On food : four Cantor lectures, delivered before the Society for the Encouragement of Arts, Manufactures, and Commerce / by H. Letheby.

Henry Letheby

Date:: 1868

Credit: On food : four Cantor lectures, delivered before the Society for the Encouragement of Arts, Manufactures, and Commerce / by H. Letheby. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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$'<7's Extract of Malt is an example of this ; and Mr. son has taken advantage of the discovery ot M. Mourics, that the inner layer of bran contains a aogenous digestive principle called cercahn, of the tiire of diastase, and has extracted it, and consolidated A ith sugar, in a preparation which he has named : arated wheat phosphates. Both of these are aids to .iigestion of farinaceous matters. (i'^rrc/Hfcc is a secretion from the entire surface of stomach. It is a transparent liquid, of a pale yellow ur, and of a saline and acid taste. It is much heavier •i water (sp. gr. about 1,020), and it contains from 2 ; percent, of solid mattei-—about 1-7 of which is a ia;irkable nitrogenous organic body, called by Schwann, , discoverer, pepsin. Its peculiarity is, that in the -ence of an acid, it converts almost every description ilbuminous and fibrinous matter into a soluble form . Ibumen, called by Lehmann, peptone, and by Mialhe 'miiiose. It differs from common albumen in many ticulars—it is, for example, more Hquid; it is not filiated by heat, nor by weak spirit, nor by acids, nor most mineral salts ; it is not very prone to decom- ^ition ; and it is capable of dialysis, that is, of transu- tion through animal membrane, and, therefore, of isorption, which albumen is not. The digestive power it is very great, for Wasmann found that an acid luid containing only one part of it in 60,000 of the iution—that is, about one grain in a gallon, was capable dissolving meat; and Lehmann ascertained that 100 i ts of the gastric juice of a dog would digest 5 parts coagulated albumen. Uhe nature of the free acid in gastric juico is some- it doubtful; Lehmann, who has frequently examined says it is lactic acid, but Schwann asserts that he has n found free hydrochloric acid. It may be that the jrides contained in the stomach are partially decom- ed by lactic acid, especially during the process of i lysis, and thus the hydrochloric acid may be accounted When the acid is in too large excess, the digestive ion is abnormal, and so also when it is deficient; hmann states that the best proportion is when 100 vts of the gastric juice is just neuti-alised with 1-27 of ish. onsidering the importance of pepsin as a digestive nt, the preparation of it has become a common afiair rade. In France it is obtained from the stomach of pig by carefully washing it, then scraping off the it mucus membrane, rubbing it down with a little ter, filtering, precipitating the foreign matters with tate of lead, again filtering, and then precipitating e_ excess of lead with sulphuretted hydrogen, after ich it is allowed to stand, or it is warmed, to get rid excess of sulphuretted hydrogen; it is then filtered ce more, and after carefully evaporating to the consist- ce of syrup it is consolidated with dry starch. In this :ntry it is prepared from the stomach of the sheep as lias of the pig, and we have owvpepsina avis s.nd. pejjsina •ci; besides which, tho use of lead and sulphuretted drogen are avoided by precipitating tho foreign tter with alcohol,—pepsin being soluble in weak spirit. I the lecture-table are specimens of Boudault's pepsin, well as those of Mr. Morson, of London, Messrs. irner and Co., and ]\Ir. Claridge, of Warwick, all of lich are also in operation, showing their relative diges- '6 powers on animal fibrin. The pepsin preparations on tho table contain varjnng [(portions of starch, as from 20 to 50 per cent.; but > digestive power of any specimen may be easily tested I putting a dose of tho preparation into a small bottle m half an ounce of water, acidulating with 20 drops ^drochloric acid, and then adding half a drachm of pa boiled egg chopped small, or tho same weight of ^ meat, or 120 grains of the fibrin of blood. On tading in a warm place at a temperature of from 100 |110, tho digestion should be complete in two hours. Iled m this manner. Dr. Pavy found, some time ago, .1 nearly all tho preparations in common uso were inert; not so, however, at the present time, for, a8 you will notice, digestion is proceeding rapidly. I am told that the strongest pepsin is obtained from young healthy pigs which are kept hungry, and are then excited by savoury food which they are not allowed to eat while the infiuence of it is strong upon them, and the secretions are pouring out in expectation of the meal, the animals are pithed. Pepsin, like diastase, is rendered inert by a tempera- ture of from 120 to ISO^Fah.; and, therefore, very hot drinks after a meal are hurtful. Faiicreatic fluid is a secretion from tho pancreas or sweet-bread. Until recently its true digestive functions were not well determined. It is a colourless fluid of a gravity of 1,008 or 1,009. Like the saliva, it is generally a little alkaline, and it contains about 1'3 per cent, of soUd matter, one-eighth of which is a nitrogenous organic substance of the nature of ptyalin or diastase, and is called pancreatin. More than twenty years ago, Bernard proved, what Valentin had long before suspected, that the pancreatic fluid was concerned in the digestion of fatty matters; but he fell into error in supposing that its action was to saponify the fat, and to set glycerin free. Here is a specimen of glycerin and of lead-soap obtained from fat upon which the pancreatic fluid had previously acted, showing that saponification had not been effected. The true action of the pancreatic secretion is evidently to break up the large granules, and crystals and globules of oil and fat, into myriads of minute particles of from l-3,000th to l-15,000th of an inch in diameter. In this way the fat is emulsified and converted into a milky liquid, which mixes freely with water, and passes through tho tissues of the intestines into the lacteals. We are indebted for this knowledge to Dr. Dobell, who had long been of opinion that the functions of the pancreas were important in certain diseases, and required elucidation. With the assistance of Mr. Julius Schweitzer, of Brighton, the then manager of the laboratory of Messrs. Savory and Moore, he made a large series of investigations into the properties of the pancreatic secretion, and he found that when the fresh pancreas (and best of the pig) is rubbed down in a mortar with twice its weight of hog's lard, it rapidly emulsifies it; and on adding about four or five times the bulk of water, and straining through muslin, there is obtained a thick milky liquid, of the con- sistence of cream, which gradually consolidates. If this be treated with ether, the pancreatised fat dissolves ; and when the ether is separated by distillation, there remains the purified pancreatised fat, wliich is still miscible with water; in fact, when mixed with four or five parts of water it forms the creamy emulsion which is used diet- etically and medicinally in doses of a teaspoonful at a time. The properties of the pancreatic fluid have been well described by Dr. Dobell, in a paper recently read before the lloyal Society of London; and it would seem that the fluid has not only tho remarkable property of emulsi- fying oil and fat, and so rendering them capable of ab- sorption, but it has also the power of dissolving starch by converting it into glucose. In this respect its action is like that of saliva, but it is much moi'e energetic ; for in its fresh state, one part of tho pancreas will dissolve eight parts of starch, and oven after it has emulsified fat it will dissolve two parts of starch. It is, therefore, a powerful agent of digestion, in so far as fat, and starch, and young cellulose are concerned, but it has little or no action on albuminous substances. I am indebted to Dr. Dobell and to Mr. Morson for the specimens oipancrcatinvcaA.pancrcatized fat upon the table. Tho first of those preparations is obtmned by treating the fresh pancreas with water, and carefully evaporating the solution to the consistence of syrup, and then consolidating it with the flour of malt. Perhaps the dried pancreas, powdered and mixed with malt, would be a stronger preparation. Tho liikSs a complex liquid, consisting of biliarj' acids$