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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$n (globulin), which has a romarkahlo property of fib- bing oxygen when exposed to the air, and of giving ait again'in the presence of reducing agents. In the ' cnso it acquires an arterial tint, and in the other a lous; and the spectrum informs us that these two juditions of it arc easily assumed—one hy the presence f atmospheric oxygen, and the other hy decajnng or- anic matter. It is hardly to ho doubted that these e the conditions of it in blood—the bright red oxydizcd ruorin being the form of it in arterial blood, and_ the ark reduced variety of it in venous. The functions, lerefore, of both cruorin and myochrome are entirely f a respiratory nature; for, in the former case it is the ledium whereby oxygen is absorbed from the air in the ings, and is carried with the blood-discs thi-oughout le body, and in the latter it may be the agent of inter- dtial oxydation. Lastly, there is a mineral constituent of our food, silica, 'hich enters into the composition of all the tegumentary ppendages. Its presence is not of so much importance ) us as to the lower animals, whose warmth is retaiued y a natural covering of hair, or wool, or feathers. In le case of birds, indeed, the quantity of siliea in the lathers is very considerable, and Gorup-Besanez has dc- cribed its physiological relations. As to the proportions of mineral substances required 1 the food, it is difficult to spe;ik. Dr. Edward Smith lys that an adult man requires daily from 32 to 79 rains of phosphoric acid; from 51 to 175 grains of hlorine (equal to from 85 to 291 grains of common .t); from 27 to 107 grains of potash; from 80 to 171 f soda ; from 2'3 to 6'3 of lime ; and fr-om 2-5 to 3 of lagnesia. According to Mr. Lawes, a very small por- on of these salts is retained in the system; for in ittening pigs he found that of every 11 lbs. of mineral latter contained in the food only twelve ounces were ;ored up in the body, and this was chiefly the earthy ihosphates, all the rest being either imabsorbed, or else sed in the work of absorption, assimilation, and secre- .on. In most cases, therefore, there iij sufiicient saline latter, excepting common salt, in all ordinary food ; but >r all this, the presence of it in the water we di-ink is ot an unimportant question. Four-fifths of the earth's urface are composed of calcareous strata, which yield rater that is more or less rich in carbonate and sul- ihate pf lime; and it may well be that this is a wise Tovision for the supply of these salts to the animal ystem. As Mr. Johnston has truly observed in his Chemistry of Common Life, The bright sparkling ard waters which gush out in frequent springs from ur chalk and other lime-stone rocks are relished to rink, not merely because they are grateful to the eye, ^ut because there is something exhilarating in the excess f carbonic acid they contain and give off as they pass hrough the warm mouth and throat; and because the me they hold in solution removes acid matters from !ie stomach, and thus acts as a grateful medicine to the pstem. To abandon the use of such a water, and to rmk daily in its stead one entirely free from mineral tmtter, so far from improving the health, may injure it; I fact the water of a country may determine the diet of ■a inhabitants. The soft waters of the lakes of Scot- und, for example, may liave had something to do with 10 choice of brown meal; and but for the calcareous 'atera of Ireland the potato could not have become a ational food. • ^ ''^^^'^ ^^^^ ^^^'^ °^ subject, it is ignt that I should say a few words respecting the func- .ons of certain beverages (as tea, coffee, and fermented quors), which have been more or less in use iii all ages, s It Irom an untaught phy.siological instinct. Vngotable ilUBions, containing the same active principles—name] v stnngont matter, volatile oil, and a crystallizablo body ch m nitrogen, have boon resorted to for some undefined ^n^f 7r T T^'J''^'''' ''^■y '^l™^^ ; ■■'^decd, to use the 'ords of Ur. Johnston, the practice has prevailcdoqually I tropical and in ai-ctic regions. In Central America, the Indian of native blood, and the Creole of mixed European race, indulge alilje in their ancient chocolate. In Southern America tho tea of Paraguay is an al- most universal beverage. Tho native North Amencan tribes have their Apallachian tea, their Oswega tea, their L ibrador tea, and many others. From Florida to Georgia in tho UniCed States, and over all tho AVest India Islands, tho naturalised European races sip their favom-ite coffee; while over the Northern States of the Union, and in the British provinces, the tea of Chiaa is in daily and constant use. All Europe, too, has chosen its prevaUing beverage; Spain and Italy delight in chocolate; France and Ger- many, and Sweden and Turkey, in coffee; Eussia, Hol- land, and England, in tea—whilst poor Ireland makes its warm drink of the husks of the cocoa, the refuse of the chocolate-miUs of Italy and Spain. All Asia feels the same want, and in different ways has long gratified it. Coffee, indigenous in Arabia or the adjoining countries, has followed the banner of the Prophet, wherever in Asia or Africa his false faith has triumphed. Tea, a native of China, has spread spontaneously over the hiU country of the Himalayas, the table lands of Tartary and Thibet, and the plains of Siberia; has climbed the Altais, overspread all Russia, and is equally despotic in Moscow as in St. Petersburg. In Sumati-a, the coffee-leaf yields the favourite tea of the dark-skinned population; while Central Africa boasts of the Abyssinian chaat as the indigenous warm drink of its Ethiopian people. Everywhere, in fact, unintoxicating and non-narcotic beverages are in general use among tribes of every colour, beneath every sun, and in every condition of life. The custom, therefore, must meet some universal want of our nature, some physiological fimction which science has not yet explained ; and, considering that these beverages contain essentially the same chemical compounds, it is remarkable that they should have been selected from the whole range of the vegetable kingdom. As Mr. John- ston truly observes, What constitutional cravings common to us all have prompted to such singularly uni- form results! Through how vast an amount of unrecorded individual experiences must these results liave been arrived at! Tho principal constituents of these vegetable substances are:— 1st. A volatile oil, on which their aroma depends, and which rarely amounts to one part in 150. 2nd. An astringent acid, of the nature of tannic acid in tea, and called caffcic acid in coffee, which give them their bitter styptic taste ; it amounts to from 13 to 18 per cent, in tea, and to about 5 per cent, in coffee; and 3rd. A crystallised nitrogenous substance of an alkaline nature called Theiiic or Caffeine, and Theobromine. Tho averago amounts of this allcaloid in different vegetable substances, according to Dr. Stenliouse, is here recorded:— Thcino or CafTeino per cent. Guarana or Brazihan cocoa, from Guarana 1 - officinalis I Good black tea 2-13 Black tea from Kemaon, E. 1 1-97 Dried coffeo leaves 1-26 Jlate or Paraguay tea from Ilex FarafftMi/. \ , cnsis f '■'■^^ Various samples of coffee-beans from 0-8 to l-QO . The physiological properties of this substance, and of its homologuo, theobromine, are not clearly discoverable. Mulder states that they arc not tho agents concerned in the peculiar action of tea and coffee. Licbig, however, poinLs to tho fact that with tho addition of oxygen and the elemouts of water, they can yield tam-ino, which is l ie nitrogeniscd constituent of bile ; and ho asks whether thoy may not bo concerned in tho production of bile, ilioine, ho also states, is related to la-catinine—that re- markable compound, produced in tho -sital process, and$