peristaltic action. 



The preceding, however, is not the only use 

 of the bile ; it also assists in separating the nu- 

 tritious from the non-nutritious portion of the 

 alimentary mass, for the chyme now presents 

 a mixture of a fluid termed chyle, which is in 

 reality the nutritious portion eliminated from the 

 food. The chyme thus mixed with chyle arrives 

 in the small intestines, on the walls of which a 

 series of exquisitely delicate vessels ramify in 

 every direction. These vessels absorb or take up 

 the chyle, leaving the rest of the mass to be 

 ejected from the body. The chyle, thus taken up, 

 is carried into little bodies or glands, where it 

 is still further elaborated, acquiring additional 

 nutritious properties ; after which corresponding 

 vessels, emerging from these glands, carry along 

 the fluid to a comparatively large vessel, called 

 the thoracic duct, which ascends in the abdomen 

 along the side of the backbone, and pours it into 

 that side of the heart to which the blood that 

 has already circulated through the body returns. 

 Here the chyle is intimately mixed with the 

 blood, which fluid is now propelled into the lungs, 

 Avhere it undergoes, from being exposed to the 

 action of the air we breathe, the changes necessary 

 to render it again fit for circulation. It is in the 

 lungs, therefore, that the process of digestion is 

 completed : the blood has now acquired those 

 nutritive properties from which it secretes the new 

 particles of matter adapted to supply the waste of 

 the different textures of the body. 



When food is received into the stomach, the 

 secretion of the gastric juice immediately com- 

 mences ; and when a full meal has been taken, 

 this secretion generally lasts for about an hour. 

 It is a law of vital action, that when any living 

 organ is called into play, there is immediately an 

 increased flow of blood and nervous energy towards 

 it. The stomach, while secreting the gastric juice, 

 displays this phenomenon, and the consequence is 

 that the blood and nervous energy are called away 

 from other organs. This is the cause of that 

 chilliness at the extremities which we often feel 

 after eating . heartily. So great is the demand 

 which the stomach thus makes upon the rest of 

 the system, that during and for some time after a 

 meal we are not in a condition to take strong 



721 



exercise of any kind. Both body and mind are 

 inactive and languid. They are so simply because 

 that which supports muscular and mental activity 

 is concentrated for the time upon the organs of 

 digestion. This is an arrangement of nature 

 which a regard to health requires that we should 

 not interfere with. We should indulge in the 

 muscular and mental repose which is demanded j 

 and this should last for not much less than an 

 hotir after every regular meal. In that time the 

 secretion of gastric juice is nearly finished, and 

 we are again fit for active exertion. The conse- 

 quence of not observing this rule is often very 

 hurtful. Strong exercise, or mental application, 

 during or immediately after a meal, diverts the 

 flow of nervous energy and of blood to the stomach, 

 and the process of digestion is necessarily retarded 

 or stopped. Confusion and obstruction are thus 

 introduced into the system, and a tendency to the 

 terrible calamity of dyspepsy is perhaps estab- 

 lished. 



For the same reason that repose is required 

 after a meal, it is necessary in some measure for 

 a little while before. At the moment when we 

 have concluded a severe muscular task such, for 

 example, as a long walk the flow of nervous 

 energy and of circulation is strongly directed to 

 the muscular system. It requires some time to 

 allow this flow to stop and subside ; and till this 

 takes place, it is not proper to bring the stomach 

 into exercise, as the demand which it makes when 

 filled would not in that case be answered. In like 

 manner also, if we be engaged in close mental 

 application, the nervous energy and circulation 

 being in that case directed to the brain, it is not 

 right all at once to call another and distant organ 

 into play ; some time is required to allow of the 

 energy and circulation being prepared to take the 

 new direction. It may therefore be laid down as 

 a maxim, that a short period of repose, or at least 

 of very light occupation, should be allowed before 

 every meal. 



It is remarkable that these rules, although the 

 natural reasons for them were not perhaps well 

 known, 'have long been followed with regard to 

 animals upon which man sets a value, while as yet 

 their application to the human constitution is 

 thought of only by a few. Those intrusted with 

 horses and dogs will not allow them to feed 

 immediately after exercise ; nor will they allow 

 them to be subjected to exercise for some time 

 after feeding. Experience has also instructed 

 veteran soldiers not to dine the instant that a long 

 march has been concluded, but to wait coolly till 

 ample time has been allowed for all the proper 

 preparations. 



Although strong mental and muscular exercise 

 shoald be avoided before, during, and immediately 

 after a meal, there can be no objection to the light 

 and lively chat which is generally indulged in 

 where several are met to eat together. On the 

 contrary, it is believed that jocund conversation is 

 useful towards the process of nutrition. 



Kinds of Food. 



It has been shewn, by a reference to the struc 

 ture of the human intestinal canal, that our food 

 designed to be a mixture of animal and vegetable 

 substances. There is, it is to be remarked, a 

 power of adaptation in nature, by which inc 

 viduals may be enabled for a considerable time 



