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to say in his paper on this subject,“ there are few dead into chyle, the food is first intimately mixed with the Digestion. bodies in which the stomach at its great end is not in general secretions of the stomach, and after it has been Digestian some degree digested."
acted on by them, the solvent liquor is poured upon it, 165 but the
That the chyle is not formed there, and that it is by which the nutritious part is dissolved. This solution chvle form- commonly formed before the food passes through the py- is afterwards conveyed into the pyloric portion, where ed in the lorus, is proved by the result of soine experiments made it is mixed with the secretions peculiar to that cavity, pyloric por. by Mr Hunter upon dogs, in the year 1760. The dogs and converted into chyle.
were killed while digestion was going on; and in all, “ The great strength of the muscles of the pyloric
“ In animals whose food is easy of digestion, the sto. Solvent li. From the result of these experiments, as well as from mach consists of a cardiac and pyloric portion only; but quor se.
the analogy of other animals, it is reasonable to believe, in those whose food is difficult ef digestion, other parts creted by that the glands situated at the termination of the cuticu are superadded, in which it undergoes a preparation beglands near
lar lining of the æsophagus, which are described by Mr fore it is submitted to that process.” the gullet.
Home, secrete the solvent liquor, which is occasionally The action of the juices of the stomach, or of what Action a poured on the food, so as to be intimately mixed with it we call the gastric juice, appears to have much more ef- the gastrie before it is removed from the cardiac portion ; and the fect in the process of chymification, than the muscular
juice. 167 muscular contraction retains it there, till this takes place. action of the stomach, though the dissolving power of Curvature Such contraction being occasionally required in the this fluid seems to be proportionally less in those aniof the sto- stomach, accounts for its being more or less bent upon mals that have the most muscular stomachs. The gacounted for itself, as by this structure it is more readily divided into stric juice of granivorous birds is capable of dissolving
two portions, by the action of the muscular fibres at that "flesh; but when this is entire, it requires four or fire part where the angle is formed.
days for solution ; whereas when bruised, half that time This contraction also explains why the contents of is sufficient. Even grain is not dissolved in it except the stomach are not completely discharged from the first when bruised. The gastric juice of animals with intereffect of an emetic; and by it Mr Home thinks we may niediate stomachs dissolves flesh and cartilage, but not
explain the cramp of the stomach, and some kinds of in bone. It is incapable of dissolving entire seeds. In 168 digestion.
animals with membranous stomachs, the gastric juice is Ornitho After comparing the stomachs of several carnivorous extremely active, and seems to be almost the only agent *- rinchus the animals with that of man; in tracing the gradation from : in the digestive process. In some of these animals
, real link
carnivorous beasts through the bat tribe to birds of prey, however, as the ruminating tribes, this fluid has no efbetween quadrupeds
Mr Home remarks, that “the only real link between fect on the food, unless it be bruised, or thoroughly and birds. the stomachs of quadrupeds and birds is that of the or- masticated. Spallanzani found, that owls digest Hesh
nithorinchus (or platypus), which, lowever, is more an and bones, but not grain ;--that the gastric juice of the approach to the gizzard, heing lined with a cuticle con eagle dissolves bread and bone, and even animal and taining sand, and baving the same relative situation to vegetable matters, when it is taken out of the body;the æsophagus and duodenum. The food of this animal "that a wood pigeon may be gradually brought to live is not known; it is probably of both kinds; the papillæ on flesh ;-that the owl and falcon do not digest bread;
at the pylorus; which appear to be the secretory ducts-that the gastric juice of the dog dissolves even the 169 of glands, are peculiar to it.
enamel of the teeth. General From the facts and observations brought forward in Hence, in every order of animals, the gastric juice is conclusions, this valuable paper, Mr Home deduces the following the principal cause of digestion, and it agrees in all in
general conclusions. * “ That the solvent liquor is se- many properties, and differs in others. In the frog, the i creted from glands of a somewhat similar structure in newt, scaly fishes, and other cold-blooded animals, it pro
all animals, but much larger and more conspicuous in duces digestion in a temperature nearly equal to that of some than in others.
the atmosphere. In warm-blooded animals it is capable “ That these glands are always situated near the ori- of dissolving the aliment in a degree of heat lower than fice of the cavity, the contents of which are exposed to that of these animals. In them too the food is digested their secretion.
in a few hours, whereas in the opposite kind it requires “That the viscid substance found on the internal several days, and even weeks, particularly in serpents ; membrane of all the stomacbs that were examined re likewise, the gastric juice of the gallinaceous class can cently after death, is reduced to this state by a secre dissolve only bodies of a soft and yielding texture, and tion from the whole surface of the stomach, which coa previously triturated: whilst in others, as serpents, the gulates albumen. This appears to be proved, by every heron, birds of prev, and the dog, it decomposes subpart of the fourth cavity of tbe calf's stomach having stances of great tenacity, as ligaments and tendons ; the property of coagulating milk.
and even of considerable hardness, as the most compact “ This property in the general secretion of the sto bone. Man belongs to this class, but his gastric juice mach leads to an opinion, that the coagulation of fluid seems to have no action on the hardest kinds of bones. substances is necessary for their being acted on by the Some species, likewise, are incapable of digesting vegesolvent liquor; and a practical observation of the late tables, as birds of prey; but man, the dog, cat, crows, Mr Hunter, that weak stomachs can digest only solid &c. dissolve the individuals of both kingdoms alike, and food, is in confirmation of it.
are omnivorous, and in general their gastric juices pro" That in converting animal and vegetable substances duce these effects out of the body.
For an account of the chemical nature and properties nous and spirituous liquors and old cheese in small quanDigestion. of the gastric juice, see CHEMISTRY, No 2551. tities, and by various bitters. It is retarded by large Digestion.
The process of chymification depends also, in a great quantities of diluting liquors, especially when taken
measure, on the nature of the substances employed as hot; by acids and astringents taken a short time after Solubility
food, as some of these are much more soluble than eatings by unctuous substances; by mental employ
others. On this subject much information may be de- ment, or severe bodily exercise, too soon after a meal; * Stark's rived by consulting the experiments of Dr Stark *, and and by leaning with the breast against a table.
172 Works, those of M. Gosse of Geneva, an abstract of which is It may be proper here to notice the various opinions Various
theories of given in Johnson's Animal Chemistry, vol. i. p. 207. that have been entertained respecting the immediate
digestion. From the latter experiments it appears, Ist, That the fol cause of digestion. The principal of these opinions are, lowing substances are either insoluble, or are not digest that it is produced by coction or beat; by trituration ed in the usual time in the stomach. in the stomach; by fermentation, or by putrefaction.
173 Animal substances. 1. Tendinous parts. 2. Bones. That it is not brought about by heat alone, will ap- Heat. 3. Oily or fatty parts. 4. Indurated white of egg. pear from the circumstance, that many cold blooded
Vegetable substances. 1. Oily or emulsive seeds. animals digest their food as completely, though not so Expressed oils of different nuts and kernels. 3. Dried expeditiously, as warm-blooded animals. grapes. 4. Rind of farinaceous substances. 5. Pods of That it is not effected by trituration in the stomach Trituration. beans and pease. 6. Skins of stone fruits. 7. Husks of alone, is evident from the experiments that have been fruit, with grains or seeds. 8. Capsules of fruit, with made by Spallanzani, Stevens, and others, of giving to grains. 9. Ligneous stones of fruits. 10. The gastric animals food enclosed in hollow perforated balls, sutfjuice does not destroy the life of some seeds; hence bit- ciently strong to resist the muscular power of the stoter-sweet, hemp, misletoe, and other plants which some mach; us the balls have been found empty, and not times grow upon trees, are produced by the means of compressed. the excrements of birds, the kernels of seeds being de That it is not owing to fermentation is proved by the Fermentafended from the menstruam by their exterior covering. circumstance, that the more perfectly digestion proceeds,
2d, That the following are partly soluble, viz. the less is the evolution of gases in the stomach; the
Animal substances. 1. Pork dressed various ways. 2. contrary of which would be the case, if digestion con-
That it does not depend on putridity, is evidenced by Putridity. Vegetable Substances.--1. Salads of different kinds, the observations that have been made on putrid food rendered more so when dressed. 2. White of cabbage given to dogs, and examined some time alter, when it less soluble than red. 3. Beet, cardoons, onions, and was found perfectly sweet. leeks. 4. Root of scurvy-grass, red and yellow carrots, On the whole it appears, that in most animals the disuccory, are more insoluble in the form of salad than gestion of food in the stomach depends partly on a due any other way. 5. Pulp of fruit with acids, when not degree of heat, partly on the vital action of the stomach, fluid. 6. Warm bread and sweet pastry, from their pro but chiefly on the action of the gastric juice. ducing acidity. 7. Fresh and dry figs. By frying all When the aliments have been converted in the sto- Chylifica.
tion. these substances in butter or oil they become still less mach to the crude pulp called chyme, they are gradually soluble. If they are not dissolved in the stomach, they propelled through the pylorus into the duodenum, where are, however, in the course of their passage through the they are mixed with the bile, the pancreatic juice, and intestines.
the fluids that are separated by the mucous coat of that 3d, That the following are soluble, or easy of dige- intestine, and are thus reduced to a still finer pulp, constion, being generally reduced to chyme in an hour, or taining, as one of its principal ingredients, the nutritious an hour and a half.
flaid called chyle, the nature and properties of wbich, Animal Substances.-1. Veal, lamb, and in general as they have been but slightly mentioned in the former the flesh of young animals, are sooner dissolved than that parts of this work, fall to be noticed bere.
Properties of old. 3. Cows milk. 4. Perch boil. The properties of chyle bave not been minutely in
of chyle. ed with a little salt and parsley. . When fried or sea vestigated; but according to Fordyce, as far as experisoned with oil, wine, and white sauce, it is not so ment has been carried, the chyle of quadrupeds is so soluble.
similar to that of man, and of each other, as hardly to
4. Pulp or meal of farinaceous seeds. The chyle consists of three parts; one part which is
whole white and opake. These globules have been sup-
2. Fresh eggs.
Of been made very probable. The difficulty of determin- ringing in the ears, confusion or depravation of sight, of Digestion ing these points arises from the small quantity that can &c.; and if the former symptoms arise to a great height, Digestions
be collested, the largest animals not supplying more than as in the case of overloaded stomach or surfeit, coma,
agulating on extravasation; the part agreeing with se nervous affections, particularly hysteria and bypochon* Fordyce rum in its qualities; the globular part, wbich in some driasis, in which there frequently takes place astonishing on Dige animals, but not in quadrupeds, exists without giving accumulations of air in the stomach and bowels, the stian.
whiteness to the chyle-alone, or along with sugar, form affections of the head, such as stupor, confusion of 179 Progress of the essential parts of the chyle *
thought, partial blindness, &c. sometimes proceed to the chyle. The compound pulpy matter containing the chyle is such a height, as to threaten, or even sometimes to pro
carried forward from the duodenum through the whole duce, an apoplectic paroxysm. In many cases these affeccourse of the intestines, where it is subjected to the con tions are referred immediately to the head; but are protinual action of the internal wrinkled membrane of the ved, in most instances, to depend on the disordered state bowels, and its nutritious particles, or chyle, selected of the alimentary canal, from the immediate relief proand absorbed by the lacteals that are abundantly distri cured by those remedies which promote the discharge of
buted there, and open their mouths directly within the air, or produce copious evacuation from the bowels. On 130
the other hand, in some diseases, where the head is priPassage
As to the movements of the alimentary canal, the marily affected, as in phrenitis hydrocephalica (water in af food through the
direction of hairs found in the stomach, and the balls the head), the complaint is referred to the bowels, from intestines, of hairs which are thrown "p, would appear to indicate the costiveness or other disordered state of these. The
a circular motion. The intestinal part has a motion daily experience of literary men shows how much intense
small parcels into his mouth, and restore them separately
182 before they enter into the pores of their bodies, and The relations between the digestive and the locomo- Relations that many of them abound in acrid juices, which are tive functions, are not less obvious. Experience shews between well fitted for this solution. It does not appear that how much digestion depends on regular exercise, and digestion
plants possess what may be called the faculty of di how imperfectly it is carried on in the stomach of the and motion. 191 gestion.
indolent and sedentary ; while on the other hand, when Relations The relations between digestion and the functions we the stomach is overloaded, voluntary motion becomes between di; have already considered, especially sensation, are various difficult and fatiguing. Spasmodic contractions of the gestion and sensation.
and important. The sympathies that exist between the muscles, twitchings of the limbs, and similar affections,
(6) That ruminating power which is natural to the quadrupeds of the order Pecora, is sometimes met with in
We have heard of persons who regularly brought up their food into the mouth soon after eating, chewed it over again, swallowed the juices with the saliva, and spat out the more solid parts. In these cases, the rumination
heartburn, water-brash or pyrosis, loss of appetite, and Mr John Hunter made several experiments to shew Of Absorption. inordinate appetite; for an account of wbich, see the that the veins do not absorb. He conveyed milk, co- Absorption. article MEDICINE. loured with various dyeing substances, or perfumed with
187 musk, into the small intestines of an ass, which was soon CHAP VI. Of Absorption.
after killed. On opening the veins of the intestines, and veins. 184
allowing the blood to separate into serum and crassaAbsorption. We have said that the chyle is taken up from the
mentum, the serum was found neither to be tinged with compound pulpy matter composed of the food and the
the colouring matters, nor scented by the perfume, while animal juices, as it passes through the intestines, by the the coloured milk was evident in the lacteals. That the lacteals. This, however, is not the only absorption that veins, however, do in some cases perform the office of takes place in the animal body. The fluids poured out absorbents, is evident from the speedy depletion of the into cavities by the exhalant arteries, as well as all the
corpora cavernosa penis, after having been distended secreted or exuding fluids, and even the solid materials of with arterious blood; and from a similar depletion that the system, are taken up by the lymphatics, and carried takes place iu the nipple of the female breast.
188 into the circulation; the blood poured out into cells in The principal object in dispute respecting the function By tbe some parts, is evidently absorbed by veins; and, as we of absorption in man and the higher classes of animals, skin,
shall endeavour to prove, an absorption takes place over is, whether the skin possesses the power of absorption. 185 the external surface of the body.
This question, as it is both curious and important, we
the superior animals, of the lact als, the mesenteric pose we shall avail ourselves of an able paper on the
Leçons, tom. iv. leç. xxiii. and Blumenbach's Compara- this doctrine of inhalation has been called in question,
and, in the opinion of many, entirely overthrown. It By lacteals The action of the lacteals and lymphatics is probably has been said, that this absorption neither does nor can and lym much the same, and is exerted in a similar manner. take place on the outside of the cuticle ; that in every phatics. That of the lacteals is to convey the nourishing parts of case of apparent absorption, the epidermis had been in
the food into the circulating system ; that of the lym- jured, or that the matter absorbed had been mechani-
contact with the skin.
giæ, tom. v.
warm bath ; and this augmentation of weight was
+ La Mada longs almost exclusively to the action of the lympha In other experiments again, as iu those of Gerard and
Currie, there was no increase of weight; but the body
is to be considered as a disease, depending on the inability of the stomach to propel the solid food into the
Mr Home, in the paper we have already quoted, (N° 161-169), relates a curious instance of habitual ru-
Of was not observed to have lost any thing during immer- ever, cutaneous absorption is denied ; and, when forced or Absorption. sion in the warm bath.
to confess that there are cases where the egesta exceed Absorption. Now, during these experiments, the body was doubt- the ingesta in a much greater proportion than the waste less wasting, by the pulmonary and cutaneous discharges, of the body will explain, and which can only be acand yet the weight of the body either continued un counted for by absorption, they refuse this function to changed; or where a loss of weight was observed, this the skin, and bestow it most liberally, and, in so far as was constantly less, greatly less, tban is experienced du we know, most gratuitously, on the lungs. We are ring the same interval in air. And we might be incli- not entitled, in return, to deny the reality of pulmonary ned to infer, from a truth so general, and so well ascer- absorption, but we may surely be allowed to urge, that tained, an argument in favour of absorption.
there is no proof that the only inhaling organ is in the It might be argued, that the loss of weight amounts lungs ; and there is none against the possibility of cutato little or nothing, because, during immersion, the bo neous absorption. dy acquires more by inhalation than it does or can do in Is it not, on the other hand, proved, by the experithe air ; that the loss by the pulmonary and cutaneous ments of Seguin and Lavoisier, that the exhalation discharges are counterbalanced, or nearly counterbalan- greatly exceeds the absorption by the pulmonary system? ced, by the increased absorption.
And if this is always the case, we cannot explain by Those, however, who deny absorption, will not allow pulmonary inhalation alone, why the egesta should, in us the advantage of this argument. They tell us, that
exceed the ingesta in a much greater prothe exhalation by the skin and lungs is diminished, portion than the waste of body will account for. which sufficiently explains why the body loses less in the We now proceed to examine another class of experiwarm bath than in air. But that the accustomed dis- ments, much insisted on by those whe deny cutaneous charges are suppressed or diminished in the warm or te. absorption; we mean those experiments performed by pid bath, is, we apprehend, far from being proved; immersing a part of the body in solutions of active drugs, and, till this proposition is made good, the argument the absorption of which should be indicated by their uagainst cutaneous inhalation cannot be securely main- sual effect on the system. tained.
Seguin made numerous experiments of this kind with One of Dr Currie's cases deserves farther considera- solutions of muriate of mercury (corrosive sublimate), on
tion. We allude to the case of dysphagia, published by syphilitic patients. And we are informed, that in cases * Medical this gentleman *, in which Mr M. the subject of the where the epidermis was perfectly sound, neither the Report, case, was several times immersed in a warm bath of known effects of mercury on the body, nor any amelio
milk and water, and was weighed when taken out. ration of the venereal symptoms, was ever observed. p. 227.
Mr M. it is true, gained no weight while in the warm He also immersed his own arm in a solution of two
his thirst vanished, and he made water in the same man lation is so rapid, that nothing can enter the vessels from # Cruick
ner as when he used to drink by the mouth. (H) +. without; but at 180 of temperature, the orifices of the
But to return to the case of Mr M Dr Currie exhalants are sufficiently relaxed, and the exhalation at the Absor dents.
himself remarks, that the discharge by orine alone ex the same time so conveniently languid, that the solution
knowledgment of the reality of inhalation ?
But if in tom. iii.
(1) That thirst may be allayed by immersion in water, is fully proved by the experience of shipwrecked mariDers, who, when obliged to take to their boats with very little fresh water, frequently have recourse to bathing in the sea, or covering themselves with a shirt wetted in salt water, and thus quench their thirst, nearly as well as if they had drunk fresh water.