« AnteriorContinuar »
One of the principal differences said by Mialhe to prevail between albuminous bodies dissolved by acid alone, and through the influence of pepsin, the author did not find in gluten-viz., that, on the addition of rennet, they coagulate from the latter acid solutions like milk, to be again subsequently dissolved.
This is said to obtain for all albuminous bodies, as well for dissolved albumen as for fibrin and gluten; but in the author's experiments on the latter substance he never observed a coagulum such as is produced by the action of rennet on milk. On the addition of acid gastric juice to the hydrochloric solution, a precipitate in most instances occurred, but this took place also when an acid alone was used, so that there is in this case no ground for attributing an active part to the pepsin. But Longet gives a distinctive mark, which Dr. Koopmans also observed. Longet states that when peptons are present, sugar cannot be indicated by Trommer's test, as the oxide of copper is then not reduced, while albuminous matters dissolved in acid alone do not hinder this reaction; and he further says that the absorbed peptons retain this property in the vena porta. Hence sngar ought to be conveyed, without being capable of demonstration, from the intestinal canal to the liver. As a proof of the non-existence of a glycogenic function of the liver, this has, however, absolutely no value, as Bernard has plainly pointed out. Bernard always examined the blood after repeated filtration through animal charcoal, by which all albuminous matters are removed, and as a controlling test, fermentation was employed. Longet himself admits that peptons do not hinder fermentation. After some details, into which it is unnecessary to enter here, the author remarks that the more or less perfect reduction of the deutoxide of copper from Trommer's test ought to enable us to distinguish albuminous bodies from one another. Thus ordinary albumen is coagulated by a boiling heat, while albuminous bodies dissolved in a dilute acid, remain in solution at 212°, but are precipitated by sulphate of soda. Peptons, on the other hand, are rendered completely insoluble neither by a boiling heat nor by sulphate of soda, but are retained by animal charcoal.
“Accordingly, if a small quantity of grape sugar, added to an acid fluid, is not indicated on the application of Trommer's test, but if the reaction takes place after boiling, ordinary albumen is present; if this does not ensue until after treatment with sulphate of soda, an albuminous matter modified by acid has been removed; but if filtration through animal charcoal is necessary in order to make the precipitation of deutoxide of copper evident, the presence of a pepton may be assumed, at least if no other matters capable of disturbing the reaction be present in the fluid.” (p. 400.)
Physiologically speaking, the most important change albuminons bodies undergo is, that they are no longer precipitated from the solution in gastric juice when the fluid is neutralized. If they are only molecularly altered by the action of a dilute acid, they cannot be taken up into the blood, since the alkaline reaction of the latter is sufficient to prevent their passage into it. The author details an experiment to show that the fluids of the small intestines have the same influence in preventing the absorption of such a fluid.
From experiments undertaken by Dr. Koopmans, with a view of determining the degree of acidity most effectual in producing the solution of gluten in artificial gastric juice, it was at once evident that raw gluten requires a different amount of acid in order to its perfect solution from albumen. Boiled gluten appeared to be not so exclusively limited to a definite degree of acidity. Thus it was found impossible to obtain the complete disappearance, in gastric juice of equal strength, of both raw gluten and albumen, although the test-tubes were allowed to stand for days together. This was equally the case at the temperature of digestion or at that of the apartment; and Schwann had already found that increase of the degree of acidity did not compensate for the retarding influence of a diminution of temperature.
The author found that between gobo and zo lies the degree of acidity at which most raw gluten, and between and to that at which most boiled albumen, is dissolved. It also appeared that with the same proportion of acid wbich in artificial gastric juice best dissolved raw gluten, the latter became most broken up in distilled water,
In order to ascertain more accurately whether this great difference between these substances really exists, Dr. Koopmans instituted the following experiment; the middle part (containing the rennet glands) of the mucous membrane of the stomach of a pig having been well washed, was cut into small pieces, and digested for some hours with distilled water at a temperature of 100.4°. To portions of this neutral fluid, previously filtered through linen, so much hydrochloric acid was ndded as to give one part of the latter to 900, 500, and 100 parts, thus forming artificial gastric juice with do, do, and no of acid. Similar well-closed, wide-mouthed, glass-stoprered bottles were now, three by three, filled with twenty-five cubic centimetres of these fluids. Four pieces of freshly prepared raw gluten, four of gluten boiled for titteen minutes, and four of albumen boiled for ten minutes, were then Weighed; nine of these pieces were introduced into the bottles, the three others were intended to ascertain, by drying, the original amount of solid matters in the substances used for the experiment. (In three other bottles the loss in legumin was determined in the same manner.)
All these bottles were now kept for seven hours in a water-bath, at an uniform temperature of 100-4°. At the end of this period what remained uudissolved was thrown on filters, and after twenty-four hours was dried ually with the other weighed pieces at 248o.
The frying will suffice to exhibit the manner in which the author onducted his experiments Without reproducing the tables which he 1 4 them, we may state generally that the numbers he obtained
Antirme the results of the experiments already mentioned, in which he determined the most efficacious proportions of acid. In all the experiments therefore, more albumen was dissolved in a relatively B S than in a week acid; on the vther hand, more gluten was castell in alilute acid than where the amount of acid was greater; mother words and which attacks albumen most violently, dissolves
se gluten, and e ra Consquently, a weakly acid gastric juice is prejudicial to the digestion of coagulated albumen, while it may promote the solution of other substances.
The author found albumen to dissolve, without much difference in time, in artificial gastric juice prepared from the stomachs of a calf, sheep, pig, dog, rabbit, goose, hen, tortoise, frog, and bream. So far as this experiment goes, there would therefore appear to be but little modification of the organic constituent of the gastric juice in different animals, though a difference in the proportion of acid would appear to be capable of explaining much. Unfortunately but few analyses of the gastric juice of various animals have been made known; the gastric fluids of man, the dog, and sheep, alone have been more accurately examined. The author borrows from O. von Gruenewaldt the ascertained quantities of free acid in each of these :
HCl. in 1000 parts. Gastric juice, free from saliva, of the dog . . . . . 3.050 Gastric juice, containing saliva, of the dog . . . . . 2:337 Gastric juice, containing saliva, * of the sheep . . . . 1.234
Gastric juice, containing saliva, in man. ..... 0-200 Hence it would appear that much more acid is present in the stomach of the carnivorous dog than in that of the herbivorous sheep; accordingly, Bidder and Schmidt observed that boiled albumen dissolves much better in the gastric juice of the dog than in that of the sheep. The easy digestion of gluten in artificial gastric juice with a very dilute acid therefore affords reason for supposing that vegetable food should be best digested in the fluid of the stomach of the herbivora, but we must recollect that while gastric juice is the pure secretion of the rennet glands, it soon forms part of a very compound fluid, the constituents of which are never exactly similar; thus, though the quantity of acid in the original gastric juice is tolerably constant, in the stomach it may be very different. The same is true also of the nature of the acid: in the pure gastric juice, free hydrochloric acid seems always to occur, in the ordinary digestive fluid it very often cannot be demonstrated, but lactic acid is now present, which is especially indicated in the analyses of the gastric juice of man. In the ordinary digestive fluid, Schmidt found no hydrochloric acid, but lactic acid. On the contrary, the former was the acid present when the secretion of the pepsin-glands was excited, not by food, but by indifferent matter, which acted only mechanically.
O. von Gruenewaldt found the degree of acidity of the contents of the stomach extremely variable in man, and that this appeared to be much influenced by the acid present in the food itself. Thus, he observed that when a countrywoman labouring under fistula of the stomach, on whom he experimented, had eaten rye bread, her favourite diet, containing much lactic acid, there was far more acid in the stomach than during the use of wheaten bread, the reaction of which is neutral. He remarks, in reference to this point, that an egg eaten along with the latter bread remained longer undigested.
• In the sheep, the food is always tolerably dry in the third stomach (psalterium), the greater part of the saliva having been absorbed in the ante-stomachs.
Schmidt also shows, by an experiment, how much the amount of acid in the stomach depends upon the nature of the food. Thus, the gąstric fluid of a dog fed exclusively upon boiled vegetables required more potash to neutralize it than that of one which got meat; while, nevertheless, the proportion of hydrochloric acid was less. Schmidt assumes that the reaction described was owing to the development, under the influence of the saliva, of lactic acid. In the genuine herbivora, however, which use only raw food, such a high degree of acid does not occur, even if the gastric juice is mixed with saliva and food. In the ruminantia, the effect of the saliva does not extend to the contents of the fourth stomach, as the matters metamorphosed thereby are absorbed in the ante-stomachs (Schmidt); in the others, the formation of lactic acid from starch in the stomach is very improbable, as the saliva of man and of the dog cannot change at least raw starch even into sugar (Gruenewaldt), and gastric juice alone exercises no influence worth mentioning upon the amylacea
The conclusion that vegetable food is best dissolved in a gastric juice with dilute acid, 'depends, however, on the transfer of the properties belonging to gluten to the other albuminous matters found in plants; and the assumption that the mode of their occurrence therein does not essentially alter this relation. Thus, being enclosed in cells is of the greatest influence on the entire solution of albuminous matters; bran, for example, is capable of yielding suitable nutriment only in the digestive apparatus of some animals. The herbivora alone extract the albuminous matter, and the fat which is contained in it in great quantity, from its thick-walled cells; dogs restricted to its use die of starvation.
At all events, therefore, vegetable food in general will not be dissolved by the same gastric juice in the same proportion as gluten, except when this substance constitutes the principal ingredient.
Even in this more limited sense, however, this property of gluten is of great importance, not only in reference to the herbivora, but especially to man. The cerealia occupy a prominent place among our articles of food; even if, therefore, all other albuminous matters be less perfectly digested in the human stomach, that of bread may find precisely the conditions most favourable to its solution, in the, under ordinary circumstances, very weak digestive fluid it there meets. The observations of Gruenewaldt and Beaumont have distinctly proved that it is only through the acid occurring in the food, or formed therefrom, that the acid reaction of this fluid becomes in some measure stronger; while in the fasting condition it even passes, through the preponderance of gastric mucus and saliva, into an alkaline state.
It is principally Frerichs who has examined the contents of the stomach under pathological circumstances, and directed attention to the modified digestion of starch, which mostly consisted in the formation of lactic acid, and even of acetic acid; this increased development of acid is generally recognised as pyrosis, through the obstructing influence it exercises on the digestion of food; Frerichs observed a total deficiency of formation of lactic acid in the stomach where much
sugar was present, in two patients labouring under diabetes mellitus. It is worthy of note, that precisely in this disease Bouchardat's glutenbread is borne for a long time with good result.
In order to ascertain whether the great difference in solubility between gluten and albumen, already described, really existed during the process of digestion in different animals, the author undertook the following experiments on pigs as representing the omnivora, and dogs as representing the carnivora. He had hoped to have procured horses, as being the most suitable among the herbivora, but failed. The compound nature of the stomach in the ruminantia, and the small size of rabbits, with the fact that some portion of food always remains, even after long fasting, in the stomachs of the latter animals, he considered would seriously interfere with the accuracy of the investigation. In order that the substances experimented on should be brought under all the conditions which could influence their solution in normal digestion, and that these conditions should operate on all' at the same time and in the same degree, the following plan was devised. Bags of muslin were filled with weighed quantities of freshly prepared raw and boiled gluten and albumen, and these, carefully closed, and distinguished from one another by the introduction of little glass beads of different colours, were passed immediately after one another through the mouth into the stomach.* After some time the animal was killed, the bags were taken out, washed with distilled water, opened, and the contents carefully collected, dried, and weighed. Other portions of the same egg and the same gluten were also dried, and by a comparison of the weights the loss the substances had undergone in the stomach was ascertained.
The results of experiments on six pigs and three dogs are given in a table, and from them the author draws the general conclusion
“That the same digestive fluid does actually in the living animal dissolve unlike quantities of albumen and of gluten, so that if much of the albumen be digested, the loss of weight of the gluten is but small, and vice versa. So far as can be deduced from the experiments made, the quantity of the boiled gluten dissolved is, as was the case in the experiments on artificial digestion, proportionate neither to that of the raw gluten, nor to that of the albumen.” (p. 420.)
In some of the pigs the albumen dissolved better than the gluten; in others, precisely the reverse obtained; but in no case did an uniform solution of both substances occur. In one dog in which the bags had, at the end of four and a half hours, penetrated to the commencement of the large intestine, the quantity of matters dissolved was beyond all comparison the greatest; in this case alone was the albumen entirely dissolved, and the other substances were very much diminished—a result strongly in favour of the digestive power of the small intestines for albuminous bodies also, which has been very prominently put forward, especially by Bidder and Schmidt.
These experiments further show how important this intestinal
It appears to us, however, that by this mode the important element of dae insalivation was dispensed with, an omission which may have affected the solubility of one substance more than another.