.^ £ f % s 5 % S 3 S i II IBRARYQ^ \Q1\W ^OF-CAill y0Aavaa UNIVER% ^AO$ANGEl£n> J^ & s ^"^ -^ I 1 S S =o O I § 5 ^jOf-CAUFOgto ^OF-CAIIFOR^ iv&i r £? ^ 1^. Kt # %OJI1V .^OF-CALI ^' - UNIVER% \V\E-UNI\ CONTENTS. BOOK VIII. Vi OF VEGETABLES. : CHAP. I. — page i: •Strudlure of Vegetables. General Olfervations on organized Bodies. — Conftituent Principles of Vegetable Matter,— Structure of Plants. — The Stem.— The Bark. — The Wood. — Tie Pith. — The vafc?., Chap, i.] We Fruit and Seed. 9 coats, as reprefented in plate I. fig. 5. where the young flower appears towards the bottom of the root. V. The fruit confifts of nearly the fame parts as are found in the ftem ; of a _fkin or cuticle, which is a production or continuation of the (kin of the bark ; of an- outer parenchyma, which is the fame fubftance continued from the bark, only that its veficles are larger and more fucculent or juicy. Next the core there is commonly an inner pulp or parenchyma ; and the core is no more than a hard woody membrane, which inclofes the feed. It is to be obferved, how- ever, that the organization of fruit is very various j in fome the feeds are difperfed through the parenchy- matous or pulpy fubftance; in fome, inftead of a core, we find a ftrong woody fubftance inclofing the feed or kernel, which from its great hardnefs is termed the ftone ; in fome, there are a number of feeds; and in others, only a fingle feed, inclofed in a large mafs of parenchymatous matter. VI. The feed is a deciduous part of >a vegetable, , containing the rudiment o.f a new one. The effence of the feed confifts in the corculum or little heart, which is f^ftened to the cotyledones or lobes, and in- volved in them, and clofely covered by its proper tunic. The corculum confifts in the plumula, which- is the vital fpeck of the future plant, extremely fmall in its dimenfions, but increafing like a bud to infinity. The roftellum, however, muft be included, which is the bafe of the plumula; it defcends and ftrikes root, and is the part of the feed originally contiguous to the mother plant. It is commonly fuppofed, and with fome reafon, that the perfect plant, or at leaft all the organization which is requifite to a perfect plant, £xifts in the feed, furrounded by a quantity of farina- ceous xo Generation of Plants. [B- — Succus Proprlm ; its VeJTds and 'Ccurfe. — Bonnet's Experi- ments on the Nourifonent of Plants. — Dr. Hole's Experiments on Fruit Trees. — Bonnet' 's on Fltnveri, &c. THE fluids or juices of vegetables, fays Dr. Bell, ,are of two kinds. < The one is of the fame nature in all the variety of vegetables : die other varies ac- cording to the different plants in which it exifts. The former, which is called the fuccus commitms, when collected early in the fpring, from an incifion made in the birch or vine, differs little from common water*. The latter, which is named thefuccttspfoprius-, pofieffes various properties in various plants, and gives to each its fenfible Qualities. Theje two juices never mingle with each other in the tree, and the latter is found in the vafa frofiria only. < It is not yet ' alcertained, whether :he juices of plants are tranfmitted through vefiels, or cellular fub- fiance. Each fide of the queftion has had its advo- cates, who have fupported their refpettive opinions with probable arguments : but it is to, be regretted, * It has, however, been al'edged to contain a faccharine matter in fome trees, as in the f-j^ar maple, &c. It has likevvife been fup- pofed to contain an acid. Bat, in various experiments which Dr. Belt made on it, he found nothing in it of either kind ; and therefore, where fuch appearances have taken place, he fuppofed them to ar,ife from an adventuious mixture of the fap, and the fuccus Chap. 2.] Vajcidar Syftem of Vegetables. 13 that, on ib interefting a fubject, no conclufloh can be formed from the actual di flection of vegetables. It however feems moil probable, that all the fluids of plants are tranfmitted through vefiels, for the following reafons. i. The exiftence of "oaja propria and vafa fi&ria is difcoverable by the naked eye, and made ftill more manifeft by the niicrofcope. That fuccus pro- prim and air are contained in thefe is evident, and therefore analogy leads us to believe, that the fuccus ccmmunis is alfo contained in veflels. 2. Secretion, of which vegetables have undoubtedly the power, is in no inftance, that we know of, performed without the action of veflels. 3. An experiment, made by Dr. Haks, feems clearly to prove, that the fap is contained within its own veflels, and does not fortui- toufly pervade every interface of the plant. Fie fixed an inftrument round the ftem of a vine, by which its contractions and expanfions could be accu- rately meafured ; but he found no difference in the circumference of the trunk, when the tree was full of fap, and when it was entirely without it, although the inftrument employed was fo nice, as to detect a va- riation of the hundredth part of a finger's breadth. If the fap had been trarjfmitted, without veflels, through the cellular fubftance, this, on the withdrawing of the fap, would have been comprefled, and of courfe the ftem of the tree would have contracted itfelf into •JL fmaller compafs *. * To determine this queflion abfolutely, it may feem, that the moft certain and obvious method would be by injections, the great fource of our knowledge of the anatomy of animals. They have been employed by Bonnet,. Dr. Hope, and others, but the/; have failed. They rife a confiderable way into plants, but as, in different cafes> they take different courfes, from this and other circumftances there is reafon to believe, that their courfe, and that of the fap, are materially different from each other. ' Botanifts i 4 Evptririfatis on tie 'Courje of tit Sdp. [Book V 1 1 1 i c Botanifts have made many experiments to afcertain the courfe of the fap. Early in the fpring, when the fap begins to flow, incifions have been made in the trunk and branches of trees, as^far as the pith j and, in fuch cafes, it has been constantly found, that a larger quantity of fap flower! from the fuperior, than from the inferior margin of the incifion. This cir- cumilance led to the opinion, that in the beginning of the fpring, great quantities of moiftnre are abforbed by trees from the atmofphere, and hence the fource of the abundance of fap *. But this conclufion is found to difagree with the phenomena of nature, from the two following experiments. ' i. Incifions of various heights being made in the flem of feveral plants, their roots were immerfed in a decoction of log-wood. The roots abforbed the coloured liquor, which at length began to flow from the fuperior, and not from the inferior, mar- gins of the incifions ; nor had the liquor extended itfelf much upwards, beyond the margin of the inci- fion from which it was difcharged. { 2. In the feafon wh,en the fap flows moft abun- dantly, called the bleeding feafon^ a deep cut was made into the branch of a growing vine, and the greateft quantity of fap was difcharged from the upper margin of the incifion : but a branch of the fame" tree, cut in the fame manner, being inverted, the fap flowed moft copioufly from the 'other margin of the incifion, which of courfe was now that next the root. On the other hand,* many experiments may be brought to prove direftly, that, in the bleeding fea- fon, the fap afcends from the roots towards the branches ; the following however may fuffice. i. Early * Du Hamcl and others.— See Phyf. des Arbres, Tom, I. p. 67. in Chap. 2.] C'ourjt of tb'e Succus Prcpfius. :*$ in the fpring, when little or no flip had as yet en- tered the plant, Dr. Hope made a number of inci- fions of different altitudes, into the root and ftem of a birch. As the fap rofe, it firft flowed from the fupe- rior margin of the loweft incifion, and then, in regular fucceffion, from the upper margins of the other inci- fions, till at laft it reached the higheft. 2. If, in the beginning of the bleeding feafon, before the fap is found in the ftem or branches, an incifion is made in the root of a vine, a confiderable flow of fap will follow the wound, 3. The quantity of fap is very generally proportioned to the humidity of the foil *. f When a portion of the bark and wood of the pine is cut from the ftem, the Juccus propritis flows in confiderable quantity both from the upper and under margin of the incifion. Hence it occurred to bota- niits, that this juice might have little or no motion, and that its efflux from fuch an orifice might depend entirely on its being freed from the preflure of the bark and wood. But I cannot accede to this opinion i for although, in the beginning, thejuccus proprius flows from both margins of the incifion, in a little while, as I have obferved, it is difcharged from the fuperior * It may ftill be afked, Why the fap flow* moil from the fupe- perior margin of< each inciuou, iuppoliug. it to arife from the roots ? The incifion, it is faid, hurts or deitroys the energy of the fap-veffels fora confiderable way below, whence the lap is not- propelled upwards againil its own weight, and the preflure of the atmofphere now admitted. From the divided veflels, it pafics by a lateral communication (for there aie fap-veflels in every direc- tion) into thofe undivided, and when it has got above the incifion, it again pafTes laterally into the divided veiTels; and falling down- ward*, from its own gravity, a want of continuity of veflels, and the diminifhed preffure of the stmofphere, i: flows from the fupe- rior margin of the incifion. margin 1 6 How Plants are wurifhed. [Book VIIL margin ©nly. This obfervadon in itfelf is not how- ever decifive. For it may be fuppofed, that the liquor flows more copioufly from the fuperior margin, be- caufe the prefiure of the air is lefs upon it, than on the inferior, and becaufe the liquor itfelf is difpofed to fall downwards by its gravity, in the fame manner as the Juccus communls. That I might put this matter out of doubt, I placed the branch of a pine in a ho- rizontal pofttion, and another branch I inverted, fb that its branches were turned towards the earth. In thefe fituations, I cut a portion of the bark and wood from each, and in both inftances, the Juccus proprius flowed only from thofe margins of the incifions which were fartheft from the roots. Hence it appears clearly, that the courfe of this juice, in its veffels, is never from the roots towards the branches^ but always in the contrary direction *.' M. Bonnet conceives that the nutrimental juices of vegetables pafs during the day-time from the roots to the trunk by the ligneous fibres, affifted by the air- veffels, and are principally carried to the furface of the leaves, where a copious perfpiration takes place. At the approach of night the heat no longer ailing on the leaves and the air contained in the air- veffels, the fap returns towards the roots j at the fame time that the* humidity condenfed on the inferior furfaces of the leaves, which by their inequalities are bed fitted to retain it, is abforbed and conveyed through the branches to the trunk. In this manner he is of opi- * From the experiment above recited, it appears, that the flow of the proper juice is not influenced in the fame degree, as that of the fap, by an alteration in the pofture of the veffels fcom which it itfues. To what caufe this is owing, does not clearly appear. nion €hap. 2;] Experiments on Fruits. 17 nion that vegetables are nourifhed in the day- time by their roots^ and in the night by their leaves. The fame philofopher wifhed to difccr/cr whether plants nourifhed by their leaves would live as long, and thrive as well, as others nourifhed by their roots. He plunged in fmall veffels, filled with water, plants of mercury, immerfing the leaves of fome and the roots of others. Pie left to each plant one or two fprigsi which were kept out of the water, and which were only nourifhed by the part of the plant which was immerfed. He rendered all thefe fprigs as equal and as much alike as poffible. He left the plants in this fituation for five or fix weeks, at the end of which time he could obferve no difference between the fprigs uniformly nourifhed by the leaves, and thofe .nourifhed by the roots. He only remarked that the leaves plunged in water feemed to fuffer a little more from the aclion of that fluid than the roots. M. Bonnet alfo buried the top of a willow-tree, leaving the roots above ground. The roots being prevented from drying by a covering which did not entirely ex- clude the air, piit forth leaves mixed with roots ; the top, which was buried in the ground, produced roots* and the plant continued to live. Dr. Hales, in his ftatical experiments, mentions fe- veral in which he tried to change the natural flavour of fruits, and to communicate thofe of fevcral fpiriruous liquors, and of different odoriferous infufions. With this intention he plunged in different liquors branches loaded with fruit j and left them there for fome time, without being able to perceive that the tafte of the fruits was in the leaft altered, whether the experiment was made upon them ripe or unripe. But he almoft always perceived the fmell of the liquors or infuiions in the ftalks of the leaves, and in the wood. He VOL. III. C conjectures, 1 8 Experiments on Flowers. [Book VI IL conjectures, with much probability, that the veflela near the fruit become fo fine as not to admit the odo- riferous particles. M. Bonnet made experiments on flowers fimilar to thofe which Dr. Hales made on fruits. He chofe fuch flowers as have naturally little perfume, as the different fpecies of French-beans. Stems with thefe flowers were immerfed in tubes, fome of which were filled with fpirits of wine, others with Hungary water, &c. In about twenty-four hours the flowers were faded,, and they had already acquired in a very fenfible de- gree the odours of the liquors which they had im- bibed. The odour became much more remarkable a few days afterwards. M. Bonnet alfo found that the leaves of the apricoutree acquired a fenfible edour from the liquors into which branches e-f that tree were plunged,. - 3-1 I 19 C H A P. III. FUNCTIONS OF VEGETABLES. erfpiration of Plants.*— Circulation of the Fluids in.Plants, — Property in Plants of emitting vital Air ; of decomps/ing^atfr.^— Senftbility to the Sun 's Light,**- Caufe of the Green Colour of Vegetables.—*- Bennetts "Experiments en 'Vegetable Perfpiration. — Sexual Syjtcm.-— Growth and Nutriment of Vegetables,— Manures.—- Principles of Agriculture. H J£ leaves of plants have been not improperly compared with the lungs of animals. * Plants •as well as animals,' fays an author whom I have already quoted with approbation, c perfpire, and in both cafes this function is effential to health. By the ex- periments of Dr. Haks *, and M. Guettardf, it ap- pears, that the perfpirable matter of vegetables differs in no -refpecl: from pure water, Excepting that, it be- comes rather fooner putrid. The quantity perfpired varies, according to the extent of the furface from •which it is emitted, the temperature of the air, the time of the day, and the humidity of the atmofphere. As the leaves form the greateft part of the furface, it is natural to fuppofe, that the quantity of thefe will very materially affect the quantity of the perfpiration. Ac- cordingly, the experiments of Dr. Hales have afcer- Iteined, that the perfpiration -of vegetables is increafed or diminiftied, thiefly, in proportion to .the increase or diminution of their foliage J. Th« degree of heat in which the plant was kept, according to the fame * Statical Effays, vol.i. p. 49. •f Mem. de 1'Academie des Sciences, 1748. J Statical Effays, vol. i. p. 2-;. C a author^ io Odoriferous Exhalation from Plants. [Book VIII; author, varied the quantity of matter perfpired ; this being greater, in proportion to the greater heat of the ibrrounding armofphere. The degree of light has Hkewife considerable influence in this refpeft : for Mr. Philip Miller's experiments prove, that plants uni- formly peripirermoft in the forenoon, though the tem- perature ofthd'.air, in which they are placed, fhould be unvaried. M. Guettard likewife informs us, that a plant, expo fed to the rays of the fun, has its per- fpiration increafed to a much greater degree, than if it had been expofed to the fame heat, under the lhade. Finally, the perfpiration of vegetables, is in- creafed in proportion as the atmofphere is dry, or in other words, diminimed in proportion as the atmo- iphere is humid.' Dr. Hales found that a fun-flower, weighing three pounds, perfpired twenty-two ounces during twenty- four hours. Dr. Keil perfpired thirty-one ounces in twenty-four hours. The quantity therefore perfpired by the fun- flower was much greater, in proportion to its weight, than that perfpired from the human body. Dr. Kei! ate and drank four pounds ten ounces in twenty-four hours. Seventeen times more nourifhment was taken in by the root of the fun- flower, than was taken in by the man. If the perfpiration of vegetables is checked, they fpeedily fade. I: is checked from glutinous fubftances adhering to their furface; hence the advantage of wafhing them. The more healthy and vigorous the plant, the more copious the perfpi- ration j though an excefs, as well as a defect of it* feems prejudicial and even deftruftive to vegetables. Ik bears alto a proportion to: the quantity of leaves, ^.efe being the principal organs of perfpiration. The odoriferous exhalation of leaves and flowers forms an atmofphere around vegetables, which ftrikes our 'Chap. 3 . ] Circulation of t'he Fktias . 21 our lenfes, and which the contact of -a body of fire is fometimes capable of inflaming, as has been obferved with regard to the fraxinella. c Some botaniits, obierves Dr. Bell, f have con- ceived, that plants, as well as animals, have a regular circulation of therr fluids. Others think this very im- probable. Or, both fides, recourfe has been had to' experiments ; and from thefe, conclufions pierfeclly oppofite have been deduced. When a ligature has been fixed round a tree, in fuch a manner that no juice could be tranfmitttd through the bark, the tree has been found to thicken above the ligature ; but below it, to continue of the fame circumference. Hence fbme Jiave -concluded, that the fap afcends through the wood, and defcends through the bark, Thofe who are of a contrary opinion have found, that, in certain cafes, the juice afcends through the bark only: for v/hen a portion of the wood has been cutout, and the bark exactly replaced, the growth of the tree has been found to go on unchanged : hence it, is faid, that the juice is tranfmitted equally through all parts of vege- tables. The experiments adduced on each fide of the queftion are juft, but the reafonings on thefe, by each party, feem equally inconclufive. The analogy of ani- mal nature appears to favour the opinion, that the juice rifes through the wood only, and defcends only through the bark ; but this analogy is not complete through- out. The arteries are not placed in the internal parts alone, nor the veins in the external, but they accom- pany each other through every part of their diftribu- tion. In, vegetables, th« fap rifes from the roots, but the proper juice defcends towards them -, in the defcent of the juice, the wood acquires its growth, and ab- ibrption is a conftant aftion of the leaves. Thefe cb- lervations render it probable, that there is a circulation 22 Vital Energy of Plants. [Book VII L of the juices i and if there is, the veiTels which perform it, we may reafonably believe, accompany each other through every part of their co.urfe,' By what force the juices of plants are propelled in their circulation, remains yet one of the fecrets of nacure. It has been attributed to capillary attraction,. bur this caufe leems inadequate to the effect j nor is it poiTible on ihat principle to explain why the fap of the vine flows from an incifion made in the fpring, and not from one made in the fummer. The capillary attraction ought not to be lefs powerful in the latter than in the former fcafon j indeed it ought to be more fo, as the heat is greater. Befides, capillary tubes do not difcharge their contents when broken acrofs j but from the ftem of a plant cut tranfvcrfelyj a large quan- tity of fluid is difcharged. The more probable opi- nion is, that plants are endued with fomeuhing of a vital power or energy, which impels the juices through the whole vafcular fyftem ; and this opinion is ftrength- cntd by an obfervation of Dr. Bell, which wa* the re-, full of experiment, namely, that there are particular fubftanres which increafe the growth of plants, by acting asftimilbnts on their fibres. The expeiiments of Dr. Prieftley have fufficiently fhewn that vegetables have the power of correcting bad air; and Dr. Ingenhouz has proved chat they nave the faculty of producing vital air only when acted on by the rays of light. If a vegetable is immerfed in water, and the rays of the fun directed on it, air-bub- bks will be obferved to collect on the leaves, and at length rife to the furface of the water. This appear- ance is moft remarkable in the morning, as the leaves have not then been previoufly exhaufted by the action of light. Vital air of a great degree of purity may bfe obtained in the fummer time, by inverting a jar i filled Chap. 3.] Bad Air correfted by Vegetation. 23 filled with water .in fuch a manner as to receive the air- bubbles as they arife. All plants, however, do not emit this air with the fame facility; there are fome which emit it the moment the rays of the fun act upon them, and this is the cafe with lavender. Some aquatic plants afford vital air with great facility, fome more (lowly, but none later than in eight or ten mi- nutes, provided the fun's light is ftrong. The air is almoft entirely furniihed by the inferior furface of the leaves of trees; herbaceous plants afford it from almoft the whole of their furface. The leaves afford more air when attached to the plant, than when ga- thered, and the quantity is greater, the frefher and founder they are. Young leaves afford but a fmall quantity of vital air; thofe which are full grown afford more, and the more the greener they are. The epi- dermis, the bark, and petals do not afford it, and in general vital air proceeds only from thofe parts of plants which are of a green colour. Thus gr.~en corn and green fruits afford this air, but it is not produced by thofe which are ripe ; and flowers in general render the air noxious. Thefe facts may tend to explain the manner in which the light of the fun operates in ma- turing fruits, viz. by expelling the fuperfluous oxygen, and thus changing them from a harfh and four, into a mild and fweet fubftance. Aquatic plants, and fuch as grow in moift places, are remarkable not only for affording a large quantity of vital air, but alfo for ab/ ibrbing inflammable gas, and are therefore in all re* fpects calculated for purifying the air of marmy fitua- tions. A very extraordinary power of abforbing in-' flammable air was obferved in the willow by Dr. Prieflley ; and this fact feems connected with the ra- pid growth of that plant in marmy fituations, where much inflammable air is produced. M. Sennabier C 4 found 24 Pure Air -produced by Plants in Water. [Book VIII, found that plants yield much more vital air in diftilled water impregnated with fixed air, than in fimple diftilled waser. It appears further, from the experiments of Dr. Prieftley, that plants will bear a greater proportion of inflammable than of fixed air, and that vital air ap- peared generally injurious to plants. A.fprig of mint growing in water, placed over a fermenting liquor, and of courfe expofed to fixed air, became quite dead in one day ; a red rofe became of a purple colour in twenty four hours. Plants die very foon both in ni- trous air, and in common air when faturated with it. Air appears uniformly to have been purified by heakhy plants vegetating in it ; but thefe experiments require great nicety, as the lead degree of putrefaction will injure the air. The -air contained in the bladders of marine plants was found confidcrably purer than com- mon air. Armofpheric air is reftored, after being injured by refpiration or combuftion, by a plant vegetating in it. This reiteration of air depends upon the vegetating ftate of the plant; for a number of mint-leaves- frefh gathered being kept in air in which candles had burnt out, did not reftore the air. Any piant will effect this purpofe, but thofe of the quickeft growth in the moil .•rious manner. That plants have a proper' y of producing pure air from water is evident from an experiment of Dr. Prieftley. The green matter which is to be obferved .i-.er is doubtiefe a vegetable production. Water containing this green matter always afforded vital air in a-largv: quantity, but water which had it not afforded none. It has been frequently- rbferved that vegetables do not thrive in the dark, A receiver was therefore j with water, and kept till it was in aftate of giving air Chap. 3.] Ufe of tie Green Slime In Water. 1$ air copioufly ; after this it was removed into a dark room, and from that time the production of air en- tirely ceafed. When placed again in the fun, it afforded no air till about ten days after, when it had more green matter, the former plants being probably all dead ; and no air could be produced till new ones were formed. From various experiments it appeared, that different animal and vegetable putrefcent fubftances afforded a very copious pabulum for this green vegetable mat- ter, which produced fo freely the vital air; whence the philofophic author of this difcovery is led to the following conclufions— c It is impoffible,' fays he, c not to obferve from thele experiments the admirable pro- vifion in nature, to prevent or leffen the fatal effects of putrefaction, t fpecially in hot countries, where the rays of the fun are mod direct, and the heat moil in- tenfe. Animal and vegetable fubftances, by limply putrefying, would neceffarily taint great maifes of air, and render it unfit for refpiration, did not the fame fubftances, putrefying in water, fupply a moft abundant pabulum for this wonderful vegetable fubftance, the feeds of which feem to exift throughout the atmofphere. By thefe means, inftead of the atmofphere being cor- rupted, a large quantity of the pureft air is continually thrown into it. By the fame means alfo, ftagnant wa- ters are rendered much lefs offenfive and unwholfome than they would otherwife be. That froth which we obferve on the furface of fuch waters, and which is apt to excite difguft, generally confifts of the pureft. vital air, fupplied by aquatic plints. When the fun fhines, this air may be obferved to iflue from them. Even when animal and vegetable lubftances putrefy in air, as they have generally fome moidnre in them, various other vegetable productions* in the fon l6 Plants forbade do not afford good Air. [Book VIII. mold, &c. find a proper nutriment in them, and by converting a considerable part of the noxious effluvia into their own fubftance, arreft it in its progrefs to cor- rupt the atmofphere.1 The fame vegetables which afford vital air very plentifully in the light of the fun, afford in the fhade air lefs pure than that of the atmofphere. This ftrik- ing effect of light on vegetables is a ftrong argu- ment in favour of the opinion, that the motion of the juices of the vegetables is performed by veffels, which, like thofe of animals, poiTefs irritability, and are excited to action by ftimulating lubftanceS. The effect of vegetation in producing the vital air, which was afforded in the preceding experiments, leemed in fome meafure dubious to Sir Benjamin Thompfon, who extracted vital air, by immerfing in water a variety of Jubilances, as raw filk, cotton, wool, eider down, hare's fur, fheep's wool, ravdlings of linen, and human hair — as related in a former book. He was led, from the refult of thefe trials, to fufpect that the ;?nre air was merely feparated from the water, and th.n any fubitance which would act by a capillary at- traction, fo as to feparate ti.e component parts of the water, would effect the production of pure air. He therefore procured a quantity of (pun glafs, which con- fifts of minute tubes., which he immerfed in water, but the quantity of pure air produced was very trifling. Hence he concludes, that there is fomething in thole fubftances which operates in producing pure air, and fhat it is not merely a mechanical reparation of the component parts of water. The light of lamps produced the fame effect as the ^iun's light, air in great quantities was produced, and perfectly pure. Vegetables will alfo, with any ftrcng light, produce vital air as well as with the light of the fun. Chap. 3,] Senfilility of Plants to Light, 27 fun. The air from filk was much fuperior to that from, vegetables. Plants have a remarkable fenfibility to light; they unfold their flowers to the fun, they follow his courfe by turning on their ftems, and are clofed as fo. n as he difappears. Vegetables placed in rooms where they receive light only in one direction always extend them- felves that way. If they receive light in two di regions, they direct their c.ourf" iowards the ftrongeft. Trees growing in thick forefts, where chey only receive light from above, direct their (hoots almoft invariably up- wards, and therefore become much taller and lefs fpreading than fuch as (land fingle. This arTectioii'for light feems to explain the upright growth of vege- tables, a curious phenomenon, too common to be much attended to. It has been afcertained by repeated ex- periments, that the green colour of plants is entirely owing to light ; for plants reared in the dark are well known to be perfectly white. If we take a fucculent plant, and exprefs its juice, the liquor appears at firft uniformly green ; but allow it to ftand, and the green colour feparates from the watery fluid, and falls to the bottom in a fediment. If we collect this fediment it will be found to be of an oily nature, for it dues not diflblve in water, but it will in fpirits of wine, or oil, to which it imparts a green colour. As the fun produces the green colour in plants, and as this refides in an oily matter, it was formerly concluded that light furnimes the oily matter of ve-. getables, and that it effects this by furmfhing the prin- ciple of inflammability. The new chemical do Brines, however, afford a much more fatisfactory explanation of the effect of the fun's rays in producing the oily matter in vegetables. Vegetable matter confifts in general of carbon, hydrogen and oxygen -3 the lun's rays produce 2S Toe Sexual Syftem. [Book VIII. produce a difengagement of the latter principle in the form o,f vital air, and the two former are the confti- tuent principles of oil M. Bonnet made a feries of experiments in order to afcertain whether the fuperior or the inferior furfaces of leaves have a greater fhare in performing perfpira- tion. From the trials which he made, he concludes that the inferior furfcce of the leaf is in general by far the moil active in this refpect, though in one or two tpecies of vegetables this difference was much lefs re- markable. The mallow was the only vegetable the leaves of which perfpired more by the upper than the inferior furface. The method which he employed to afcertain the comparative effect of the two furfaces was to cover firft one and then the other furface with oil. The leaves were then immerfed in tubes filled with water, and the quantity of the perfpired matter was cteafured by the length of the tube emptied in a given time. The oil, by flopping up the pores, prevented perfpiration from the furface to which it was applied. Some large leaves of the white mulberry-tree being kept fufpended on water with their upper furfaces in contact with the fluid, faded in five days ; fome leaves of the fame x tree, being placed in a fimilar fituation, but with the inferior furface touching the water, were preferved green for nearly fix months. The fexual fyftem has been the fafhionable fyflem of botany for many years. It is well known that the palm is of that clafs of vegetables which has flowers of different fexes on different trees. The peafants in the Levant, whether acquainted with this fact, or whether directed to the practice by accident alone, have been accustomed to break branches from the male palm while in flower, and attach them to the fjsmale plant, which they find to be conilantly productive of an abun- dant Chap. 3. J Experiment on the Tal-n. 29 dant crop. This faft has alib been proved by a moft decifive experiment of M. Greditfch. There was in the royal garden at Berlin a beautiful palm'-tree, a fe- male plant, which, however, though twenty-five years old, had been always barren. There was another palm at Leiplic of the male kind, which bloflbmed every year. This ingenious botanil]:, undertook to fecundate the palm at Berlin from that at Leipfic, and had fome of tne^loflbms conveyed by the poll. The confequence was, that he produced that leafon excel- lent dates ; and the experiment profecuted with fome variation for feveral iiicceeding years, was attended with the fame iuccefs *. It has been faid, that the pollen was deftined for the impregnation of the germen* This is performed in the following, manner. The . antherae, which at the firft opening of the flower are whole, burft foon after, and difcharge the pollen. Being difperfed about the flower, part of the pollen lodges on the furfacc of the ftigma, where it is detained by the moifture with which that part is covered. Each fingle grain or atom of the pollen has been obferved by the micfof- cope to burft in this fluid, and is fuppofed to difcharge ibmething which impregnates the gsrmen below : what the fubftance is which is fo difcharged, and whe- ther it actually pafies through the ftyle into the germen, feems yet undetermined, from the great difficulty of obferving fuch minute parts and operations. In fome vegetables, the ftamina move towards the -pift ilium j and a very evident motion of them is obferved in the flowers of the common berberry, on touching them •with the point of a pin. * Bonnet Contemn, p. 6. The 30 Paiutuvi of Plants, [Book VI 1 1, The NoukiSHME T of vegetables, as it is fo inti- mately connected with the important fcience of agri- culture, has defervedly attracted confiderable attention. Mr. Boyle dried in nn oven a quantity of earth proper for vegetation, and, after carefully weighing it, planted in it the feed of a gourd ; he watered it with pure rain-water, and it produced a plant, which weighed fourteen pounds., though the earth had fuffered no fen- fible di Miration. A \vjiiow-tree was planted by Van Helmont, in a. pot, containing 100 pounds of earth. This was in ge- neral watered with diftilled water, or fometimes with rain-water, which appeared perfectly pure. The vefiel containing the plant was covered in fuch a manner as totally to exclude the entrance of all folid matter. At the end of five years, upon taking out the plant, he found it to have increafed in weight not lefs than 1 19 pounds, though the earth had loft only two ounces of its original weight. Thefe experiments would admit of fome doubt, and mult have remained in a great meafure inexplicable, but for the experiments of Mr. Cavendim, and the facts related by Dr. Prieftley, which place it beyond a doubt, that vegetables have a power of decompofing water, and converting it, with what they derive from the atmofphere, into almoft all the different matters found to exift in their fubftance. For the products of wood in diftillation, 1 muft refer the reader to what has been advanced in the chapter on carbon, or the carbo* naceous principle. All the proper juices of vegetables depend on the organization, as is evident from the operation of graft- ing. From the materials of fimple water and air, arc produced thofe wonderful diverfities of peculiar juices and fruits, which the vegetable world affords > and the immenfe Chap. 3.] Pabulum cf Plants. 31 immenfe variety of taftes, fmelfs, &c. In the fame vegetable what a variety is found ! The bark is diffe- rent rn tafte from the wood, the peculiar juicas have ibmething different from them both, and the pith of plants affords a matter which could not have been ex- peeled from their exterior properties. The root is often different from the item, and the fruit from both, in all their fenfible qualities. In whatever way the nourifhrnent of vegetables is received, it may fairly be faid to confift principally of water. I am inclined to believe, however, that cal- careous earth, in fmall portions, may enter into the compofition of at leaft many vegetables; fmce animals which exift entirely on vegetable food are found to have in their folid parts, the bones for inftance, a con~ fiderable portion of this fubftance ; though it muft be confefTed, that chemical analyfis, as far as it has hitherto- gone, does not warrant us in fuppofing calcareous earth to be an cflential conftituent of all vegetable matter. It may be faid further, that on fcme occa- ftons the addition of other matters, as of different kinds of manure, adds greatly to the growth of vegetables; but in whatever degree a rich foil or durig may add to the luxuriance of growth, other facts feem to prove that it is not effential to vegetation. It is well known that many herbs fiourifh in pure water, and that pear, plum, and cherry trees, planted in pure mofs, have arrived at fuch perfection as to produce good fruit *. .Different * It is but fair to infert the following' fa&, which feems to fa- vour the neceffity of carbonic matter to the growth and increafe pf at leaft fome fpeciesof vegetables. f< M. Ruche rt is pcrfuaded that earth and wpter, in proper proportions, form the fole nutriment of plants; but M. Giobert ias clearly ftiewn the contrary ; for, having mixed pure earth of 32, Operation of Manures. [Book VI I L Different theories have been advanced, to account for tne operation of manures in promoting the growth of vegetables, none of which feem altogether fatisr factory. The common opinion is, that the fubftances employed a^ manures are the food of plants, and are abforbed by their roots. This hypothefis may be true to a certain extent, when applied to forne manures, but cannot be true with regard to them all ; for it is well known, that riot only chalk and lime, but even flints, are very beneficial to fome foils. Another opinion is, that manures act by bringing foils to fuch a confiftence as is favourable to the growth of the roots of vegeta- bles, and to the affording of them water in a proper quantity. A third opinion is, that manures act as fti- muli on the roots of vegetables, and thus excite them to more vigorous action. Some authors think that manures act as folvents on matters previoufly contained in the foil, and thus fit them for entering the roots of plants ; and others, that they act chemically, by form- ing combinations which are favourable to vegetation; "Which of thefe hypothefes is beft founded, it is difficult to determine j but it does not feem unlikely that they may be all true to a certain extent.- When we attempt to difcover the component prin- ciples of the objects around us, and the fources whence they are fupported, we are loft in the greatnefs and diverfity of the fcenes prefented to us. We fee animals nourifhed by vegetables, vegetables apparently by the remains of animals, and foffils compofed of the relics allum, -filex, calcareous earth, and magnefia, in various propor- tions, and moiftened them with, water, he found that no grain would grow in them ; but when they were moiftened with water fronk a dunghill, corn grew in them profperoufly. Hence the jieceffity of the carboi.ic panciple is apparent:"— Kir^an oft Manures, p. 42. of Chap. 3.] Principles of Agriculture. 33 tof both thefe kingdoms. It is certain, however, that ve- getables muft in every part of the globe have preceded animals. A feed of mofs lodging in a crevice of a bare rock is noufiftied by the atmofpherei) and the moifture afforded by the rains and dews. It comes to perfection, and fheds its feeds in the mouldering remains of its own fubftance. Its offspring do the fame, till a cruft of vegetable mould is formed fufEciently thick for the flip- port of grafs and other vegetables of the fame growth. The fame procefs going forward, fhrubs, and laftly, the largeft trees, may find a firm fupport on the once barren rock, and brave the efforts of the temped. From the advantages derived from a change of -crops in agriculture, it has been fuppofed that different vegetables derive different kinds of nouri foment from the fame foil, feleding what is beft adapted to their own fupport, and leaving a fupply of nourifhment of another kind for vegetables of a different fpecies. Was this, however, the cafe, vegetables would not fo much impede each other's growth when placed near toge- ther. And in the operation of grafting, we have a clear proof, that the juices received by the root of one fpecies of tree may, by the organization of the inferted twig, be fubfervientto the growth of leaves, flowers, and fruit of a different kind. The advantage derived from a change of crops may be better explained on other principles : fome plants extend their roots hori- zontally on the furface of the foil, others ftrike them downwards to a confiderable depth. Some plants are t found to bind or harden the foil, others to loofen it. Thus, for example, wheat and rye -grafs render a foil ftiff, while pulfe, clover and turnips pulverize it. By varying the crops, therefore, the foil is preferved in a middle (late, between too much ftiffhefs and too much friability. Nor is this the only good effect arifmg from VOL. III. D that 34 Change of Crops. [Book VIII. this difference of roots. From this circumflance fome vegetables draw their nourifhmcnt from the furface of the earth, while others derive it partly frcm a greater depth. So that by a change of crops, a larger portion of the foil is made to contribute to the nourilhment of plants than could have been effected by the cultivation of any fingle fpecies. One other advantage to be de- rived from a change of crops, is this : fome plants extract almoft the whole of their nourifhmenc from the •foil ; and this is particularly the cafe with thofe which are moil valuable, and which contain the greateft quan- tity of folid matter. By the repetition of fuch crops, however, the foil is found to become too much ex- haufted. There are other plants which derive a large proportion of their nourifhment from the air ; by fuch therefore the foil will be much lefs exhaufted, and un- "der a crop of them will be in fome meafure at reft. The good effects of a change of crops may therefore be fufficiently explained, without fuppofing that each particular fpecies of vegetables is nourilhed by a differ- ent kind of food. This opinion is alfo neceffarily attended with two great difficulties : one is, that there exifts in every foil as many diftinct kinds of nourish- ment, as there are fpecies of plants capable of growing, in that foil j the other, that plants are endued with the faculty of difcerning and.feleeting, from all thefe kinds, their own proper nourifhment. The former of thefe fuppofitiohs is too abfurd to merit the leaft attention, and the latter has been difproved by actual experiment, lince plants are not able to prevent their roots from absorbing fuch matters as prove poifonous to them. Other writers, however, have been more moderate, and though they have rejected the idea of fpecific nou- rifhment in general, have neverthelefs imagined that the hypothecs might be well founded with relpect to Chap. 3,] Specific Manures. 35 to particular fpecies of vegetables. This they infer from the exiftence of ipecific manures, as foot for faintfoiri, afhes for white clover, and fome others. It does not fcem poffible, however, to draw a line of .diftincliion j and if we reject the idea of a fpecific nourifhment in general* we cannot admit it in parti- cular inftances. In order to difcover whether plants have an aflual power of diftinguifhing matters prefented to their roots, a friend, who affifted me in compiling this part of the work, made, among others, the following expe- riment. • A vigorous plant of mint was placed in a two- ounce phial, filled with filtrated well-water, to which were added four drops of a moderately ftrong folu- tion of fal martis. On examining the plant the fol- lowing day, no other effect was obfervedj than 'that the very tips of the radicles were withered and black. Four more drops of the folution were now added. On the third day the appearances were the fame ; and no new change taking place on the fourth, twelve more drops of the folution were added. On the fifth day the roots appeared of a yellowiih green colour, and the top drooped very much. The larger leaves were pretty much withered and blackened. The abforp- tion of the water appeared to be in fome meafure impeded, but not entirely prevented. On the fixth 'day the whole plant was withering very faft; the roots became of a dark olive-green colour, and the larger leaves were become very black, efpecially tho. foot-ftalks and the projecting fibres. On the feventh day the blacknefs had made ftill further progrefs, and the plant was dead. A fufficient proof that fome of the iron was abforbed by the plant, may be drawn from the following circumftance— its leaves when ma- D 2 cerated 36 -Fallow Land. [BookVlIL cerated in diftilled water, produced a black colour •with galls. The leaves of a plant of mint, which had been nourlfhed by water alone, when tried by the fame teft, produced no colour whatever. Trifling as this experiment may appear, it proves two points; that plants have not the power of rejecting even inju- rious matters when prefented to their roots -f and that other matters befides water and air are capable of being abforbed'by them* Agriculture feems yet to be nearly in its infancy, and even the benefit produced by the common cuftom of letting lands lie fallow, has not yet been fatisfacto- rily explained. Something may no doubt be attri- buted to the deftrudtion of weeds, but more probably to fome change produced in the foil by its being ex- pofed to the action of the fun and air. The manage- ment of nitre- beds may tend to throw fome light on this fubje<5t. Thefe are compofed of calcareous earth and dung cemented together. After being expofed for fome months to the air, they are found to contain a quantity of nitrous acid, which, uniting to the cal- careaus earth, forms a kind of fait, which is extracted by lixiviation. Now calcareous earth .and dung are two of the molt powerful kinds of manure, and it doe;! not feem improbable that their fertilizing powers may be in fome manner connected with tlieir property &f affording nitrous acid. Chap. 4-]- [ 37 ] CHAP. IV. VEGETABLE SUBSTANCES. Of the mofl remarkable Vegetable Productions. — Vegetable Qxyds.* Vegetable Adds.-r-Otber ejfintial Salts of Vegetables. IT has been already remarked, that the fimple com- ponent principles, which are eflential to the forma- tion of vegetable matter, are but three in number, namely, carbon, hydrogen, and oxygen. From the various proportions in which thefe ingredients are combined, refults almoft all the variety of vegetable matters which fall under our notice. Sugar, mucus (under which term I include the different kinds of gums, and flarch) are vegetable oxyds, having hydrogen and charcoal combined, in different proportions, as t.heir radicals or bales, and united with oxygen, fo as to bring them to the ftate of oxyds. From the ftate of oxyds they are capable of being changed into that of acids, by the addition of more oxygen } and accord- ing to the degrees of oxygenation, and the propor- tion of hydrogen and charcoal in their bafis, they form the feveral kinds of vegetable acids. On the other .hand, gum by being deprived of oxygen is capable of affording oil. M. Woulfe has found that a pound of gum arabic diftilled with a quarter of a pound of vegetable alkali, furnifhes a conliderable quantity of .oil. The liquor which rifes along with it is not at all acid; therefore the acid of the gum re- mains united with the , alkali. Honey afforded copi- oufly an oil, when fubmitted to the fame procefs. Pj The 3S Vegetable Actts, [Book Vli f , The following are all the vegetable acids hithertc* known. 1. Acetous acid, or vinegar. 2. Oxalic acid, or that of forrel and fugar. 3. Tartarous acid. 4. Pyro *, or empyreumatic, tartarous acid. 5. Citric acid, or that of lemons. 6. Malic acid, or that of apples. 7. Pyro-mucous acid. 8. Pyro-ligneous acid. 9. Gallic acid, or that of galls. jo. Benzoic acid, or that of gum Benjamin. 11. Camphoric acid. 12. Succinic acid, or that of amber. Nitrous acid, repeatedly diftilled with gums, muci- lages and fugar, is decompofed, the azote in part cfcapes, and the oxygen uniting with the inflammable matter of thefe fubftances, produces the acid of fugar. By a continuation of the procefs, however, the hy- drogen and charcoal of the mucilaginous matters are feparaiied ; the charcoal, combining with the oxygen, forms caironic acid gas, and the hydrogen either efcapes in the (late of inflammable air, or, attracting part of the oxygen, forms ware r. From this view of the lubject, together with other tacts, it has been inferred, that a greater or lefs proportion of vital air, united with the other two general principles of vegetables, hydro- gen and charcoal, produces all the various acids of vegetables. Thus tartar is faid to have been con- verted into the acid of apples, by treatment with * Pyro from the Gre^k tiv^ (fire) means any thing prepared or extradited, by fire.— Empyreumatic has the fame etymology and meaning. ,nitrous Chap. 4.] Vegetable Acids. 39 nitrous acid. The acid of apples, by the continu- ance of the operation, becomes converted into acid of fugar, or acid of forrel, which are the fame thing. The fame procefs further continued, affords vine- gar. Hence it fhould feem that according to the greater progrefs of the operation of combuftion, or the combination of vital air with the bafis, the acids of tartar, of apples or unripe fruit, of forrel or fugar, of vinegar, and laftly of charcoal, are pro- duced. In this order of proceeding, the/ acids be- come more and more perfect, and lefs eafily de- compofable; and it probably proceeds from this caufe, that the reverfe of thefe procefles could never be completely accomplifhed. Profeffor Murray, of Gottingen, has affured us, that he has obtained acid of fugar by repeated diftilla- tions and congelation, without ufmg nitrous acid. Abbe Fontana obtained an acid perfectly like that of fugar from all the gums and relins. Mr. Watt of Birmingham, when making fome experiments relative to ink, obferved a number of particles floating in the fluid, which had the fhape of cryftals of the faccharine acid, and upon examihatiqn were found to be really fuch ; and, conducting the procefs in the ufual way with the nitrous acid, he found that aftringent vegetable matters contain the acid of fugar in greater abundance than that fublhnce from which it derives its. name. . Thefe faline matters are called eflential falts of ve- getables. There are fome others which are alfo called eflential falts, but are not peculiar- to vegetables. Such as the fixed vegetable alkali, which may be extracted by incineration from plants in general, and the fixed foffil alkali, which is only extracted from D 4 marine 4© Neutral Salts found in Vegetables* [Book VIII. marine plants. Several neutral falts rmy alfo be ex- traded from particular vegetables : as vitriolated tartar from niillefoil, and from aftringent a.nd aromatic plants; Glauber's fait from tamarifk ; coma en fi!t and mu- riat of pot-afh from marine plants. M.iny other falts •will doubtlefs be found, when a greater number of plants fhall be accurately analyfed, Chap. 5.] [ 41 ] CHAP. V. OF THE MORE SIMPLE VEGETABLE COMPOUNDS. um.— Gum Arabic. — Gum Tragacanlh. — Common European Gum.—- Sugar', obiained from moji Vegetables.— Procefs of ma.tcingSngar.-~— Manna — Fat, or exprejj'ed Oils. — Chocolate.'— Vegetable IVax Analyfis of Olive Qil.-^-E/entiel Oils.— Of Cinnamon.— Of Bain, Peppermint and Wormwood.— Of Lavender . — Of Rofes.—Of Anifeed. — Of Par/ley. — Of Camomile. — Of Saflafras and Carra- ^way. — Of Nutmeg, Pepper and Mace. — Balfams. — Balfam of Tolu. — Benzoin and Storax. — Camphor. Re/ins.— Gum Copal. — • Catchouc or elajlic Gum..-r-Fecula. — Briony.— Potatoes. — Sago. — Salep. — Farina cr Flour. — Gluten. — Starch. — Saccharine Matter of Wheat. — Bread. — Colouring Matters of Vegetables. — Principles of the 'Art of Dying. — Arnotto. — Baftard Saffron. — Archil. — Indigo. — Alkanet Root .—Luteola. — -Madder.— -Walnut.— Alder,— » Sumach, &c. — Galls.— Lakes. THERE are certain compound fubflances, which are formed by the procels of vegetation, and may be obtained without the application of any greater heat than that of bciling water, or the action of any other folvents, than water and ardent fpirit. Thefe fubflances may be referred to the following heads: — i. Gum. 2. Sugar. 3. Fat Oils. 4. Ef- fential Oils. 5. Balfams. 6. Camphor. 7. Refin. 8. Pure fecula of vegetables. 9. Farina. 10. Vege- table colouring matters. I. GUM.— Its characters, when in its pureft ftatc, are thofe of a fubftance inodorous, infipid, generally folid? of more or lefs tranfparency, with fometimes a flight 42 Gum. [Book VIII. flight tinge of colour, generally yellow ; eafily foluble in water into a vifcid liquor, called mucilage, in which ilate it originally exifted in the vegetable j not acted on by fpirit of wine or oils j not volatile in the heat of boiling water, nor fufible in any heat, but fubject to the fame changes as other vegetable matter. Gum, in its dry and folid ftate, is not in the leaft acted on by oils, but mucilage manifefts a confiderable dif- pofition to unite with them. Gum is not a folvent of refmous or balfamic matter ; this matter will, how- ever, be difTolved in water, in confequence of being added to gum, efpecially by the afiiftance of agitation. Thus oils and balfams may in many cafes be combined with water, and remain combined with it, forming a milky folution, particularly if the quantity of gum is confiderable. This kind of combination is very fre- 1 quent in plants. There are many in which oil and gum, are naturally united. The ufeful juice of the poppy is of this kind, and from fuch compounds gum-refins are obtained, by the evaporation of their watry parts. Thefe compounds have full fallibility in water, though the gum is the part chiefly difiblved; the refmous part is either left in its concrete ftate^' or being merely fuf- pended, and not difiblved, its particles are interpofed between thofe of the gum and water, and occafion a degree of opacity. Such fubftances alfo in their folid ftate as confift of a mixture of gum and refin are al- ways opake, while the pure gums and pure refins have more or lefs of tranfparency. Gum is very abundant in the vegetable kingdom ; it is found in a great number of roots -3 the young Ihoots and young leaves contain it in large quantities, and its prefence may be known by ics vifcous and ad- hefive quality, when thefe parts are crufhed between the ringers. Gum is ufually obtained by wounding 6 the Chap. 5.] Gum Arabic, We. 43 the bark of particular trees. ' Ic is obfervable, that fao chcirine fruits, when four and unripe, are found to con- tain gum and an acid; whence it {eems not unfair to conclude, that faccharine matter is formed of thefe ma- teri. Is, operated on by the procefs of vegetation. The moft common gums are— i. Gum Arabic, which flows from the acacia in Egypt and Arabia, and is of the fame nature with gum Senegal, which is fome- limes fold inftead of it. 2. Gum tragacanth, which is obtained from a thorny bufo, growing in Crete, Afia, and Greece. 3. The gum which flows from certain trees growing in this country, particularly apricot and plum-trees. The efTential characters of all thefe gums are the fame, but gum tragacanth is by far the moft powerful in producing a thick and tenacious mucilage. II. SUGAR. — The mixed and various properties of this fubltance, have rendered chemifts very doubtful to what clafs of bodies it ought to be referred. By fome it has been called inflammable, by others faline, and by others it has been clafied among gummy and mucilaginous matters. Sugar is foluble, both in water and ardent fpirit. It is more inflammable than gums, and has not been proved to contain any fait ready formed, except fome fixed alkali. It is the only prin- ciple the prefence of which enables fluids to take on the vinous fermentation. Saccharine matter is found in a great number of ve- getables j fuch as the maple, the birch, the red beet, the parfnip, the grape, farinaceous grain, potatoes : Margraff indeed extracted it from moft vegetables ; and it is well known that honey is a faccharine matter, collected by the inftincl: of' the bee from an infinite variety of plants, but principally from flowers. The pundo faccharifera or fugar-cane contains this matter however 44 Boiling of Sugar. [Book VIII. however in larger quantities, and affords it more readily, than any other plant. The ripe canes are twice crushed between iron cylinders, by which they are fqueezed completely dry, and fometimes even reduced to powder. The cane juice or melaiTes is received in a leaden bed, and thence conveyed into a veffel called the receiver ; thence it runs to the boiling-houfe, where it is received into a copper pan or caldron, which is called a ciarifier. Of thefe there are generally three, and their dimensions are determined by the extent of the owner's planta- tion. Methods of quick boiling are indifpenfably ne- ceflary, as the pureft cane juice will not remain twenty minutes in the receiver, without fermenting and be- coming tainted. As foon as the flream from the re- ceiver has filled the boiler or c|ariper with frefh liquor, and the fire is lighted, the temper, which is generally Briftol white lime in powder, is ftirred into it. This is done in order to neutralize the fuperabundant acid, to get rid cf which is the great . difficulty in making fugar. As the force of the fire jncreafes, a fcum is. thrown up, which proceeds from, the gummy matter of the cane, with fome of the oil, and fuch matters as are entangled in the mucilage. The heat is now fuffered to increase gradually, till it approaches to that qf boil- ing water; but it mult by no "means be fuffered to boil. When the fcum begins to rife into biifters, and break into white froth, which generally appears in about forty minutes, it is known to be fufficiently heated. The fire is then extinguifhed, and, if circumftances will admit, the liquor is left a full hour undifturbed. The liquor is now carefully drawn of, fo as to leave the fcum, and conveyed by a gutter to the evaporating boiler ; and if produced from good materials, and well managed, it will appear almoft tranfparent. In this ycITel it is fuffered to boila and the fcum as it riles is continually Chap. 5/j Mufcmado Sugar. 4$ 'continually taken off, till the liquor becomes finer, fome - what thicker, and almoft of the colour of Madeira wine Being transferred to a fmaller copper, the boil- ing and fcumming are continued.; and if the liquor is not fo clear as might be expected, lime-water is ad* ded, which thins the mixture, fo as to fuffer the im- purities to rife more' readily to the furface. When, in confequence of fuch fcumming and evaporation, the li- quor is fo reduced that it can be contained in the third copper, it is laded into it, and fo on to the laft copper, "which is called the teache. This arrangement fuppofes four coppers, befides the three clarifiers. In the teache the liquor undergoes another evapo- ration, till it is fuppofed to be boiled enough to be re- moved from the fire. The cooler (of which there are generally fix) is a fhallow wooden veflel, about eleven inches deep, feven feet in length, and from five to fix feet wide. A cooler of this kind holds a hogmead of fugar. Here the fu- gar grains, that is, as it cools it runs into a coarfe irre- gular mafs of imperfect cryftals, feparating itfelf from the melafles. From the cooler it is taken to the cur- ing-hp'ufe, where the melaffes drains from it. When it is cooled fo that the finger may be plunged into it without injury, it is poured into barrels, placed over certain cifterns, and pierced at the bottom with many holes, imperfectly (lopped with the ftalk of a plantain leaf, through which the fyrup drains. In the fpace of three weeks the fugar becomes tolerably dry and fair. It is then faid to be cured, and the procefs is finifhed. The fugar thus obtained is called mufcovado, and is the raw material whence the Britifh Tugar-bakers chiefly make their loaf or refined lump. The juice of the fugar- cane contains a fuperabundance of acid, which prevents the dry concretion, In order to get rid of this, 46 Clayed Sugar. [Book VTli. this, they employ lime-water, as the faccharine acid is feparated by its means from every other combination* The lime powerfully atrracYing the acid whtn united with it, forms an infoluble fait, which either falls to the bottom or mixes with the fcum. Many perfons have fuppofed that a portion of the lime remains mixed with the fugar ; but Bergman allures us, that if the purification is properly conducted, the nature of the ingredients, the circumftances of the operation, and finally the moft accurate analyfis, abundantly mew, that there is not the fmalleft trace of lime remaining. Good fugar difiblves totally in diftilled water, which could not pofiibly be the cafe if there was prefent any lime, either in a feparate flate or united with the fac- charine acid. There is another fort of fugar, which is much tifed, and which in England paries by the name of Lisbon fugar, but which in the Weft Indies is called clayed fugar; the procefs for making it is as follows: — A quantity of fugar from the cooler is put into conical pots or pans, with the point downwards, having a hole about half an inch in diameter at bottom, for the me- lafTes to drain through, but which is at firft flopped with a plug. As foon as the fugar in thefe pots is cool, and becomes a fixed body, which is known by the middle of the top falling in, the plug is taken out, and the pet placed over a large jar, intended to receive the fyrup which flows through. In this ftate it is left as long as the melaffes continues to drop, when a ftratum of moiftened clay is fpread on the fugar. The water gradually draining from the clay, dilutes the melaffes, in confequence of which more of it comes -away from the fugar, which becomes whiter and finer. A fecond covering of clay is put on when the firft is dry, and water is again fuffered to filter through, after which the Chap. 5.3 Manna, 47 the loaves are carried to an oven to dry. At the end of eight or ten days thefe loaves are broken, and the powdered fugar is conveyed to Europe. Certain juiqes which flow out of plants are of a fac- charine nature ; fuch is manna, which is produced by the pine, the fir, the oak, the maple, the juniper, the fig, the willow, &r. ; but the afli; the larch, and the alhagi afford it in the largeft quantities. Robel, Ron- delet, and others, have obferved at Montpelier, upon the olive trees, a kind of manna, to which they hare given the name of oeliomeli. Tcurnefort collected it from the fame trees at Aix and Toulon. The am, which is very abundant in Calabria and Sicily, affords the manna of commerce : it flows fpontaneoufly from thefe trees, but is much more abundantly collected by making incifions in the bark. That which is procured by introducing chips of wood or fmall flicks into artificial apertures, forms a kind of ftalactites, perforated within, and called manna in the tear. Manna in flakes flows from the bark, and contains fome impurities. Manna affords, by treatment with the nitrous acid, the fame acid as is obtained from fugar. III. FAT OILS are not emitted from the furface of vegetables, but are obtained by prefiure from their emulfive feeds or kernels. They feel fmooth to the touch, are generally, when recent, without fmell or tafle, and are infoluble in water. They are not vola- tilized but by a heat confiderably fuperior to that of boiling water, and do not take fire till fufficiently heated to be volatilized. When they are burned on the wick of a lamp, fmall portions are fuccefllvely brought to its extremity, and being there volatilized, undergo in- flammation. Moft fat oils are fluid, and require a con- fiderable degree of cold to congeal them -, others be- come 45 Vegetable Wax. [Bock Vllf* tome folid by a very flight degree of coU ; and others again arc almoft always folid : thefe laft are called nut- ters. Such are thofe of the cacao nut, from which chocolate is made, and alfoofthe cocoa-nut. Vegeta- ble wax is of the lame nature, only more folid. It is the production of China ; and is there made into yel- low, white, or green candles, the colour varying accord- ing to the manner in which the wax is extracted. The catkins of birch and poplar afford a fmall quantity of a fimilar wax. M. Berthollet eafily whitens if with oxy- genated muriatic acid. Fat oils expofed to the air attract its oxygen, and become acid or rancid. Water and fpirit of wine, by abftracting this acid, deprive them of their ftrong tafte, but never completely reftore them to their original ftate. M. Bertholict has difcovered that fat oils, thinly fpread on the furface of water, and expofed to the air, become thick, and aflume the appearance of wax. This appears to arife from the abforption of oxygen, as the oxygenated muriatic acid produces this change more fuddenly. Thefe oils afford by diftillation a fmall quantity of \vater impregnated with a peculiar acid, a light oil, a denfe oil, and inflammable and fixed airs. The quan- tity of charcoal left behind is not abundant. By re- diftilling the firft products-, more- water, and an oil which becomes lighter each time, are obtained. La- voifier collected the products of olive-oil burned in an apparatus properly conftrudted to afcertain their na- ture and properties. He obtained feventy-nine parts cf carbon, and twenty- one of hydrogen, from one hundred of oil. From thefe component parts, infer- ences may be drawn refpecting the acid, the water, the fixed air, and the inflammable air, afforded by partial decompositions or combuftions of this fluid. When oils Chap. 5.] Compofit'ion of Fat Oils. 49 oils are burned in pure air, one of their component , principles, hydrogen, is combined with pure air, and forms water j while charcoal, its other component part, combines with pure air allb, and forms fixed air. The denfe animal oils, fuch as butter, tallow, fat, and the oil of the whale, exceedingly refemble vegeta- ble fixed oils. They appear, however, to contain a proportion of azotic air and animalized matter, pro- bably in the ftate of ferum or jelly. Agitation in water feparates a mucilaginous matter from fat vegetable oils, which feems to be the caufe of their becoming rancid. They combine with pure fixed alkalies into foap, and they alfo unite with magnefia and lime, which form with them foapy compounds. IV. ESSENTIAL OILS are remarkable for a ftrong aromatic fmell, and are fufficiently volatile to rife with the heat of boiling water. They are in general foluble in fpirit of wine, and their tafte is very acrid. They are much more inflammable than the fat oils. Effential or volatile oils exift in moft fragrant vege- tables, and in various plants are found in different parts; thus the oil of cinnamon is found in the bark ; of balm, peppermint, and wormwood, in the leaves ; of the rofe and lavender, in the flower j of nutmegs, anife, and fennel, in the feeds. They are obtained either by ex^- preflion, as from the peel of oranges and lemons, or by diftillation with water. For the latter purpofe, the plant is put into a copper alembic, with water •, the water being made to boil, comes over together with the oil into the receiver, and is obtained feparate by decanta- tion. Some of the eflential oils are fluid, as that of laven- der ; others congeal by cold, as that ofannifeed; others are always concrete or folid, as thofe of rofes and parfley. They differ much with refpe6t to colours : thus, oil of VOL. III. E lavender 50 Ejfential Oils. [Book VUL lavender is yellow, that of cinnamon deep yellow, that of parfley green, that of camomile blue. Some of the eflential oils float in water, as moft of the oils obtained from plants growing in temperate cli- mates ; others, as thofe of faflafras and carraway- feeds, and moft of the oils from hot countries, fmk in that fluid. This property is not, however, invari- able witlvrefpect to climate, as the efiential oils of nutmeg, pepper, and mace, are lighter than water, ft is remarkable, that eflential oils fometimes entirely differ in their properties from the plant which affords them ; thus, oil of pepper is mild, and oil of worm- wood is not bitter. The perfume, or principle of fcent, in plants, to whkh Boerhaave gave the name of Jpiritus rfffer, feems in general to refide in the eflential oil. It compofes an extremely fmall part of the weight of vegetables, as may be inferred; from the lofs of fra- grance fuftaincd by eflential oils with little or no lofs of weight. It does not fcem improbable, that the perfume, or principle of fcent, in plants, is a gas of a peculiar nature. Its invifibility and volatility, the manner in which it is expanded and difperfed m the atmofphere, together with certain experiments made by Dr. Ingenhouz, on the noxious gas af- forded by flowers, render this opinion very pn> bable, It is eafy to difcover the adulteration of volatile oils, either by pouring ardent fpirit on them, which will not diflblve the fat oil they may be contaminated with ; or if they are dropped on paper, and held to the fire, the eficntial oil evaporates, leaving the fat oil behind, whkh makes a greafy fpot. If oil of tor- pendne is fraudulently added to them, its fmell be- ttays its prefence when treated in this manner. By cxpofurc Chap. 5%] Baffams. .51 expo fore to the air they become thick, and in procefs Of time affurhe the character of refin. Needle- fhaped cryftals are depofited fimilar to thofe afforded by camphor when fublimed. Geoffrey the younger obferved them in the effential oils of motherwort, marjorum, and of turpentine. The fame chemift ob- ferves, that their fmell is fimilar to that of camphor. Effential oils combine very readily with fulphur, and form compounds called balfams of fulphur, in which the fulphur is fo far changed that it cannot be recovered. V. The proper vegetable BALSAMS are oily aro- matic fubftances, imperfectly fluid, obtained by inci- cifions made in certain trees. The word balfam has been ufed in a very extenfive fenfe, to denote a variety of vegetable fubftances, which agree in confidence, though differing very widely in their nature and pro- perties. This denomination, however, is more pro- perly confined to fuch refmous matters as poifefs a fragrant fmellj and more efpecially contain acid, odo- rant, and concrete falts, which may be extracted by decoction or fublimation ; fuch as benzoin, balfam of Tolu, and ftorax. VI. CAMPHOR is a peculiar vegetable fubftance, of a ftrong fmell and tafte, which refembles efTential oils in fome of its properties* and differs from them in others. It is much more volatile than the effential oils; with the moft gentle heat it ftiblimes and chryftalizes in hexagonal laminae attached to a middle ftem. By a fudden heat it melts before it rifes. Water does not diilblve it j but it is plentifully foluble in fpirits of wine, aether, and concentrated acids, from the two former of which it is feparated by the addition of water without alteration. Fixed and volatile oils diflblve I£ 2 camphor S-2 Campbof. [Book VI It, campfior with th \vhich are of an extractive or faponaceous nature, are readily difiblved in water. The colouring principle of many other fubfiances refides in a purely refinous matter, infoluble in water, and in fome inftances at- tached to matters infoluble, even in fpirit of wine j but they are all acted on by alkalies, which convert them into a kind of foaps, mifcible with water. The prin- cipal colours of this nature are the annotto, a kind of fecuk, obtained by maceration of the feeds of the urucu putrefied in water, and which dyes an orange yellow colour ; Chap. 5,] Art of Dying, 59 colour j the flower of carthamus or baflard faffron, •which affords a very fine red ; archil, which is a pafte prepared with mofifes, macerated in urine with lime, and which dyes red, The colour of indigo alfo refides in a refmous matter. Certain colouring fubftances are fbluble in oils. Al- kanet, or the red root of a kind of burgjofs, is of this kind, but cannot be ufed in dying. We may eafily conceive that a coloured decoction may ftain any (luff which is dipped into it, and that this colouring matter may be again abftracted by the applica- tion of the fame menftruum as it was originally fufpended in. But the action of thofe dyes, which, although once diflbl ved and fufpended in water, cannot again, after they are applied to fluffs, be wafhed out, is not fo eafily under- ilood. Thefe latter, or durable dyes, alone deferve atten- tion. Dyes of different colours require different treat- ment. Stuffs to be dyed of a red or yellow colour muft be boiled in water, with alum or fixed alkali, before they are dipped into the dying decoctions : the red colour- ing materials are kermes, cochineal, gum^lac, and mad- der ; the yellow materials are luteola or dyers weed, and other yellow flowers. The fluffs for b&e dyes re- quire no previous preparation. Thefe blue dyes are made of indigo, or the blue fecula obtained from -woad, difiblved in a lixivium of fixed alkali, or in urine, with or without the addition of fome green vitriol. The (luffs intended to receive a root colour, require no pre- vious preparation, but to be foaked in warm water. Thefe dyes are chiefly decoctions of walnut-itiells, wal- nut-roots, alder-bark, fumach, and launders. Thefe root colours, which are all yellow, ferve to form a very good ground, on which other more brilliant colours may be applied, and to them no faline or other matter is added. The black dyes, which are inks or decoctions 6 of 60 Theory of Dying. [Book VIII, of galls, mixed with green vitriol, require no previous preparation of the fluff. It is obfervable that wool takes the dye better than filk, filk than cotton, and cotton than flax. Writers on the art of dying hold different opinions refpe£t- ing the manner in which colouring particles apply them- felves to the fubftances expofed to their contact. Many have fuppofed that this application takes place only in proportion to the number and magnitude of the pores in the various fubftances. Macquer, who has paid great attention to this fubject, fuppofesthat the greater or lefs facility with which the colour is applied, de- pends on the refpective nature of the colouring parts, and the fubftances propoled to be dyed : and that dying is truly an external tinge or painting, which fucceeds and lafts by virtue of an affinity and intimate union between the colour and the dyed fubftance. This ferves to explain the ufe of the matters, which it is on many occafions neceffary that the fluffs fhould imbibe, previous to immerfing them in the dying fubftance, The fame thing may be illuftrattd by confidering the procefs employed in the preparation of certain colours called lakes. Vegetable colouring matters are diffolved, and then precipitated by the addition of fome other fub- ftance. Thus, for example, if madder is boiled in wa- ter, together with an alkali, and alum is then added, the earth of the alum will be precipitated, together with the colouring matter, with which it will form an infoluble pigment. A double decomposition here takes place, the vitriolic acid quits the earth of alum to unite with the fixed alkali, and the vegetable matter unites itfelf with the earth, Chap. 6.] [ 6 1 ] CHAP. Vt. FERMENTATION. Kinds of Fermentation.— The vinous or fpirituous.— Spirit of Wine or Alcohol.— ~Etber, — Acetous Fermentation. — Putrid Fermen- tation.-—Obfer-vations on Putrefaflion in general. HAVING confidered the ftructure and compo- fition of vegetable fubftances, it becomes ne- ceflary to direct our attention to certain fpontaneous changes which they undergo, when deprived of the vi- tal principle. Thefe changes are called fermentations, which are three in number, and are termed, from their products, the vinous or fpirituous, the acetous, and the putrid. The circumftances univerfally neceflary to fer- mentation are moifture, a certain degree of heat, and the contact of air. The three kinds of fermentation are Ibmetimes confidered as different flages of one pro- cefs i this, however, is an improper view of the fubjeft, as each kind of fermentation is a peculiar procefs, and totally different from every other. Some bodies be- come acid without having undergone the fpirituous fer- mentation, and others putrify without fhewing any dif- pofition to afTume either that or the acetous ftate. The conditions neceflary for the production of the VINOUS or fpirituous fermentation are — i. A degree of fluidity flightly vifcid. — 2. The prefence of laccha- rine mucilage. It is found that the fermentable juices of fruits, boiled till they become thick, are indifpofed to ferment, and this not only in their infpiflated ftate, but when diluted again with water : for this reafon it is, that in the making of fugar nothing is of more im- portance than the juice of the cane being fubmitted to boiling 6 i Phenomena of Fermentation^ [Book VIII, boiling immediately on being expreiTed. Preierves, and other mixtures prone to fermentation, are pre- vented from that procefs by the fame method. — 3. A proper temperature, which varies from forty-eight to eighty of Fahrenheit's thermometer. If below this, the fermentation is languid j if above it, it is impetu- ous, and is apt to rum into the acetous ft ate even be- fore the vinous. — 4. The addition of a quantity of the fubftance called yeaft, which is itfelf the product of the vinous fermentation^ is of great afiiftance in exciting it. By what power yeaft acts in producing the vinous fer- mentation, has been much difputed. Mr. Henry thinks that yeaft is ne other than fixed air already formed, but enveloped or entangled in the mucila- ginous matter of the liquor from which it was obtained ; and the fame ingenious experimentalift was able to bring on the vinous fermentation* by adding to com- mon wort a quantity of fixed air in the elaftic form. To account for this, it is not difficult to fuppofe that fixed air has an attraction for its own conftituent prin- ciples, when placed in favourable circumftances to act upon them ; and that it will thus occafion the fepara- tion of fixed air from the fermentable liquor, which is fo remarkable during fermentation. The phenomena which prefent themfelves in a li- quor during the fpirituous fermentation are — Firft, A muddinefs, from the ftparation of an aerial matter, which rifes in bubbles to the top in fuch quantity, and in fuch quick fucceffion, as to produce a hifling noife, and form a froth. Thefe minute globules of air occafion the motion of the particles of the fluid among one another ; and this motion is perceptible, even before the air is vifibly feparated. The globules of air attach themfelves to the particles of the mix- ture, and buoy them up; at length the globule is detached, Chap, 6.] Vinous Fermentation. 63 detached, and the atom finks by its own weight* The nature of the air which is difengaged was not imderftood till the modern experiments on aeriform fluids afforded fo much afiiftance to chemical fcience* It is now afcertained to be the carbonic acid gas, or fixed air, which, being heavier than atmofpheric air, forms a ftratum in the upper part of the veffel in which the fluid is fermenting, where it may be per^ ceived from its greater denfity. This air, contained in the fermenting vats of brewhoufes, frequently pro- duces the moil fatal effects on the workmen j and a candle dipped into it is as certainly extinguished as if plunged into water. During the time that the fer- mentation is going on, the bulk of the liquid is augmented, Another phenomenon is the production of a gentle heat, equal to about feventy-two degrees of Fahrenheit's -thermometer. After fome days, the number of which varies according to the dilution of the fubftance and the degree of heat, the motion in the fluid diminifhes, the warmth abates, and the cmiffion of air is leffened j the liquor becomes clear, and the fcum, which confifts of the more folid par- ticles and air, becomes heavier in proportion as the air efcapes, and at laft finks. The liquor has now undergone a great change ; it has acquired a pungent and pleafant tafte and fmell, and an inebriating quality, and has loft its fweetnefs. If the liquor is now dif- tilled, inftead of an infipid matter, we obtain an ar- - dent fpirit, and a four, grofs fluid remains behind *. By • The phenomena of fermentation have long been known ; but it remained for Lavoifier to afcertain with accuracy what happens in that procefs. I fhall therefore extract his experiments and con- clufions, as Hated by hirofelf, ia his Elements of Chemiftry. T A E L. E 64 'Ardent Spirit. • [Book VIII. By the experiments of Lavoifier, it appears that ardent fpirit (alcohol) or the produdl of the vinous fer- mentation TABLE I. Materials cf Fermentation. libs. oz. gros grs, Water * 400 ooo Sugar - - 100 ooo Yeaft in pafte, IQ libs. $ Water - - 7 3 6 44 compofed of | Dry yeaft 2 12 i 28 Total - 510 o o o TABEE II. Conjlituent Elements of the Materials of fermentation, libs, oz.gros grs> Hydrogen 61 i 2 71.40 Oxygen 346 2 3 44.60 Hydrogen B ooo Oxygen ^4000 Charcoal 28 o o o Hydrogen 045 9.30 Oxygen i 10 2 28.76 Charcoal o 12 4 59 Azote 005 2.94 407 libs. 3 oz. 6 gros 44 grs. of water, compofed of 100 libs, fugar, compofed of" 2 libs. 12 oz. I gros 28 grs. of dry yeaft, compofed of" Total weight -• 510 o o o TABLE III. Recapitulation of thefe Elements. libs, oz.gros grs. > {"of the water 340 ooo ~\ £ \ of the water / libs. oz. gros grs. |V in the yeaft 623 44.60 Wii 12 6 1.36 Q J of the fugar 64 o o o i (_of the dry yeaft i 10 2 28/76 J j f of the water 60 o o o "\ £o\ of the water / S-( in the yeaft i i 2 71 4° > 69 6 o 8.70 T3 l«r*u-r. ° o o o I 4 5 9-30 J of the fugar of the dry yeaft o I: 28 ° ° ° \ 28 12 4 CQ.06 o 12 4 59.00 f of the fugar o/ the yeaft Azote of the yeaft 005 2.94 •« ' In all - 510 o o o ' Having Chap. 6.] Compoffion of Ardent Spirit. 6$ mentation, confifts of the fame principles as fugar, ex- cept that they are combined in different proportions. Ardent fpirit contains more hydrogen, and lefs car- bon and oxygen j which latter principles compole the carbonic acid gas which efcapes during the fpirituous fermentation.' M. Lavoifier found that when ardent Ipirit is burned in a chimney adapted to receive the vapours, a larger quantity of water is formed than the whole of the fpirit employed amounts to ; whence it follows, that ardent fpirit contains a large proportion of « Having thus accurately determined the nature and quantity of the conftituent elements of, the materials fubmitted to fermenta- tion, we have (adds M. L.) next to examine the produfb refult- ing from that prccefs. For this purpofe, I placed the above 510 libs, of fermentable liquor in a' proper apparatus, by mean* of which I could accurately determine the quantity and quality of gas difengaged during the fermentation, aud could even weigh every one of the products feparately, at any period of the prccefs J judged proper^ An hour or two after the fubftances are mixed together, efpecially if they are kept in a temperature of from. 15° (65.75*) to 1 8° (72.5°) of the thermometer, the firft marks 6f fermentation commence ; the liquor turns thick and frothy, little globules of air are difengaged, which rife and burft at the furface ; the quantity of thefe globules quickly increafes, and there is a rapid and abundant production of very pure carbonic acid, accompanied with a fcum, which is the yea-ft feparating from the mixture. After fome days, lefs or more, according to- the •degree of Jieat, the inteftine motion and difengagement of gas di- roinim ; but thefe do not ceafe entirely, nor is the fermentation completed for a confiderable time. During the procefs, 35 libs. 5 OK. ^gros. iggrs, of dry carbonic acid are difengaged, which carry along with them 13 Jibs. 14 oz. 5 gros. of water. There re- mains in the veflel 460 libs. 1 1 oz. 6 grot. 53 grs. of vinous liquor, {lightly acidulous. This is at firft muddy, but clears of itfelf, and depofits a portion of yeaft. When we feparately anal yfe all thefe fubftances, which is effefted by very troublefome procefles, we hare the refults as given in the following tables, VOL. HI. F TABLE 66 Component Principles [Book VIII. of hydrogen, which forms water, by combining with the vital air of the atmofphere during combuftion. That it alfo contains a proportion of carbon, has been, proved by M. Berthollet, who found that when a mix- ture of ardent fpirit and water is burned, the refidual fluid precipitates lime water, which muft proceed from its containing fome carbonic aeid. Spirit of wine afllimes TABLE I V. Products of Fermentation, - 2$ 7 i 34 9 14 2 57 5 OK. 4 grcs. 19 T Qxypen >rs. of carbonic acid, j ch^coal .ompofed of £ 408 Afo. 15- 10059 5 4*7 'Oxygen, combined with hydrogen - 31 6 I 64 57 libs. 11 cz. I gros. 5% grs. of dry alko-«> hoi, compofed of Hydrogen, combin- ed with oxygen Hydrogen, combin- ed with charcoal 5 4 8 0 5 5 3 o Charcoal, combined with hydrogen - 16 ii 5 63 2 libs. 8 ex. of dry f Hydrogen 0 2 4 0 acetous acid, com- < Oxygen i II 4 0 pofed of £ Charcoal 0 10 0 0 4 libs, i oz. 4f.gr os. 3 f Hydrogen 0 5 i 67 grs. of refiduum of < Oxygen fugar, compofed of (_ Charcoal - 2 9 2 7 2 27 53 , lib. 6 c*. ogros. S f tt>'dr°Sen - - grs.of dry%ftUchargcoaI I compofed of 1 . O e 0 0 2 13 0 2 2 4l »4 3° 37 510 7/fo. Total - 510 o o « TABLE Chap. 6.] of drdent Spirit. 67 affumes the form of an elaftic fluid at the temperature of 185 degrees. Spirit TABLE V. Recapitulation of the Produfii* I' Water Carbonic acid - Alkohol Acetous acid Refiduum of fugar Yeaft C Carbonic acid 28 Ills. 12 oz. 5 gros, \Alkohol 59 grs- of charcoal,< Acetous acid contained in the J Refiduum of fugs-r f Yeaft Water Water of the alkohol - Combined with the charcoal of the alko. Acetous acid Reiiduum of fugar _ Yeaft, 2 grcs. 37 grs. of azote in the yeaft Total - 7 1 libs: 8 oz. 6 gros. 66 grs. of hydrogen, contained in the 5 1 o //'<£/ libs. oz. grcs gri 347 10 o 59 25 7 i i 34 31 6 i 04 i 1 1 4 ° 2 9 7 27 O »3 i 14 9 H 2 57 16 ii 5 63 0 iO 0 0 I 2 2 53 0 6 2 30 61 5 4 27 5 8 5 3 4 o r o o 2 4 o 0 5 1 67 0 2 2 4t 0 O 2 37 510 o ' In thefe refults, I have been exaft, even to grains ; not that it is poflible, in experiments of this nature, to carry our accuracy fo far; but as the experiments were made only with a few pounds of fugar, and as, for the fake of comparifon, I reduced the refults of the aftual experiments to the quintal or imaginary hundred pounds ; I thought it neceffary to leave the fractional parts precifely as produced by calculation. « When we confider the refults prefented by thefe tables with attention, it is eafy to difcover exafily what occurs during fer- mentation. In the firft place, out of the 100 libs, of fugar em- ployed, 4 Ills, i 02. 4 gros. 3 grs. remain, without having fuffered decompofition ; fo that, in reality, we have only operated upon 95 libs. 14 ox,. •} gros. 69 grs. of fugar ; that is to fay, upon 61 lib. 6 oz. 45 grs, of oxygen, 7 libs. 10 oz. 6 gros. 6 grs. of hydrogen, and 26 libs. 13 ex. r grot. 19 grs. of charcoal. By comparing F 2 thefe 6» Etber. [Book VIII. Spirit of wine and the acids act with confiderable violence on each other. When ftrong vitriolic acki is poured on an equal quantity of rectified fpiritof wine, a flrong heat, with a remarkable hiding noife, are ex- cited j the two fubflances become coloured, and emit a fweet fmell, refembling that of lemons, or the apple called golden rennet. If the mixture is made in a retort, and then fubmitted to diftillation in the well-- regulated heat of a fand bath, a large receiver, kept cool by the application of moiftened cloths, being adapted, the volatile products may be condenfed. Thefe are : i. Spirit of wine of a fweet fmell. 2. A thefe quantities, we find that they are fully fufficient for form- ing the whole of the alkohol, carbonic acid, and acetous acid pro- duced by- the fermentation. It is not, therefore, necefiary to fup- pofe that any water has been decompofcd during the- experiment, unlefs it is pretended that the oxygen and hydrogen exift in the fugar in that Hate. On the contrary, i have already made it evi- dent that hydrogen, cx\-gen, and charcoal, the three conftituent elements of vegetables, remain in a ftate of equilibrium or mutual union with each other, which fubiifts fo long as this union remains undifturbed by increafed temperature, or by fome new compound attraction ; and that then only thefe elements combine, two and t« o together, to form water and carbonic acid. ' The effefts of the vinous fermentatron uponfugar are thus re- duced to the mere feparation of its elements into two portion? ; one part is oxygenated at the expence of the other, fo as to form carbonic acid, \vhiii1 the other part, being difoxygenated in favour of the former, is converted into the combuflible fubitance alko- hol ; therefore, if it was poffible to re-unite alkohol and carbonic acid together, we ought to form fugar. It is evident th§£ the charcoal and hydrogen in the alkohol do not exitt in tire ftate of oil, they are combined with a portion of oxygen, ivhich renders ihcm mifcib'e with water ; wherefore thefe three fubftances, oxy- gen, hydrogen, and charcoal, exiil: here likewife, in a fpecies of equilibritfrn or reciprocal combination ; and in fadr, when they are rriade to pafs through a red hot tube of glafs or porcelain, this onion or equilibrium is deftroyed, the elements become combined two and wo, and water and carbonic acid are formed. fluid Chap. 6.] A-cdous Fermentation. 69 fluid called etber, extremely volatile, and alfo of a pleafant odour: this comes over as foon as the fluid in the retort begins to boil, and the upper part of the receiver is at the fame time covered with large diftinct dreams of the fluid, which run down its fides. 3. A light yellow oil, called iweet oil of wine j and 4, a fulphureous fpirit pafles over, the white colour and fmell of which indicate the proper time for changing the receiver, in order to have the ether feparate ; and this is fucceeded by. black and foul vitriolic acid. Ether is a fluid of a peculiar nature. It is the lighted and mofl volatile of all unelaftic fluids, and its tendency to afiume the elallic form is fo ftrong, that it is quickly diflipated in the ordinary heat of the at- mofphere, unlefs confined. It is highly inflammable, fo that it is dangerous to bring a candle near any con- fiderable quantity of it, the vapour taking fire, and Communicating the inflammation to the whole volume. The acids with which fpirit of wine is diftilled, in order to obtain ether, feem to effect this principally by rob- bing the fpirit of part of its carbon, which latter fub- ftance occafions the dark colour in the mixture, by decompofing the acid. A fmall part of the acid ad- heres to the ether in its afcent, and this conftitutes the differences which exift among the ethers, according to the. acid by which they were produced. The ACETOUS FERMENTATION is dill more fimple than the fpirituous, and confifts merely in the abforp- tion of the vital or oxygenous part of the atmofphere, by which vinous fluids are converted into vinegar, whence it appears that it is the proportion of oxygen alone which conftitutes the vaft difference that exifts between ardent fpirit and vinegar. That wine is con- verted into vinegar, by the addition of oxygen, is proved, as well from the general analogy of the for- F 3 mation yo Putrid Fermentation. [Book VIII, rnation of other acids, as by the following direct ex- periments. In the firft place, we cannot change wine into vinegar, without expofing the former to the con- tact of air containing oxygen, or employing fome other mode of oxygenation; fecondly, this procefs is accom- panied by a diminution of the volume of the air in which it is carried on, from the abforption of oxygen ; and thirdly, wine, by being converted into vinegar, is increafed in weight. The PUTRID FERMENTATION is the deftruction of the equilibrium which holds the conftituent principles of bodies in a ftate of combination. Thus a vegetable fubftance, which when entire confifts of a triple com- bination of hydrogen, oxygen, and carbon, is refolved by putrefaction into hydrogen gas, and carbonic acid gas, which confifts of oxygen and carbon. As there is not enough of oxygen to convert all the carbon into carbonic acid gas, a quantity of the charcoal remains behind, mixed with the earthy and faline matter con- tained in the vegetable. Thus putrefaction in a vege- table fubftance, is nothing more than a complete ana- lyfis of it, in which the conftituent elements aredifen- gaged in the form of gas, except the earth, and a quantity of charcoal which remains in the ftate of mould. Such is the refult of putrefaction when the fubftances fubmitted to it contain only oxygen, hydrogen, char- coal, and a little earth. Hut this cafe is rare; and thefe fubftances putrefy imperfectly, and with difficulty. It is otherwife with fubftances containing azote, which indeed exifts in all animal matters, and in a confider- able number of vegetables. The putrid ferment mon of animal fubftances is commonly called putrefaction, and this, is well known to take place in them, after they are deprived of life. The circumftances which favour putre- Chap. 6.] Putrefaftion. 71 putrefaction are the fame as thofe which promote the fpirituous and acetous fermentations, viz. humidity, the admiffion of air, and a due degree of heat. Heat to a certain degree promotes putrefaction, yet 20° above that of the human blood feems to prevent it. A fmall piece of fifh which was luminous, and confcquently putrid, was put into a thin glafs ball, and water of the heat of 1 1 §° extinguifhed its light, and confequently flopped its tendency to putrefa6tion, in lefs than half a minute ; on taking it out of the water, it began to re- cover its light in about ten feconds, but was never fo bright as before *. Azote, which abounds fo much in animal fub- ftances, not only occafions a more rapid putrefaction, but renders its products confiderably different from thofe afforded by the decay of fuch vegetables as do not contain azote. In the putrefaction of animal matters, the hydrogen, inflead of efcaping in a feparate date, combines with the azote, and forms volatile al- kali. The hydrogen gas alfo difTolves a part of the carbon, the fulphur, and the phofphorus, all which ilibflances enter into the compofuion of animal matter; with thefe, it forms compound aeriform fluids, which have obtained the following names, car- bonated hydrogen gas, fulphurated hydrogen gas, and phofphorated hydrogen gas. The two latter of thefe gaffes have a peculiar, difagreeable odour, and.> together with the volatile alkali, occafion the penetrating and' o^ffenfive exhalations which proceed from putrid mat- ters. Sometimes volatile alkali predominates j which affects the eyes; fometimes, as iri feculent matters, the fulphurated gas is moft prevalent; and fometimes, as in putrid herrings, the phofphorated 'hydrogen gas is * Prieflley's Hift. of Optics, p. 579. F 4 moft 72 Mujcular Matter changed Into Oil. [Book VI It. moft abundant. Carbonic acid gas is alfo difengaged. It appears highly probable, that water, which is fo neceffary to putrefaction, is decompofed during that procefs, and that its component principles, oxygen and hydrogen, contribute to the great quantity of gaffes which are produced. Oxygen feems alfo to be abforbed from the atmofphere, fince putrefaction is expedited by vital air. M. Fourcroy and M. Thouret have obferved fome peculiar phenomena in dead bodies, buried at a certain depth, and preferred to a certain degree from contact of air : having found the mufcular flefh converted into true animal fat. This muft have ariien from the difengagement of the azote by fome unknown caufe, leaving only the hydrogen and charcoal re- maining, which are the elements of fat or oil. This obfervation, M. Lavoifier remark?, may at fome future period lead to difcoveries of great importance to fociety, by enabling the chemift to convert into oil fubftances which confift of nearly the fame principles, but which are at prefent of no value. The decompofition of vegetable matters by fire, was noticed in treating of inflammable fubflances, in the chapter on carbon or the carbonaceous principle j and the mode of extracting from the afhes of certain plants that ufeful fubftance the fixed alkali, has been alfo defcribed. There is perhaps no procefs of nature better under- flood than that of fermentation, and yet there is not any more calculated to excite our aftonifhment ; there is not any inftance within my recollection fo ftriking, of the furprizing change which combination produces in bodies ; and it is the more wonderful, when we confider, that different proportions of the fame ingredients produce fluids efTentially diflinct in all their Chap. 6.] jftbeifm incwflftent with Philofophy. 73 their leading characters. He that " made a weight for the winds, and weigheth the waters by meafure j" how excellenrly has he ordered all things for the be- nefit of h;s creatures ! |{ The undevout aftronomer is mad," is the ftrong exprefTion of a fublime writer; yet* if the wifdom and providence of God is evi- dent in thofe immenfe bodies, of the ftructure of which we are in a great meafure ignorant, finely it is much more fo in thefe minute operations, which are the immediate objects of our fenfes, where every thing is plainly the effect of intelligence anddefign; and, however ignorant and fuperficial obfervers may wander from the path of truth; the naturalifl at lea# can never be an atieift. [ 74 3 [Book IX. BOOK IX, OF ANIMALS. CHAP, I. OP ANIMAL MATTER IN GENERAL. Qextral Remarks on Animal Bodies* — Products from the Dift illation cf Animal Matter. — Elementary Principles which enter into the Compojititn cf Animal Matter.— Animal Acids — Different Forms ef Animal Matter. — Jelly* — Glue.- — Lymph, — Further Products. — fat. — Fibrous Parts. IN treating of organized bodies, as introductory to an account of the vegetable fyftem, fome obferva- tions were made, which are alib in a great meafure ap- plicable to animal nature. The elementary principles, however, which enter into, the compofition of animal bodies are more numerous than thofe which are found in vegetable matter ; and at the fame time the ftruc- ture of animals is much more complex than that of plants. In both, the growth and increafe is provided for by a curious kind of chemical apparatus, adapted for effecting thofe wonderful changes, diilblutions, and combinations of matter, which are effential to their refpective natures. All, however, that we have been able to difcover in vegetables, is fome traces of a vafcular fyftem ; whereas, in animal nature, there is not only a mod elaborate fyftem of veflels, but means provided for the segmentation of the tem- perature, and for the fulfilling of thofe functions which belong Chap, i.] Complex StruHure of Animals. 75 belong to a creature, endued with a power of volun- tary motion, and of thought. To defcribe with accuracy the fpecific character- iftics of different animals, to enter into the detail of what is called comparative anatomy, would employ an immenfe and elaborate treadle -, and indeed to acquire the neceffary knowledge for fuch an under- taking would occupy a long life. As the object, however, of the prefent work is to give a general view of nature, rather than to enter into that rninute- nefs of difquifition which is chiefly neceffary for technical purpofes, or for thofe inquirers whofe leifure and patience far exceed thofe of the majority of man- kind, it will be neceffary to confine the prefent fub- ject within reafonabk limits. And fince it would be jmpoffible, in fuch a work, to treat of the fpecific or- ganization of every animal, I have made choice of that one, whofe parts and functions are found to be the moft perfect ; and as it is eafier to look down from an eminence than to afcend the heights of cre- ation, from what will be ftated in the fucceeding pages on the economy of the human body, it will not be a matter of great difficulty to comprehend that of other animals *. The plan which will be pur- fued in this part of the work, will not: be materially different from that which has been adopted in the preceding. After a few obfervations on the com- ponent principles of animal matter, 1 fhall proceed to confider the ftructure of thofe organs which con- ftitute the animal machine ; and laftly, the functions to which thofe organs are fubfervient. * The moft ft: iking and charafteriftic differences in the fabric of different animah are however noticed; but to defcribe minutely the natural economy of ever/ diftindl race of animals, would require an immenle treadfe, and indeed has never }*et been done. When g6 Animal Mailer. [Book IX. When animal matter is diftilled with a ftrong heat, we obtain a watery fluid, holding in folution fome fal ammoniac, fuperfaturated with volatile alkali ; a light oil, and a ponderous dark oil, mixed with concrete volatile alkali ; a fpongy coal remains in the retort, of difficult incineration, and which contains fea-falt, mild fofille alkali, iron, and calcareous earth, combined with phofphoric acid. Such are the products afforded by the diftillation of all animal matters, except that the proportions vary, according to the degree of folidity in the part fubmitted to diftillation. The moft characleriftic mark of ani- mal matter, is its containing azote, which confiderably alters its products, both by putrefaction and diftillation, and which in both thefe precedes combining with hydrogen produces volatile alkali. As vegetables and animals, however, pafs by infenfible degrees into each other, fo there are fome vegetables which afford vola- tile alkali, and which confequently contain azote ; Chough in far leis quantity than any animal matter. The elementary matters which enter into the com- pofidon of the foft part.s of animals, are carbon, hy- drogen, azote and oxygenj the bones are compofed erf" calcareous earth and phofphoric acid: a very fmall quantity alfo of iron, and of fome neutral falts, particularly fuch'as are compofed of the mine- nil and volatile alkalies, and lime, combined with the muriatic, phofphoric and carbonic acids, are dil- covered by careful analyfis. By the application of hear, the elementary matters above mentioned afTume pew arrangements and combinations ; hydrogen and oxygen uniting, form water; hydrogen and carbon, cil ; hydrogen and azote, volatile alkali ; oxygen and carbon, cretaceous or carbonic acid: Ibme of the gaffes alfo efcape in a feparate Mate, and part of the carbon remains Chap. I.] Analyfis of Volatile Animal Oil. 77 remains behind with the earthy matter. Lavoifier, after having treated of the decompofition of vegetable matter, obferves: < Animal fubftances, being compofed nearly of the fame elements with cruciferous plants, give the fame produces in diilillation, with this difference, that,/ as they contain a greater quantity of hydrogen and azote, they produce more oil and more ammoniac. I^fhall only produce one fact, as a proof of the exactnefs with which this theory explains all the phenomena which occur during the diftillation of animal lub- itances — which is the rectification and total decom- pofition of volatile animal oil, commonly known by the name of Dippel's oil. When thefe oils are procured by a firft diftillation in a naked fire, they are brown, from containing a little charcoal almoft in a free ftate ; but they become quite colourlefs by recti- fication. Even in this ftate the charcoal in their com- pofition has fo flight a connection with the other ele- ments, as to feparate by mere expofure to the air. If we put a quantity of this animal oil, well rectified, and conicquently clear, limpid, and tranfparent, into a bell-glafs filled with oxygen gas over mercury, in a fhort time the gas is much diminilhed, being abforbed by the oil ; the oxygen, combining with the hydrogen of the oiJ, forms water, which finks to the bottom ; at the fame time the charcoal which was combined with the hydrogen being fet free, manifefts itfelf by ren- dering the oil black. Hence the only way of preferr- ing thefe oils colourlefs and tranfparent, is by keeping, them in bottles perfectly full, and accurately corked, to hinder the contact of air, which always difcolours them. c SuccefTive rectifications of this oil furnilh another phenomenon confirming our theory. IG each diftil- lation ^S Animal Acids* [Book IX; lation a fmall quantity of charcoal remains in the retort^ and a little water is formed by the union of the oxygen contained in the air of the diftiping veflels with the' hydrogen of the oil. As this takes place in each fuc-« ceftlve diftillation, if we make ufe of large veffels, and a confide rable degree of heat> we at lall decompofe the whole of the oil> and change it entirely into 'water and charcoal. When we ufe fmail vdlelsj and efpe- cially when we employ a flow fire, or a degree of heat little above that of boiling water, the total decompo- lition of thefe oils, by repeated diftillatiorij is greatly •lore tedious, and more difficultly accomplimed/ Animal matters are compound falifiable bafes brought to the (late of oxyds by combination with oxygen, and which, by the further addition of that prin- ciple, are capable of becoming acids. Several animal acids have been difcovered, fome of which approach very near to the vegetable acids. Their bafes have not been afcertained with accuracy, but are fuppofed to be different combinations of carbon, hydrogen, and azote. The animal acids at prefent known, are the following : Lactic acid, obtained from milk. Saccho-laclic, from fugar of milk. Formic, from ants. Bombic, from filk-worms. Sebacic, from fuet. Lithic, from urmary calculus. Pru'ffic, extracted from blood, or other animal matter, by means of fixed alkali ignite .' with thefe matters. Having mentioned the principles afforded by the complete decomposition of animal matter, it will be proper to notice certain matters into which the foft parts of animals may be refolvcd by the action of menurua. Chap, i.] Jelly, Glue, &V.. 79 menftrua. If a part of an animal is boiled in water, it is gradually diffolved, and a matter is extracted, which forms a fjiid but tremulous mafs when cold, and which is called jelly. This is found moft plentifully in the white parts of animals, but may be obtained in a fmaller or greater proportion from all. It is nearly inodorous and infipid, and is foluble both in cold and hot water, but more eafily in the latter. When its watery parts are more fully evaporated, it forms glue. The jelly of animals is very analogous to the gum of vegetables, except that the latter does not contain azote, and of courfe is lefs prone to the putrefaclive fermentation, and is incapable of affording volatile al- kali. The glue obtained by boiling animal matters, differs in fome meafure according to the firmnefs or laxity of the fubftance from which it is obtained ; thus the fkins, tendons, cartilages, and ligaments afford the firmed glue. The fkins of eels are the bafis of gold iize ; and from old white leather gloves and parch- ment is made a kind of glue ufed by painters. Glues differ from each other in their confidence, tafte, fmell, and folubility : there are fome which readily become foft in cold water; others are not difiblved but in boil- ing water -, but the preparation of the latter is not ge- nerally known. The beft glue is tranfparent, of a yel- low brownifh colour, without fmell and tafte, and en- tirely foluble in water, with which it forms a vifcid uni- form fluid. Animal jelly differs from glue, only in poffeffing a lefs degree of confidence and vifcidity. The firft is more efpecially obtained from the foft and white parts of animals, and is far more abundant in thofe which are young. Glue is obtained in greateft perfection from the toughed parts of older animals. Jelly and glue are infoluble in fpirit of wine. Lymph So Fat> Fibrous Matter, fcte [Book IX. Lymph or ferum conftitutes the greater part of the fluids of animals, and will be afterwards treated of as a conftituent part of the blood. Spirit of wine, when applied to animal matters, dif- folves an extractive- fubftance, which is depofited on the evaporation of tl>e fluid ; this matter is alfo foluble in water. It fwells and liquifies by heat, and emits a fmell fomewhat refembling that of burned fugar ; it is chiefly this fubftance which covers the furface of roafted meat, in the form of a brown cruft. The fit of animals approaches very nearly to the nature of the fat oils of vegetables. The globules which rife to the furface of water in which meat is boiled, confift of the fat. The fat of animals, as well as the fat oils of vegetables, affords a peculiar acid, which is calle.d the febacic acid, or acid of fuet. After all thefe matters are extracted, there remains nothing but a white fibrous matter, infipid, and infolu- tie in water. This matter has all the characters of the fibrous part of the blood, which I mail treat of in the following chapter. Chap. 2.] [ 8i ] CHAP. It. OF THE BLOOD. Sanguineous 'and exfanguineous Animals. — Warm and co !J Hooded Ani* mah.—Semm and Craffamentum. — Polypufes. — Analyfis of Blood.— • Lymph.— Iron in the Blood. — Caufe of the Red Colour.— Red Glo- &uIes.~—Htirivfon's Experiments. TPIIS fluid, which is fo efier.tial to life, varies confiderably in different fpecies of animals. Iri man, and other large animals, it is of a red colour, but in fome fmaller animals the circulating fluid is nearly colourlefs, and therefore fuch animals are called exfanguineous ; though with little propriety, as their circulating fluid appears to anfwer all the purpofes of blood, and there feems no reafon to affirm that nothing can be blood, which is not of a red colour; The molt remarkable difference in the blood of animals, is with, refpeft to the temperature. The blood of man, qua- drupeds, and birds, is hotter than the medium they inhabit^ they are therefore called animals with warm blood. In fiflies and reptiles it is nearly of the temperature of the medium they inhabit ; and thefe are therefore called animals with cold blood. The temperature of the blood, as well as the change of co- lour to a brighter red, which the blood undergoes in pafling through the lungs, will be treated of in a future chapter on refpiration. When blood is firft drawn from a vein, it appears to be an homogeneous red fluid : it then confolidates into one uniform mafs ; in a little time a yellowifh watery liquor begins to feparate fronj it, which is more VOL. III. G or 82 Compofition of the Blood. [Book IX." or lefs in quantity, according to the date of the blood; the red mafs, in the mean time, contracts greatly, in its dimenfions, expelling the watery liquor from its pores, and confequently increafing in firmnefs and denfity. This reparation happens in the body after death, and produces thofe concretions in the heart, and large vef- iels, thofe adheiive mafTes called polypufes, which were formerly fuppofecV to have exifted during life, and fome times to have been the immediate cccafion of death. By agitation, blood continues fluid ; but a con- fident fibrous matter adheres to the flick «or inftrument made ufe of to ftir it, which by repeated ablution in water becomes white, and appears to be very fimilar to the fibres of animals obtained by wafhing away the other adhering matters. Received from- the vein in warm water, blood depofits a quantity of tranfparent filamentous matter, the red portion continuing diffolved in the water. On evaporating the fluid, a red fub- ftance in the form of powder, or eafily reducible to it, is left. Blood infpiflated- to drynefs leaves a dark co- loured mafs, amounting at a medium to about one fourth part of its weight, of a bitter faline tafte, eafily inflammable, and burning with a blueifh flame. The exficcated blood is not foluble in acid or alkaline li- quors, but gives fome tinge to water and to fpirits of wine ; and is more powerfully acted on by dulcified fpirit of nitre. Recent blood is coagulated by the mineral acids, and by moft of the combinations of them with earthy and metallic bodies. With vegetable acids, and with foiutions of neutral falts, it mingles equally without coagulation. Alkalies, both fixed and - volatile, render it more fluid, and preferve it from coagulating. Blood by ciiftiliation affords the fame refults as other animal matters. Six pounds of human blood diftiiled to drynefs, with a gentle heat, were re- duced Chap. 2.] Lymph or Serum. 83 duced to a pound and an half 5 after which the mafr, was urged with a graduated fire, till the retort at laft became red hot* The produce was feventeen ounces of liquor, twelve of which were a red and very empy- feumatic volatile and alkaline fluid, and the other' five Were oil. What remained in the retort was a light Coal, weighing four ounces and a half. It has been already mentioned that blood fponta- neoufly feparates into two parts, a coherent mafs called the craffamenturri, and an aqueous liquor called the ierum, with which the crafTamentum is furrounded. Lymph or ferum, which is alfo called the albumi- nous matter, from its coagulating into a white mafs by the application of a heat equal to 1 56 degrees of Faren- heit/s thermometer, is very analogous td the white of egg. Serum is alfo coagulated by acids and by ardent fpirit ; alkalies render it more fluid. It converts fyrup of violets to a green. Its colour is yellowilh, inclining to green j its tafte is faline, and it feels between the fingers in fome degree un<5tuous and adbefive. By diftillation it affords the fame principles as animal matters in generah Serum, expofed to a warm temperature in the open air paffes quickly to putrefaction. It unites with water in all proportions, but they are kept feparate by their different denfities, unlefs agitated together* Serum poured into boiling water for the moil part coagulates inftantly. The coagulation formed in ferum by the addition of an acid, diffolves very quickly in volatile alkali, which is the true folvent of the albuminous part ; but it is not at all foluble in pure Water. The coagulation formed by fpirit of wine, on the contrary, is foiuble in water, as M. Bucquet has difcovered. This liquid, M. Fourcroy concludes, is an animal mucilage, compofed of water, acidifiable oily bafes, G 2 marine 84 Iron contained in Blood. [Book IX. marine fait, chalk of foda, and calcareous phofphat ; thi^ laft appears to produce the rofe-coloured precipi- tate, obtained by pouring the nitrous folution of mer- cury into ferum. Though the liquid is fcarcely co- loured, the addition of nitrous acid, and more efpeci- ally of mercurial nitre, produces a rofe or light fiefh- colour, which M. Fourcroy has often obferved in many other animal liquors. The crailamentum, when well warned in water, is feparated into two very dillinct fubftances, one of which is diflblved, and tinges the water of a red co- lour, while the other remains behind in the ftate of a white fibrous matter, the fame as that which adheres to the ftirrer with which recent blood has been agitated, in order to prevent its coagulation. The water in which the red part is diflblved, when heated with different menflrua, exhibits all the characters, of ferum ; but it contains a much greater quantity of iron, which may be obtained by the incineration of the coal, and fubfequcnt warning to feparate the faline matters. The refidue of this wafliing is a yellow calx of iron, of a beautiful colour, and ufually attracted by the magnet. The red colour of the blood is therefore with fome appearance of reafon attributed to this metal. Iron has been obtained from the blood in confiderable quantity by Menghini, Rpueile, and Bucquet. The lame chemifts found that iron was capable of pa fling into the blood from the inteftines, fince patients \vho were under a courfe of martial medicines are known todifcharge a part of it by the urinary paflages. Iron is obtained from the red particles of the blood, but not from the warned eoagulum. Thefe facts, to- gether with the increafed rednefs of the blood by palling through the lungs, where it may be fuppofed to iiifrcr a degree of calcination from the abibrption of Chap. 2.] Micro/copied Appearance of the Blood. 85 of oxygen, render the above opinion highly pro- bable. The fibrous part of the blood, when thoroughly warned, is white and infipid ; by diftillation, like other animal matters, it affords water, oil and volatile alkali. Expofed to a gentle heat, it is much hardened ; when fuddenly expofed to a ftrong heat, it Iririnks up like parchment. It putrefies very rapidly, and affords much volatile alkali. It is infoluble in water, and when boiled in that fluid hardens, and afiumes a grey colour. Acids unite with it, and in particular the nitrous acid difiblves it, and extricates azote and nitrous air; while the refidue by evaporation affords acid of fugar in cryf- tals, a peculiar oil in flocks, and the phofphoric fait of lime. Marine acid forms a green jelly with the fibrous part of the blood. The acid of vinegar diffolves, it with the affiftance of heat ; water, and more parti- cularly alkalis, precipitate the fibrous matter when dif- folved in acids. The animal fubftance is decompofed in thefe combinations ; and when feparated from the acids by any method, it no longer retains its former properties. The microfcopical appearances of the blood have attracted great attention. Various accounts have been publimed on this fubjeft, mod of which feem to have been framed more on theory and pre-conceived opi- nion, than actual obfervation. Thefe falfities have been detected by Mr. Hewfon, whofe microfcopical experiments on the blood are the lateft which have been made, and remain at prefent (as far as relates to the compofition of the blood) uncontradicted. I ihall therefore tranfcribe the following particular account of them, given by himfelf in a letter to Dr. Haygarth, phyfician, in C heller. G 3 86 Mifrofcopical Appear am es of Blood. [Book IX. c The red particles of the blood, improperly calle4 globules, are flat in all animals, and of very different fizes in different animals. In man they are fmall, as fiat as a milling, and appear to have a dark fpot in the middle. In order to fee them diftinctly, I dilute the blood with frefti ferum. My predeceffors, not having thought of this, could not fee them diftinctly. And Lewenhoeck in particular, imagining a round figure finteft for motion, concluded they muft be round in the human body ; though he and others allowed that in frogs, &c. where they viewed them diftinctly, from the blood being thinner, they were flat. Now I prove that they are flat in all animals. In the human blood, where thefe particles are fmall, it is difficult to deter- mine what that black fppn is, which appears in the center of each. Some hate concluded that it was a perforation ; but in a frog, where it is fix times as large as in a man, it is eafy to (hew that it is not a perforation, but on the contrary, is a little folid, which is contained in the middle of a veficle. Inftead, there- fore, of calling this part of the blood r&& globules, I fhould call it red veficles ; for each particle is a flat ve- ficle, with a little folid fphere in the center. f I find that the blood of all animals contains veficles of this fort. In human blood there are millions of them, and they give it the red colour j but in infects they are white, and lefs numerous in proportion than in man and quadrupeds. As they are flat in ail ani- mals, I fufpect that ftiape is a circumftance of im- portance, but can be altered by a mixture with differ- ent fluids. And I find, that it is by a determinate quantity of neutral fait contained in the ferum, that this fluid is adapted to preferving thefe veficles in their flat fhape: for if they are mixed with water, they become found, and diffolve perfectly •, but add a little of any neutral Chap. 2.] Red Vefides in the Blood. 87 neutral fait to the water, and they remain in it without any alteration in their ihape, and without difiblving. ' Now, when it is considered that the blood of all animals is filled with thefe particles, we muft believe that they ferve fome very important purpofe in the animal ceconomy ; and fince they are fo complicated in their ftrufture, it is improbable that they fhould be formed by mechanical agitation in the lungs or blood -veffels, as has been fufpected, but probably have fome organs fet apart for their formation. This I fhall endeavour to prove, when I have explained their ftructure a little more particularly, and men- tioned the manner in which I exhibit it. I take the blood of a toad or frog, in which they are very large ; I mix it with the ferum of human blood to dilute it; I find them appear all flat, fo they do in the blood- vefiels of this animal, as I have diftinctly feen in the web between its toes, whilft the animal was alive, and fixed in the microfcope. Their appearance in thefe animals is not unlike flices of cucumber. I next mix a little of the blood with water, which immedi- ately makes them all round, and then begins to diflblve them whilft they are round. I incline the ftage of the microfcope, fo as to make them roll down it; and then \ can diftinctly fee the folid in the middle fall from fide to fide, like a pea in a bladder. A neutral fait added to them at this time brings them back to their flat fhape ; but if the fait is not added, the water gradually diflblves away the veficle, and then the little fphere is left naked. Such is the compofition of thefe particles. I have exhibited thefe experiments to a confiderable number of my acquaintance, who all agree in their being fatisfadory. c The microfcope I ufe is a fingle lens, and there- fore as little likely to deceive us as a pair of ipectacles, G 4 88 Solid Particles in the Blood. [Book IX, which, as is allowed by all who ufe them, do not dif- figure objects, but only reprefent them larger/ It is unneceflary to follow Mr. Hewfon into his fpeculations with regard to the ufe of the thymus and lymphatic glands, which he thinks are defigned to fa- bricate the middle folid particles of the blood which are afterwards to be%furnifhed with veficles in the cells of 'the fpleen. Thefe inquiries may fhew the inge- nuity of their author, but will not anfwer our purpofe, which is to detail with concifenefs what has been afcep- tained with certainty. Chap. 3.] [ 89 ] CHAP. III. STRUCTURE OF ANIMALS. Sixe of Man.— His ereft Pofture. — Varieties In ike Strufiure of Aiii- ma/s.— Parts of the Animal Body* IN taking a general view of the formation of MAN, a circumilance of importance is his fize, confidered in relation to the force of gravitation. If the fize of man was much greater than it is, fuppofmg his ftrength to be only in proportion, his motions would be much flower, and more laborious ; nor would his increafe of fize be entirely compenfated by a diminution in the force of gravitation, for this would expofe him to in- conveniences, on account of the various relations in which he ftands to other objects. On the contrary, was man much fmaller, though he would gain in celerity what he would lofe in force, yet his weaknefs would incapacitate him for acting with advantage on confiderable mafTes of matter. On the whole, if mould' feem, that neither an increafe of fize with an increafe of gravitation •, nor a diminution of fize with a diminution of gravitation ; nor an increafe of eicher with a diminution of the other, would in general fo well fuit, the conveniences of man, and his relation to other beings, as the Hate in which he at prefent fubfifts. The mod ftriking difference of ftructure between man and the other animals is his ere 61 figure, excel- lently adapted to the more extenfive views which he ' was 90 Aljurdities of Modern ' Metapbyjics. [Book IX. v/as defigned to take of nature -, and which, inftead of being a mark, as a French writer pretends to think, of human arrogance, in departing from the horizontal poilure, which was allotted to man in common with other quadrupeds, is one proof of the diftance which the Deity meant to interpofe between him and the reft of the animal creation. That author,, however, de- nies the fuperiority of man in every refpect; and main- tains, that the mental acquirements of a horfe would not be inferior to thofe of a man, if the former was furnilhed with fingers, and endued with the fame exqui- fite fenfe of feeling which the latter enjoys. We may grant that all our fimple ideas are derived from the in- formation of our fenfes -, but we would aik what experi- ments this philofopher or his adherents have made, to afcertain, that there can be no differences in the ftruc- ture of intellectual organs ? and upon what authority they conclude, that all the varieties we obferve in mental endowments, among individuals of the lame race, as well as among different races of animals, are folely to be referred to differences in the organs of fenfe ? But granting all that he requefts, how came man to have fingers and horfes none, if they were equally clefigned to gallop through the forell ? — he muft either have made fingers for himfelf, or he mufi have been originally -defigned by his Maker for nobler, occupations. The ftru&ure of man, moreover, in feveral other par- ticulars, entirely confutes the aflerdons of this contemp- tible vifionary ; but without attending to other circum- ftances, it will be fufficient to mention the formation of the lower extremities in man, fo different from the hind legs of quadrupeds, and fo admirably adapted to the erect pofture. By fome naturalifts the Ourang- Outang is confidered as the original flock of the human race. Chap. 3.] Structure of the Ourang-Outang. 91 race. His claims to humanity are founded upon his being able to walk upright, being furnifhed with fuch mufcles as are requifite for that purpofe. The form of his heart, lungs, bread, brains, and inteftines are iimilar to thofe t)f a man. He can fit upright with eafe, and can handle a flick with dexterity. That his race is diftinct, however, from that of man, is evi- dent from his having thirteen ribs on each fide, where- as man has but twelve. He has not the faculty of ipeech, and articulation is impofiible to him, on ac- count of the ftructure of the parts about the larynx. While, however, we diffent from thefe authors, in finking man to the level of other animals, let us re- flecl that the purpofe of nature feems to be, to diffufe life and enjoyment wherever they can exifl ; and let .us avoid the oppofite, narrow-minded, and, if pofiible, ftill more abfurd notion, that the happinefs of man is the fole object of creation. Jn the animals which more commonly fall under our obfervation, the furface is foft, and the bones are deeply feated ; but in others the reverfe happens, and we ob- ferve the bones forming a cafe to the fofter parts. We fee fome animals furniihed with wings, to fport in the regions of the atmofphere j fome immerfed by means of a heavy fhell, during the whole of their exiflence, in the depths of the ocean j and others furnifhed with organs, to perforate their dark paflage through the bowels of the earth. In general the bones of animals • are filled with marrow, but in many kinds of birds they are excavated for the reception of air, fitting them for floating more eafily on the furface of water, and at the fame time, when neceffity requires, for remaining longer beneath its furface. In fome animals, even the brain and heart efcape our moft careful refearches ; and fome, like vegetables, may be mukiplied from the 92 Parts of the Body. [Book IX. the limbs of their parents. So endlefs indeed are thefe differences, that there is perhaps no one circumftance of ftructure or function common to all animals. • But let us return from thefe extenfive profpects to the confideration of the ftructure of our own fpecies. Before we proceed, however, to confider the ftruc- ture of the body, it will be proper to premife a few very brief definitions' of the moft remarkable parts of which it confifts. Bones are hard fubftances, which form the bafis of the body. Cartilages are firm, fmooth, elaftic bodies, which cover the ends of the bones. Mufcles are contractile organs, which are attached to bones, and perform the motions of the body. Tendons are tough cords, by means of which mufcles are attached to bones. Ligaments are ftrong fibres or membranes, which connect bones to each other. Blood- veffels are membranous flexible tubes, which convey the blood to and from the heart. Lymphatics are tranfparent tubes, which perform abforption. Nerves are white cords connected with the brain, and are die inftruments of fenfation and voluntary mo- tion. Glands are organic mafles, deftined for die purpofe of fecretion. Chap. 4.] t 93 I CHAP. IV. x STRUCTURE OF THE BONES. Bones con/i/} of Fibres ; cellular. — The Marrow. — Wafte of Bone In old Age. — Kpipbjfes.'—PerioJleum, — Progrefs of Oj/ificatioK.— Articulation. TH E body, as Hippocrates long ago remarked, is a circle ; and therefore at whatever poinc "we were to begin the defcription, wefhould ultimately be equally led, by the connexion of parts, to the confi- deration of the whole. Since the bones, however, may be confidered as the bafis of the body, on which the other parts depend for fituation and fupport, it appears moil eligible in the firft place to confider their ftrufture and ufes. The bones con fift of fibres, distributed in lamella or plates ; thefe plates are not clofely applied to each other, but, with the intervention of tranfverfe fibres, conftitute cells. The cells are diflributed through the fubftance of all the bones, but are uniformly moft re- markable in the center, and on the fur face of the harder bones are fo fmall as not to be diftinctly perceptible without the aid of glafies. The marrow which fills the cavities of the bones is a fat oily fubftance, contained in a fine and tranfparent membrane, which receives numerous blood-veffels, and is fupporteci by the filaments of the reticuiar fub- ftance of the bones. If the different parts of a bone are pbferved, it is found that where the diameter of the bone is the leaft, there the fides arc thickeft and moft compadj where the diameter is greateft, which 94 Vhe Marrcw. [Book fX; •which is in general towards the ends of the long bones,- their ftrufture is very cavernous throughout. The marrow pervades the whole fubfbnee of the bones, but is moft remarkable in the middle part of the cavities of the long bones. Its appearance and nature alfo differ in different bones, or in the ^ame bone in the progrefs of life. Thus the marrow is bloody in chij- dren, oily in adults, and thinner and more watery in aged people. At the time of birth, the bones are very imperfect, particularly thofe of the head 5 fo that by being move- able in this part, and folding over each other during the time of delivery, an eafier pafiage is procured for the infant. There are many, projections from the bones, which in infancy are foft, but which in the adult ftate are bony j and the fame tendency to the for- mation of bone increafing with our years, bones which were feparate in the prime of life concrete in old age. In the decay of the body, however, the bones are di- minimed with the other parts, fo as in extreme old age to weigh a third lefs than in the middle periods of life. To far the greater number of bones whofe ends are not joined to other bones by immoveable articulation, are annexed, by the intervention of cartilage, fmaller bones, called epiphyfes or appendages. Iii young fub- jects thefe are eafily feparable, but in adults the point of conjunction is not very perceptible. The bones are furnifhed with a tough membrane, called the periofteum, which is fpread on their furface, and the principal ufe of which fcems to be to convey blood-refiels for their nourifhment ; thefe blood-vefiels are very numerous and remarkable in the bones in the infant liate, but become gradually lefs fo in the progrefs of life. It Chap. 4.] Perioftaim, &c. g$ It has been fuppofed that the bones were formed by the fuqceffive offification of layers of the penofteum. This opinion, however^ is contrary to what is obferved on examining bones in the progrefs of their formation : and is alib difproved by fome experiments, in which animals were fed with madder. . Their bones were found to be tinged in proportion to the le-ngth of time that they v/ere kept on this food ; but neither the pe- nofteum nor the cartilages were altered from their na- tural colour. The moil general divifion of the bones is that into the long and cylindrical, and the flat and the broad. The offification in both thefe kinds of bones begins in the middle, at feveral points at a time, and gradually extends towards the ends of the long bones and the cir- cumference of the broad. The ends of the long bones, where they are united to each other, are larger than their middle part, and ieveral advantages attend this ftructure. By thele. means the furface of contact between the two bones of an articulation is . increafed, their conjunction conic- quently becomes firmer, there is more fpace for the connection of mufcles, which alfo act more powerfully from their axes being further removed from the mid- dle of the joint, or the center of motion. The bones are united to each other, either moveably or immoveably. They are moveably articulated in three ways : — ift. By a ball and focket, which admits of motion in all directions, as in the fhoulder. sdly, By a hinge, which allows motion in only two directions, as in the knee ; and jdly, By a long procefs of one bone received into the cavity of another, which admits of a rotatory motion, as in the articulation of the firft and fecond vertebra of the neck. The immoveable articulation of bones is of two kinds : ift, where nu- merous 96 Articulation of Bones. [Book IX» merous procefles of two bones, like the teeth of faws, are mutually received into each other, as in the bones of the head; and 2dly, by the growing together of bones with the intervention of cartilage, as in the union of the os facrum with the ofla innominata. The ends of bones which move on each other are tipped with fmooth cartilage ; and the friction is flill further diminifhed by a fluid, much more flippery than oil itfelf, which is called the fynovia. The moveable joints are alfo furnifhed with ftrong membranes, called ligaments, which pafs from one bone to another, afford- ing ftrength, and retaining the heads of the bones in their cavities. For the purpofes of articulation, and the connection of mufcles, bones are uneven on their furface, and have numerous elevations and depref- fions. Chap. 5 CHAP, V. DIVISION OF THE SKELETON, WITH THE BONES OF THE HEAD. *The Skeleton briefly defcribed. — Bones of the CraniuiH.— Bones of the Face— of the Nofe — of the Palate. — The Upper and Under y#re unequal, for the grmer adhefion of the ftrong cir- cular Chap. 5.] Ethmoid Bout. roi cular ligament which pafles from the circumference of the foramen to the firft vertebra. On the in fide of the occipital bone 'are feveral ridges and furrows ; to one of the ridges is fixed the pofterior part ofthefalx, and the furrows receive the finufes which run in this part of the cranium. The ridges of this bone form a crofs, and round the middle of the crofs there are four large depreffions, feparated by its limbs j the two up- per depreflions being formed by the pofterior part of the brain, and the two lower by the cerebellum. The inner furface of the cuneiform procefs is hollowed for the reception of the medulla oblongata and the bafilar artery. Befides the great foramen, there are feveral other perforations in this bone, or between it and the adjoining bones, for the paJTage of nerves and blood- vefiels. The occipital bone at its tipper part, where it is chiefly expofed to injury, is very thick and ftrong, but lower down, where it is protected by the ftrong and thick mufcles which are inferted into it, it is often very thin. The occipital bone is connected above to the ofTa parietalia by the lambdoidal future ; laterally to the temporal bones by a continuation of the fame fu- ture ; below it is firmly connefted by an union of fub- ftance to the fphenoid bone, by means of the cuneiform proct-fs. The os ethmoides, or fieve-like bone, derives its name from the numerous fmall apertures with which it is pierced at its fore part. From the middle of the internal fide of the lamella, which is fo full of holes, a thick procefs rifes upwards j and being higheft at the fore part, gradually becomes lower as it is extended backwards. From a fancied refemblance of this pro- cefs to a cock's comb, it has been called the crifta- galli. The falx is connected to its ridge, and to the unperforated part of the cribrfcrm plate. All the pro- H 3 minences. 101 Sphenoid Bens. [Book IX. rfiinences, cavities, and meanders of the ethmoid bone are covered with a continuation of the membrane of the noftrils. The ufes of this bone are to fuftain the anterior lobes of the brain ; to give paffage to the ol- factory nerves, and attachment to the falx ; to enlarge the organ of fmelling, by allowing the membrane of the nofe a greater extent j to form a part of the orbit of the eyes, and the feptum varium. The os fphenoides, or wedge-like bone, which is fo called from its fituation in the middle of the bones of the cranium and face, is of a very irregular figure, and bears fome refemblance to a bat, with its wings ex- tended. This bone is generally divided into a body, and two fides or wings. When we view the external part of the os fphenoides, two or three remarkable pro- ceffes from each fide of it may be obferved, which are all of them again fubdivided. The firft piir confifts of the two large lateral proceffes or wings ; the upper part of each of which is called the temporal procels, becaufe they join with the temporal bones in forming the temples : that part of the wings which projects to- wards ihe infide, fomewhat lower lhan the temporal proceffes, and is fmooth and hollowed, forms part of the orbits. The loweft and back part of each wing runs out with a iharp point, called the fpinous procefs, to meet the point of the pars petrofa of the temporal bone. The fecond pair of external proceffes of the fphenoid bone are the aliform or pterygoid, and which ftand out almoft perpendicular to the bafe of the fkull. Each of them has two plates and a middle foffaat the pofterior furface. Of thefe plates, the exterior is the -broadeftj the interior are longed, and terminate in a hook-like procefs. Another pair of proceffes may be mentioned, viz. the little triangular thin proceffes which come from each fide of the fphenoid bone, where the pterygoid Chap. 5.] Sella ^urcica^ £f? the internal is thinner, more uneven, more brittle, and is lined with a thick vafcuhr membrane, called the dura mater. The bones of the head are united to each other by a number of tooth-like procefTes ; and thefe joinings are called futures. The coronal future runs acrofs the head, and connects the frontal bone to the parietal bones. The fagittal future divides the upper part of the head into two equal parts. It connects the two parietal bones to each other, and pafles from the mid- dle of the frontal to the middle of the occipital bone. The lambdoid future is interpofed between the back and fore parts of the cranium, or between the occi- pital and two parietal bones. The two fquamofe futures connect the temporal bones to the parietal. There are alib many lefs remarkable futures, which join the bones of the face to thofc of the cranium. Chap. 6.] [ 107 ] CHAP. VI. THE TEETH. General Defcription --.f the Teeth. — Incifores. — Canlai. — Mola.res.-~, Enamel of the Teeth.— Growth of the Teeth. — The Face lengthened offer Eight Tears cf Age. — Varieties in the Teeth of different Ani- mals. r~I~^ H E teeth, both of the upper and lower jaw, JL are fixed in Tuckets of the jaw-bones, formed of thin bony lamellas. That part of the teeth which pro- jefls beyond the gums, is called their body ; the exter- nal termination of the body, the corona or crown j and that which is hid, and which terminates in a wedge- like point, is called the radix or root. The roots of the teeth are perforated at their extremities, for the re-r ception of nerves and blood-vefTels. The teeth are divided into three orders. The four front cutting teeth, are called incifores. Next to thefe is placed on each fide a tooth, called from its form the canine or dog-tooth ; and lalily, on each fide five mo- lares or grinding teeth. The lad tooth on each fide, from its not being cut till after the age of puberty, is alfo called dens fapientias, or the tooth of wifdom. The four incifores are fmalier and narrower in the lower than in the upper jaw. The corona of the incifores is broad and fliarp, and in children is much notched* The roots of the incifores are (hort, and terminate in a fingle blunt apex. The canine teeth are ftronger, more acute, and more deeply rooted than the incifores. They are convex before and concave behind, and are fitted for tearing our food to pieces. The molares, by the eminences on the corona, and by their broad upper furfacesj are evidently, as their name expreffes, de- figned loS Sub/lance of tie Teeth. [Book IX. figned for the grinding of the food. The anterior molares are fmaller and lefs uneven on the corona than the pofterior; the ftrongeft being placed neareft the articulation of the jaw bone, becaufe there we can exert the greateft force. The roots of the molares are long and pointed ; each tooth has two, three, four, and fometimes, though very rarely, five roots. The roots fometimes ftand feparate, fometimes are concreted together; fometimes they are (trait, fometimes crooked. The fubftance of the teeth is compact. The corona is covered with a curious fubftance, called the enamel. This is thin, white, fhining, and, being the hardeft and moil compact fubftance in the body, is admirably adapted to the purpofes of maftication. It 13 fcarcely neceflary to remark, that in eating we only move the lower jaw, and that the upper is on all occafions fixed and immoveable, In the infant ftate, two fets of teeth are already ob- fcrvable in the jaw-bones. In the cutting of the teeth, the incifores firft make their appearance, in general about the eighth month; and afterwards, at about two years of age, two molares and the dog-tooth. The firft fet of teeth when complete is bun twenty in number, viz. eight incifores, eight molares, and four eanini. In the fecond fet are added twelve molares, viz. three on each fide in each jaw, making the complete fet in the adult thirty- two. To make room for this addition, the jaws undergo a gradual elongation. Hence the face is fo much lengthened from eight to eighteen years of age. About the feventh year the fecond fet begins to fupply the place of the firft, which by this time be- come loofe, by the wafte of the lockets and the growth of the teeth below. If we extend our views to the lower animals, we ihall find no part of the body more various among different Chap. 6.] Varieties in the -Teeth of Animals. 109 different races than the teeth. This circumftance is fo remarkable, that Linnasus has employed it in the diftribution of the firft clafs of animals (the mammalia) into its feveral orders. To enumerate all the varieties of teeth would be impofiible, and at prefent it would be fuperfluous. Let it be remarked, however, that they are not without their ufes, and that every animal experiences the advantages of its own peculiar ftruc- turc. [ no ] [Book CHAP. VII. BONES OF THE TRUNK. Spine or Back Bvnf. — JJciu the Head is mo-TjeJ. — The Thorax — - The Pf'vis. — Principal Marks cf DijUiitlion letweea the Male and Fttntde Skeleton* bones of the trunk are divided into thofe -*• of the fpine or back- bone, the thorax or chefl, and the pelvis. The fpine confifts of twenty-four pieces of bone called the vertebrae ; feven of thefe be- long to the neck, twelve to the back, and five to the loins. The thorax confifts anteriorly and latterly of twelve ribs on each fide of the fternum or breaft- bone, and part of the fpine behind. The pelvis is compofed of four bones; two ofia innominata or hip- bones; the os facrum, and the oscoccygis. That feries of bones called the fpine forms a co- lumn larger below than above, fmooth and round before, very rough and uneven behind, and hollow within. The bones of the fpine are joined to each Other by cartilages, in the centre of each of which is contained a fluid ; a curious circumftance of ftrufture firft difcovered by the kte Dr. Monro of Edinburgh. The chief advantage of this ftruc~ture is, that this fluid, when confined, has all the refinance of' a foiid body, without its hardnefs, which in this part might be attended with very bad confequences. The head is conn?cled to the upper vertebra of the neck bv two fmooth projections of that vertebra, which are called the condyls, being received into two correfponding cavicies in the under part of the cra- 9 mum- Chap. 7.] Motion of the Head. Hf nium. By means of this joint we move the. head backwards and forwards on the fpine, or perform the action of nodding. As it is neceffary, however, for the head to have alfo a rotatory motion, we here find a peculiar-icy of ftructure to which there is no- thing fimilar in any other part of the body. In the upper furface of the fecond vertebra of the neck there is a long tooth -like procefs or projection, which is received into a perforation of the firft vertebra. This procefs is rendered fmooth by a covering of cartilage ; it pafies quite through the vertebra above it, and is connected to this as well as to the cra- nium by ftrong ligaments, which give ftrength to the connection, and guard againft the effects of a too extenfive motion. The rotatory motions of the head, therefore, are not performed on the firft vertebra of the neck, but on the fecond ; the firft vertebra, with the head, moving on the tooth-like procefs of the fecond vertebra, as a wheel .moves on its nave. The fpine, however, though it forms a column, does not form by any means an upright column. The fpine, viewed tideways, if the os facrum is confi- dered as a continuation of it, is bent very much in the form of the letter/. In the neck it projects fome- what forwards, lower down it takes a curved direc- tion backwards, to make room for the heart and lungs, la the loins it advances again forwards under the center of gravity, io as to fupport the abdominal vifcera; and in the pelvis it recedes backv/ards, fo as confiderably to enlarge that cavity. Each vertebra is divided into a body and feven projections, apophyfes or proceffes. The body is placed before, it is fmooth, of a roundiih form, and a remarkably fpongy texture. The procefles are of a much firmer texture, and project backwards. TWO • of ill Vfes of the Spine. [Book IX; of thefe procefies are called the fuperlor oblique, and aicend obliquely from the upper part of the vertebra j two are called the inferior oblique, and defcend ob- liquely from the lower part j two are called the tranf- verfe, and project fideways j and orte is called the fpinous, from its refemblance to a thorn, which pro- jects directly backwards. Of thefe procefTes the fpinous and tranfverfe are the mod prominent. The oblique procefies feem chiefly defigned for the articu- lation of the vertebrae with each other* and are there- fore alfo called articular procefies. All the vertebras are perforated for the reception of the fpinal mar- row, and alfo have notches for the tranfmifiion of nerves. The ufes of the fpine are to fupport the "body iri ah erect pofture, and at the fame time, by the num- ber of joints with which it is furnifhed, to admit of a free motion, without danger of compreffing the fpinal marrow, which it is defigned to protect. It is formed larger below than above, becaufe the lower parts of it iiave a greater weight to fupport than the upper ; and bvcaufe, when the body is bent, that Weight acts with the longed lever againft that part of the fpine which is fartheft removed from it. In very young children, each vertebra confifts of three pieces of bone united by cartilage. As the fpine contains fo important a part as the fpinal mar- row, we obferve a felicitous care taken by Provi- dence, that the vercebrse Ihould not be disjointed* Befides being connected by ftrong ligaments, pro- portioned to the forces which are to be refilled, the vertebra of the neck enter into each other, thofe of the back are propped by the ribs, and thofe of the loins have fo large a furface of contact, as to render their reparation almoft impracticable. The Chap. 7;] Articulation of the Spine. 113 The thorax is a bony cavity, narrow above, wide below, and arched behind and at its fides. The fternum or breaft-bone, which forms the an- Kerior part of the thorax, is of a fpongy confidence, and of a fiat and nearly triangular form j in infancy it confifts of many parts, in the adult (late of only- two, or fometimes three. The upper part is broad and thick, the lower narrow and thin. The loweft part of the fternum, from its refemblance to a dag- ger, and its cartilaginous nature, is called cartilago enfiformis. The upper part of this bone is notched for the r afifage of the wind-pipe, and there are two cavities in its fides for the articulation of the cla- vicles or collar-bones. There are alfo feven fmall holes on each fide, for the articulation of feven ribs. Its ufes are to fupport the ribs, to protect the lungs and heart, and to furnifh connection to a mufcuiar organ, which will be afterwards confidered, called the diaphragm. The ribs which conftitute the greater part of the cavity of the thorax, are fomewhat of a femicircular form j they pafs from the fpine towards the fternum ; they are not connected, however, to the vertebras themfdves, but to the cartilagino-ligamentous fub- ftance which connects the vertebras to each other. At the pofterior part the rib has two procefies ; one of thefe, by which it is connected between two verte- bras, is called its head ; another is articulated with the tranverfe procefs of the vertebras immediately below, and is called its tuberofity. Advancing far- ther on this external furface, we obferve on moft of the ribs another fmaller tubercle, into which liga- ments connecting the ribs to each other, and to th~ tranfverfe procefies of the vertebra, and portions of the longifiimus dorfi, are infertedt Beyond this the ribs VOL. III. J make 114 VbeRtts. [Book IX, make a confiderable curve, fometimes called their an- gle. The ribs then begin to become broad, and continue fo to their anterior end, whereas near the fpine they are nearly round. To the fore end of each rib a long broad and ftrong cartilage is fixed, and reaches thence to the fternum, or is joined to the cartilage of the next rib. The ribs are twenty-four in number, twelve being placed on each fide. They are divided into the true and the falfe ribs j the feven uppermoft on each fide, which are connected to the fternum, being called true, and the remaining five falfe. The upper rib is fo placed, that its connection with the fternum is fomewhat higher than that with the fpine, and the two connections of the fecond rib are about horizontal j all the other ribs, however, point obliquely downwards, as they approach the fternum, and this obliquity increafes as we advance lower. A neceffary confequence of this ftructure is, that when the ribs are raifed, they muft be brought nearer to a right angle with the fpine, and that the cavity of the cheft muft be enlarged. The upper rib is fixed, but the, fecond and every fucceeding rib is-gradually more moveable than that placed immediately above it. The feven upper ribs, called the true ribs, are, as was before remarked, connected to the fternum 5 the three upper of the falfe ribs are not connected to the fternum, but adhere to each other, and to the cartila- ginous anterior part of the loweft of the true ribs. The two loweft of the falfe ribs are only connected to the fpine by one articulation, and have their other end no ctherwife fupported than by the mufcles and mem- branes with which they are furrounded. By thisftruo- ture the trunk of the body is rendered more flexible at its lower part, where moft motion is required. The ufes of the ribs are to form the lateral parts -of the Chap. 7-] 'fhe Pelvis.' n£ the thorax ; to render the cavity of the thorax larger or fmaller in breathing -, to protect the vifcera of the thorax ; to give origins and infertions to a variety of mufcles ; and to fupport the mammae or breads. The pelvis, fo called from its reiemblance to a bafin, conftitutes the -lowed part of the trunk. Its pofterior part is formed by the os facrum, and its lateral and an- terior parts by the ofia innominata. The os facrum may be ccnfidercd as a continuation of the fpine; and fome anatomifcs have called both, this bone and the oscoccygis by the name of thefalfe vertebras. The os facrum is a large thick bone, of a triangular form j its broadeft part is placed upperrnod, and its narrowed is turned downwards and inwards. The poderior furfaee of this bone is convex, the an- terior concave. The two lateral margins of it are in- crufted with cartilage, by the help of which it is im- moveably connected with the offa innominata. In the middle of this bone there is a canal for the fpinal mar- row, correfponding with that in the vertebrae of the fpine ; and on the anterior furfaee there are ten per- forations, for the paflage of as many nerves. On the poderior part there are many protuberances, which, like the prbceffes of the vertebrae, ferve for the infer- tion of mufcles,. The os coccygis is a fmall bone of a pointed fhape, adhering to the lower part of the os facrum. The os, coccygis is in infancy compofed of feveral pieces of bone, which coalefce, however, in the adult date. It may.be confidered as a continuation of the os facrum, and is bent in the fame direction with that bone. Theoffa innominata, which form the fides and fore part of the pelvis, are two large broad bones, which iri infancy confid each of them of three clidinct pieces $ but as we advance in life, the intermediate cartilages J 2 -gradually u£ I launch Bone, &c. [Book IX, gradually ofiify, and the marks of the original reparation difappear, fo that they become one irregular bone. They ft ill, however, retain the names of ileum, ifchium, and pubis, by which their divifions were originally dif- tihguimed, and are defcribed as three different bones, by *-he generality of anatomifts. The offa innominata are connected pofteriorly to the os facrum, by a firm cartilaginous fubftance. The os ileum or haunch-bone, forms the higheft and moft confiderable part of the os innominatmn. The external fide of the ileum is unequally convex, and is called its dorfum : the internal concave furface is by fome authors named its cofta. The fernicircular edge at the higheft part of this bone, which is tipped with cartilage in the recent fubject, is named the fpine. This has two confiderable projections ; one anterior, and the other pofterior, which is the larger of the two. Thefe ends of the fpine being more prominent than the furface of the bone below them, are therefore called the anterior and pofterior fpinous procefles. Below the anterior fpinous procefs another protuberance pro- jects, which by its fituation may be diftinguifhed from the former, by adding the epithet of inferior. Between thefe two anterior procefTes, the bone is hollowed. Below the pofterior fpinal procefs a fecond protube- rance of the edge of this bone is alfo to be obferved, which is clofely applied to the os facrum. Under this laft procefs a ccnfiderable niche is oblervable in the os ileum j between the fides of which and the ftrong liga- ment which is ftretched over from the os facrum r.o the /harp-pointed procefs of the os ifchium of the recent fbbject, a large hole is formed, through which the wnufculus pyriformis, the great fciatic nerve, and the pofterior crural veffels, pafs, and are protected from compreffion. The internal furface of the os ileum is concave Chap. 7.] Hip Bones. uy •concave in its broadeft fore part, whence a fmall finuo- fity is continued obliquely forwards, at.the infide of the anterior fpinous proc while, at the lower end, it moves in a fort of cycloi.d upon the round part of the ulna; and as the hand is here articulated and firmly connected to the radius* they muft move together. The ulna, being connected by a hinge -joint to the os brachii, has fcarcely any other motion than that of flexion and extenfion, in which it carries with it the radius. The motions of the hand, in which the palm is turned either upwards or downwards, are performed by thofe of the radius on the ulna, carrying with it the hand, From thefe cir- cumltances it appears, that the ulna more particularly belongs to the os humerij and the radius to the car- pus. The ulna fometimes carries with it the radius, but the radius never moves the ulna, which, like the tibia is connected by a hi^ge -joint, and has motion only in Chap. 9.} Bones of tie Hand. 131 in two directions. The radius is fo intimately con- nected with the hand, and is fo much employed In its principal motions, that it has been called manubrium waxus, or the handle of the hand. Without this pe- culiar mechanifm, the motions of the fore-arm would be as confined as thofe of the leg ; but providence, which has preferred the more firm and fecure ftruc- ture in a part which was deflined to fupport the body, has adapted the fore-arm, by this beautiful and admi- rable contrivance, for the performance of a number of motions, with which a hinge -joint would be quite in- compatible. The bones of the hand are divided into thofe of the carpus, metacarpus, and fingers. The carpus or wrift is formed of eight bones, which are fmall, of irregular lhapes, and diftinguiflied into two feries. The form of the carpus isfquare ; that furface, which is contigu- ous to the palm of the hand, is concave, the oppofite is convex. Each of the two feries of bones, which, compofe the carpus, confiils of four pieces. The firfl feries, or that which is placed next die bones of the fore-arm, confifts of the os naviculare, the os femilu- nare, the os cuneiforme, and the os pififorme. The bones, which form the other feries, are the os multan- gulum majus, the os multangulum minus, the os ca- pitatum, and the os cuneiforme. Thefe bones are co- vered with cartilage, and are varioufty articulated with the bones with which they are in contact. The prin- cipal ufe of fo great a number of bones in the wrift is to render the hand more flexible. The back part of the hand is convex, for greater firmnefs and flrength ; the palm concave, fbr containing more furely and con- veniently fuch bodies as we take hold of. The upper part of the hand has an obfcure motion in comparifon the remainder, and ferves as a bafe to the fingers. K 2 With 13 a Skeleton of [Book IX. With refpect to the metacarpal bones, and thofe of the fingers, they are fo nearly fimilar to thofe of the metatarfus and toes, that nothing need be added con- cerning them. The reader muft undoubtedly have been flruck with the great refemblance of ftrufhire between the in- ferior and ftiperior extremities. The os humeri has many points of refemblance to the os femoris, the tibia and fibula to the radius and ulna, and the bones of the carpus, metacarpus, and fingers to thofe of the tarfus, metatarfus, and toes. Before the anatomy of the bones, however, is con- cluded, it will be proper to make a few general re* marks on the fkeleton of quadrupeds. ^In quadrupeds we obferve the fame general out* lines of ftrufture in the ofleous fyftem as in man. Their fkeletons divide themfelves into head, trunk, and extremities ; and each of thefe divifions bears a ftriking refemblance to the fame divifion in the fkele- ton of the human body. The cavity of the cranium is much fmaller in quadrupeds than in man, in pro- portion to the other parts, but the bones of the face are much longer ; and with refpect to this circum- ftance, as well as many others, the monkey holds a middle place between mankind and quadrupeds. The fpine, as in man, is connected to the cranium j but in quadrupeds, this bony column, inftead of be- ing placed vertically, is placed horizontally j in both, however, the ftrticture is the fame, and the part is fubfervient to the fame purpofes. The other parts of the trunk are alfo very fimilar to the fame parts in man j and the form and relative fituation of the fter- num and ribs are nearly the fa -it but the latter are more numerous in quadrup - ''.e fame refem- blance is manifefted in the bones of the pelvis, ex- cept Chap. 9.] Quadrupeds. 133 cept that the os coccygis is continued beyond the other parts of the body, and forms the tail. The upper part of both extremities, as in man, is formed of one piece of bone, the lower part of two, and in many quadrupeds there are bones which correfpond with the carpus and tarfus, the fingers and the toes. The clavicula or collar-bone is in general, however, want- ing in quadrupeds, and is only found in monkeys, fquirrels, and fome other animals, which are fkilful in climbing, and whith employ their fore legs for other purpofes than that of travelling. In fhort, the fkeleton of the quadruped is fo fimilar to that of man, that when the Ikeleton of the former is placed eredb on the hind- legs, it may eafily, by perfons unac- quainted with anatomy, be miftaken for that of the latter. The figure in Plate II. reprefents a front view of the human fkeleton, with fome of the ligaments and cartilages, which connect the bones to each other. HEAD and NECK. a, Os frontis. by Os parietale. Between a and b, part of the coronal future. c, The pars fquamofa of the temporal bone. Between b and c, the fquamous future. Below the pars fquamofa, the zygoma ; and, lower down, above/, the maftoid procefs. Between the pars fquamofa and the cavity, which contains the eye-ball, called the orbit > the tempo- ral procefs of the fphenoid bone is feen. d, Os make. Above d, a portion of the tranfverfe future. c., Os maxillare fuperius, with the eight teeth of th$ right fide, K3 The 134 Defcription [Book IX. The nafal procefs of the fuperior maxillary bone has the os nafi joined, by the lateral nafal fu- ture, to its infide j and at the outf^de, within the orbit, the os unguis. The offa nafi joined- to each other before, by the anterior nafal future. /, Os maxillarc inferius with fixteen teeth; the foiar anterior named incifores, the two corner ones caniniy and the five pofterior on each fide mo/ares. Oppofite to/, t!i£ angle of the lower jaw; above /, the condyloid procefs, by which the jaw is connected to the temporal bone, at the root of the zygoma ; and behind the os mate, the co- ronoid procefs. jj, The feven cervical vertebrae, with their interme^ diate cartilages. Oppofite to £, their tranverfe procefles. TRUNK. a 3 Sternum. a, its middle piece, to which one half of the carti- lage that connects the fecond rib, the whole of tke cartilages of the third, fourth, fifth, fixth, and one half of the feventh, are fixed. Above #, the firft or upper triangular piece, to which the clavicle and one half of the cartilage that connects the fecond rib are fixed. Below a, the extremity, or third piece of the fternum, named the cartilago evjiformisy to which one half of the cartilage that connects the feventh rib is fixed. I, The feventh, or laft true rib. c, The twelfth, or laft of the five falfe ribs. d, The five lumber vertebra^ with their intermediate cartilages. Oppofite Chap. 9.] of the Plates. 13$ Oppofite to dy their tranfverfe proceiles. ty The os facrum, with its five divifions. fy Os innominatum, divided into gy Os ilium, by Os pubis, i} Os ifchium, Oppofite to /, the foramen thyroideum. SUPERIOR EXTREMITY. a, The clavicle, fixed before to the firft piece of the (lernum, and outwards to the acromion of th§ fcapula, l>3 The fcapula. Above by the cervix of the fcapula. Oppofite to it, the inferior cofta ; and below the outward extremity of the clavicle, the fuperior cofta, and coracoid procefs, are feen. ft the os humeri. The upper end of it, which is connected to the cavity of the fcapula, named the glenoldy below the acromion, is named its bead or ball ; on each fide of which is feen the tubercles, named the external and internal •> and between thefe, a groove for lodging the long head of the biceps flexor cubiti. d> The internal condyl. e, The external condyl. Between d and e, the trochlea, upon which the ulna moves. /, The radius. The upper end, which moves on the external c©n^ dyle of the os humeri, is named its head-> below that, the tubercle for the infertion of the biceps flexor cubiti, and between thefe the cervix. The inferior end of it is connected to the carpus. K4 I 3 6 Defcription Book I X* £, The ulna. The upper end of it forms the coronoid procefs, for the infertion of the brachialis mufcle. The inferior end has a procefs named the ftyloid-, which is connected to the carpus by a liga- ment. h, The carpus, formed of eight bones. iy Metacarpal bone of the thumb. k, The metacarpal bones of the four fingers. /, The two joints of the thumb. m, The three joints or phalanges of the fore- finger ; and the fame are feen in each of the other three, INFERIOR EXTREMITY. a, The os femoris. The upper end of it is named its head or ball, which is lodged in a deep focket of the os in- nominatum, named the acetaluhm. Between the head and trochanter major, the cervix. £, Trochanter major. £, Trochanter minor. ds Internal condyl. e, External condyl. /, Patella. The place where it moves upon the os femoris, is named the trochlea. Z> Tibia, Between the tibia and the condyls of the os fe- moris, the femilunar cartilages are feenj an<3 below the joint, the tubercle of the tibia. b. Fibula. ?, Malleolus internus. li Malleolus externus, /, Og Chap. 9.] tf the Plates. 137 /, Os calcis. Between / and m, the other fix bones of the tar- fus, m> Metatarfal bones of the four toes, #, The three joints, or phalanges, of the four toes. Cy Metatarfal bone of the great toe. jp, The two joints of the great toe. The figure in plate III. reprefents a back view of the human fkeleton, with fome of the ligaments and cartilages which connect the bones, HEAD and NECK. 0, Os parietale, joined to its fellow by the fagittal future. £, The os occipitis, joined to the parietal bones by the lambdoid future, which is between a and b. ft Os mate. dy Maxilla inferior, with a view of the teeth of both jaws from behind. e, Tphe feven cervical vertebra?. TRUNK. a, The feventh or laft true rib, by The twelfth or laft rib. Cy The five lumber vertebrae. dy Os facrum. €y Os coccygis. ' /, Os innominatum, divided into gy Os ilium. by Os pubis. /, Os ifchium. SUPERIOR EXTREMITY* »y The clavicle, joined outwards to the acromion of the fcapuU. £, The J3* Defection 6/tbg Plates. [BooklX. #, The fcapula, £y Os humeri. dy Internal condyl, 6y External condyl, /, Radius. g, Ulna, its upper end, named okcranon j and near the wrift, its ftyloid procefs, l>, The eight bones of the carpus. », The metatarfal bone of the thumb, £, The metatarfal bones of the four fingers. /, The two joints of the thumb. >z, The three joints or phalanges of the four fingers, INFERIOR EXTREMITY, «, Os femoris, ^, Trochanter major, and at the infield of it tjicr cervix. c, Trochanterjrsinor. d, Internal condyl. t, External condyl. /, Tibia. gy Fibula. by Malleolus internus. /, Malleolus externus. >, The feven bones of the tarfus. /, The rpetatarfiis. w, The joints or phalanges of the tolj. Chap. 10.] [ 139 ] CHAP. X. STRUCTURE OF THE MUSCLES. General Defcription of Mufcles.— Olfervaticns of the AbUe Fontana.-^ OfLnvenboeck.—Mufcfescompofed of fmall Fibres. — StruSlurt o£ different Mufcles.— -Ant agonijls. — Mufcles of the Fcetus* TH E bones, confidered with relation ,to the mo- tions of the body, are merely levers ; let us now confider the ftructure of the mufcles, which are the immediate fources of all the motions of the animal machine. The animal fubftance, which the anatomift calls mufcle, is that which in common language pafles under the name of the lean or flefh of meat. The colour of the mnfcles, when they are firft removed from the body, is red ; this colour, however, is not eflential to them, but is merely owing to the prefence of blood, for when mufcle is cleanfed from blood, it appears white. In every recent mufcle we may at firft view diftinguifh two kinds of fibres ; the one kind appears red, and is the true mufcular fubftance; the other is tendinous, has a white filvery appearance, and has no power of contraction like the former. The tendinous fubftance is fometimes collected ,into a cord, but is very frequently expanded, fo as by covering the furface of a mufcle, or by pervading its fubftance, to afford a very extenfive connexion to mufcular fibres. The Abbe Fontana has taken great pains to examine the ftructure of mufcles. He divided mufcular fubftance with the point of a fmall needle till he came to minute threads, which, whatever pains he took, would admit of no further divifion. Thefe, he examined with a lens, 2 the 140 Mujcular Fibres. [Book IX. the diameter of which was one-ninth of an inch; when they appeared to be folid homogeneous cylinders, in- terrupted at regular diftances by very minute lines or wrinkles. Thefe wrinkles, when they were examined in different points of view, might have paffed for glo- bules j but upon this circumftance, as the obfervation went no further, the Abbe does not infift. This un- dulated appearance has alfo been obferved in nervous and tendinous fibres, examined by microfcopes of high magnifying powers. Dr. Monro, in his obfervations on the nervous fyftem, gives it as his opinion, that they are to be confidered as folds or joints, ferving to accommodate the parts to the different ftates of flexion and extenfion. In proof of this he finds, that thofe parts which have this appearance in their re- Jaxed ftate, lofe it when ftretched. Lewenhoeck long ago fancied that he had difcovered the ultimate mufcular fibre, which he confidered as being one hundred times as fmall as a hair. He af- terwards, however, candidly acknowledged, that what he fuppofed to be a fimple fibre, was, in fact, a bun- dle of them. Notwithftanding, therefore, the rni- crofcopical obfervations of the Abbe Fontana, and other philofophers, we muft flill acknowledge our- felves ignorant of the ftructure of the ultimate com- ponent parts of rnufcular fubftance j and all we are allowed to fay is, that their ftructure is fibrous. Thefe minute fibres, obferved by. the Abbe Fort- tana, were tied by cellular fubflance in fmall fafci- culi or bundles, thefe bundles are again formed into larger by the fame means, and of thefe fafciculi are compofed thofe contractile maffes of flefh called mufcles. Mufcles are generally connected at their two extre- mities to bones, by means of tendons; the largeft part of Chap. 10.] Connexion of Mufcles i 14* of a mufcle is called its belly, and is chiefly compofed of contractile mufcular fibres. That connexion of a mufcle which is leaft moveable is called its origin, that which is moft moveable its infertion : but thefe terms are in many cafes merely relative, for a part of the body which is more fixed in one pofture becomes lefs fo in another. The fibres which compofe a mufcle run either longitudinally, tranfverfely, obliquely, or circularly. If all the fibres which compofe a mufcle run in the fame direction, it is called rectilinear; ra- diated, if the fibres are difpofed like radii ; penniform, if, refembling the plume of a feather, the fibres are fituated obliquely with refpect to the center from which they proceed ; compound, if the fibres run in differ- ent direction* The majority of the large mufcles of the body are compound. Moft mufcles have others oppofed to them, which act in a contrary direction, and are called antagonifts. • Thus, one mufcle, or one fet of mufcles, bends a limb, another extends it ; one elevates a part, another depreffes it; one draws it to the right, another to the left. By thefe ,oppofite powers the part is kept in a middle direction, ready to be drawn either one way or another, as particular mufcles are thrown into ftronger action. The flexor mufcles exceed the extenfors in ftrength, and for this reafon the eafieft poftures are thofe in which the body or limbs are mo- derately bent. When we fpeak of the mufcies of a part, we do not mean thofe which are fituated on it, but thofe which ferve to move it. Thus, what are called the mufcles of the leg, and which are fubfervient to its motions, are placed round the thigh bone; thofe which move the foot, round the bones of the leg, &c, In 14! Mujclestfthe Fates. [Book IX, In the foetus the mufcles are evidently inferred into the pericfteum only, but in the adult ftate, when the periofteum adheres much more clofely to the bone, the tendons, being confufed with the pe- riofteum, pafs with that even into the foveoli of the bone. C H A P. XL MUSCLES OF THE HEAD. nfifies of the Forehead.— Of the Eye-lid:.— Of the Eje.—Oftk jfofe.— Mufcles of the Jvlouth. — Why the Face is the Index to thf Mind*— Temporal Mufcles. — Mufcla cftbe Neck.— Of the Jaw, — The Tongue. — Mufcles of the Palate, &c* THE (kin which covers the head is moved by a fmgle broad mufcle, and one fmall pair. The former of thefe is fitiiated immediately below the com- mon integuments, at the back and fore part of the head, with the intervention of a broad tendon, and is called occipito frontalis. Its effeft is to draw the (kin of the head backwards, to raife the eye-brows, and wrinkle the (kin of the forehead. The corrugator fupercilii arifes from the internal an- gular procefs of the os frontis, near its joining with the bones of the face ; it is inferted inro the inferior and inner part of the occipito frontalis, draws the eye-brows towards each other, pulls downwards thefkinofthe forehead, and caufes it to wrinkle, particularly be- tween the eye -brows. The mufcles of the ear will "be fpoken of when it becomes neceffary to treat of the organs of hearing. The mufcles-of the eye-lids are, the orbicularis pal- pebrarum, which furrounds the eye, and has the effect of (hutting the eye-lids. The upper eye -lid has alfo a mufcle proper to itfelf, called the levator palpebrse fu- perioris, the effect of which is to raife the upper eye- . lid, and confequently to counteract the former. The ball of the eye has fix mufcles, four ftrait and two oblique. The ftrait mufcles all rife from the bot- tom 144 Mufcles of the Eye &nd Nofe. Book IX. torn of the orbit around the foramen, through which the optic nerve paries, and are extended to the ford part of the globe of the eye. Thefe mufcles are named from their life. The levator oculi raifes the ball of the eye, the depreffor pulls it down, the adductor turns the eye towards the nofe, and the abductor moves the globe outwards. The two oblique mufcles are, the obliqims fuperior or trochlearis, which, rifing from the bottom of the orbit, runs along the pars plana of the ethmoid bone to the upper part of the orbit, where its tendon paffes through a cartilaginous ring connected to the os frontis, by which mechanifm the direction of its force is altered, and its tendon afterwards proceeding a little downwards, and directed outwards at the fame time, is inferted half way between the infertion of the attollens oculi and optic nerve. The effect of this curious mufcle is to roll the eye, to turn the pupil downwards and outwards, and to draw the whole ball nearer to the nofe. The obliquus inferior arifes from the orbitar procefs of the fuperior maxillary bone, and running obliquely outwards is inferted in the fpace be- tween the abductor and optic nerve. Its ufe is to draw the globe of the eye forwards, inwards, and down- wards, and, contrary to the fuperior oblique, to turn the pupil upwards towards the inner extremity of the eye-brow. By acting fucceflively with all the mufcles of the eyes we are able to roll them. The nofe is affected by feveral mufcles of the face, but only one pair is commonly confidered as properly belonging to it. This, which is called the ccmpreffor naris, arifes externally from the root of the alas nafi, and running obliquely upwards along the cartilage of the nofe, joins its fellow, and is inferted into the neigh- bouring bone. The effect of this mufcle is to comprefs the alse towards the feptum naris, particularly when we want Chap. II.] Mujcks of the Mouth. 145 want to fmcll acutely j it alfo wrinkles the fkin of the nofe. The mouth has nine pair of mufcles inferted into the . lips, where their terminations form a fmgle mufcle, which furrounds the mouth. One of the fe .rife s from the upper jaw-bone, and is inferted into the angle of the mouth. Its efFeft is to raife the corners of the mouth, and it is therefore called the levator anguli oris. 2. The levator labii fuperioris ateque nafi. This rifes by two diftincl: origins ; one of thefe proceeds from the fuperior maxillary bone immediately below the orbit, the other from the fame bone at the inner angle of the eye. It is inferted partly into the upper lip and partly into the outer part of the alas nafi, raifes the upper lip towards the eyes and a little outwards, and alfo dilates the noilrils, by drawing the ate nafi upwards and out- wards. 3. The deprefTor labii fuperioris alaquas nafi, arifes from the upper jaw-bone, where thedentes incifivi and canini are fixed, and is inferted -into the upper lip -and root of the ate nafi. When it acts, it draws the upper lip and ate nafi downwards and backwards. The three mufcles of the mouth, already mentioned* are fituated above, the three other pairs are placed be- low. 4. The depreffor anguli oris arifes from the lower •edge of the maxilla inferior, and is alfo connected to the neighbouring foft parrs. It is inferted into the corners of the mouth, and pulls them downwards. 5. The depreffor labii inferioris arifes from die inferior part of the lower jaw-bone, near the chin, is inferted into the edge of the lower lip, and pulls it downwards and a little outwards. 6. The levator labii inferioris arifes from the lower jaw, where the dentes incifivi and. canini are fixed, and, being inferted into the under lip and fkin of the chin, draws them upwards. VOL, III, L Three 1 46 Mufcles of the Face. [B ook IX* Three pair of mufcles are alfo feated outwards with refpect to die mouth. 7. The buccinator (or trumpeter) arifes from both jaws, adheres clofely to the membrane of the mouth, and is inferted at its angles. Its effect is to draw the angles of the mouth backwards and outwards, and to contract its cavity, as in blowing a wind i.nftrument, and in pufhing our meat between the teeth. 8. The zygomaticus major arifes from the os malas, near the zygornatic future, and is inferted into the angle of the snouth. When it contracts, it draws the angles of the mouth upwards and outwards, and makes the cheeks prominent as in laughing. 9. The zygomaticus minor defcends obliquely from the prominent part of the os malse, and is inferted into the upper lip near the cor- ner of the mouth. Its ufe is to draw the corner of the mouth obliquely upwards and outwards towards the external corner of the eye. The fmgle mufcle, which was mentioned as being formed by the terminations of all the others decuflating each other, is called the orbicularis oris, and entirely furrounds the mouth. x Its ufe is to (hut the mouth, by contracting and drawing both lips together, and to counteract all the mufcles which contribute to its for- mation. The mufeles of the face are the organs, which, be- ing affected by the paffions, render the human counte- nance an index of what is paffing in the mind ; and, as all mufcles acquire a greater degree of ftrength as well as pronenefs to action in proportion to the degree in which they are employed, fo the countenance becomes imprefied with a general character, which is the foun- dation of phyfiognomy. For this reafon the counte- nances of old people are more exprefTive, and their likencflbs ittgre. eaiily taken, than thofe of the young, thougb Chap, it.] Phyfiogriomy. 147 though this is partly to be attributed to the wafting of the fat, which in youth fills the interftices between the mufcles, and prevents ftrong lines. To the -above prin- ciple is to be attributed the greater expreflionobfervablc in the countenance of a perfon of a cultivated mindy than in that of a perfon whofe flock of ideas is limited. From all thefe circumftances it appears, that the culti- vation of the mind is the moft likely method of iti- creafmg the expreffion and beauty of the countenance. The mufcles of the lower jaw are four pairs, and are thofe employed in the maftication of the food. The temporalis mufcle has a very extenfive origin^ from the lower and lateral part of the parietal bone, all the pars fquamofa of the temporal bone, from the ex- ternal angular procefs of the os frontis, and from the temporal procefs of the fphenoid bone. From thefe different origins the fibres defcend like radii towards the jugurti, under which they pafs, and are inferted into the coronoid procefs of the lower jaw. Its ufe is to prefs the lower jaw againft the upper, and at the fame time to draw it a little backwards. This mufcle is covered with a broad te,ndon, called its aponeurofis* which defends it, and gives origin to a great number bf mufcular fibres. The mafTeter arifes from the Superior maxillary bone, where it joins the os malse, and from the inferior ajid anterior part of the jugum, and is inferted into the angle bf the lower jaw, which, when it a6bj it prefies againft the upper. The pterygoideus internus proceeds from the inner and upper part of the internal plate of the pterygoid proceis of the fphenoid bone, and from the pterygoid procefs of the 6s palati. It is inferted into the angle of the lower jaw internally ^ and, when it ads, draws it upwards and obliquely towards the pppofite fide. L2 the 148 Mufcks cftbe Head, &V. [Bookltf, The pterygoideus externus takes its origin from the outer fide of the pterygoid procefs of the fphenoid bone, from part of the tuberofity of the os maxillare adjoining to it, and from the root of the temporal pro- cefs of the fphenoid bone. It is inferted into the neck of the condyloid procefs of the lower jaw, and pulls it forwards and to the oppcfite fide, or when both the external pterygoid mufcles a£t, the fore teeth of the under jaw are pufhed forwards beyond thofe of the upper jaw. On the fide of the neck, towards its fore part, are two mufcles. The external of thefe is a mufcle of the fkin, and is called platifma myoides. It arifes by a number of (lender fibres from the cellular fubftance, which covers the upper parts of the deltoid and pec- toral mufcles; in their afcent they all unite to form a thin miifcle, adhering to the fkin, and which is inferted into the lower jaw. It draws the fkin of the cheek downwards. The fterno-cleido-mafloideus has two origins, one from the fternum, the other. from the clavicle, which, uniting, form one mufcle, which runs oliquely upwards and outwards, and is inferted into the maftoid procefs of the temporal bone. When it contracts, it turns the head to one fide, and bends it forwards ; or when its fellow ads with it, they draw the head directly for- wards. Six pair of mufcles are fituated between the os hyoides and the lower jaw. The mufcle, which forms the external layer, is called the digaftricus. It rifes near the maftoid procefs, runs downwards and forwards to the os hyoides, and thence proceeds to the bone of the chin, into which it is in- ferted. When it>ad:s, it pulls the lower jaw, down- wards and backwards, and therefore opens the mouth, 6 When Chap, ii.] tfbe Tongue, &c. 149 When the lower jaw, however, is fixed by the ftronger jnufcles, which have been already defcribed, the effect of the digaftricus is different, for the os> hyoides, then becoming the more moveable part, is drawn upwards, and with it the larynx and pharynx, as in the act of fwallowing. The mylo-hyoideus paffes from the infide of the lower jaw to the os hyoides, and has nearly the fame effect as the digaftricus. The genio-hyoideus alfo pafles from the os hyoides to the chin, and either raifes the former or pulls down the latter, according as the lower jaw or the os hyoides is rendered more fixed by other mufcles. The genio-hyo-gloffus arifes 'from the lower jaw, and is inferred partly into the os hyoides, and partly into the tongue. This mufcle, according to the di- rection of its fibres, acts very differently on different occafiens; from the feparate action of its fibres it either draws the tongue backwards-, extends it out of the mouth, or renders its upper part concave. Two mufcles pafs from the os hyoides to the trunk. The fterno-hyoideus proceeds from the- fternum, and pulls the os hyoides downwards. The omo hyoideus arifes from the fuperior cofta of the fcapula, and draws the os hyoides obliquely downwards. It is to be noticed, that when there are two mufcles of equal ftrength and equal obliquity attached to a moveable part, and they both act together, they draw it in a Itrait line, the obliquity of the one counterbalancing that of the other. The fubftance of the tongue is mufcular, and is diftinguifhed by anatomifts into fix pair of mufcles, which it cannot be neceffary to enumerate. They alfo defcribe fix pair of mufcles belonging to the pharynx : thefe I mall pafs over in filence, and merely L 3 confider 150 Palate, &c. [Book IX. confider it as a mufcular bag, forming the upper part of the alimentary canal. There are alfo feveral muf- cles belonging to the palate and uvula, of which the limits of this work do not permit the fpecification. I ihall at prefent alfo pafs over the mufcles of the la- rynx, as a better opportunity will occur of compre- hending them under the defcription of the parts ta which they belong. The fame obfervation is appli- cable to the mufcles of the ear. Chap. 12,3 £ 151 3 CHAP. XII. MUSCLES OF THE TRUNK. Mufcles of the Nick and Back.— Of the Brea.ji.~- Of the Ribs. — The Diaphragm,— Mufcles of the Abdomen.— Of the Pelvis, tfr. ON the anterior part of the neck, clofe to the ver- tebra, are feated the following mufcles : The longus colli arifes from the bodies of three o/ the vertebras of the back, and from the tranfverfe proceffes of moft of the vertebrae of the neck. It is inferted into the fore part of all the vertebras of the neck, and has the effect of drawing it forwards or to one fide, according as the mufcle on both fides, or that on one only, is called into action. The rectus capitis internus major proceeds from the extremity of the tranfverfe procefies of the third, fourth, fifth, and fixth vertebras of the neck, is inferted into the cuneiform procefs of the os occipitis, and bends the head forwards. The rectus capitis internus minor arifes from the fore part of the body of the firft vertebra of the neck, is inferted into the condyloid procefs of the os occi- pitis, and alfo bends the head forwards. The rectus capitis lateralis arifes from the anterior part of the point of the tranfverfe procefs of the firft vertebra of the neck, and is inferted into the os occi- pitis, and bends the head a little to one fide. The large arid ftrong mufcles, feated at the pofte- rior part of the trunk, may be divided into four layers and a fingle pair. The external layer confifts of two very broad mufcles, L4 The 1 5 2 Mufcles of the [Book IX* The trapezius arifes by a ftrong round tendon, from the middle of the os occipitis, and from a rough curved line, which extends thence towards the ma- ftoid procefs of the temporal bone. It proceeds downwards along the nape of the neck, is attached to the fpinous procefies of all the vertebrae of the back, and the two loweft of the neck, and is. alfo firmly connected by the intervention of a tendon- to its fellow of the oppofite fide. It is inferted into the pofterior part of the clavicle, the acromion, and almoft all the fpine of the fcapula. It moves the fcapula either obliquely upwards, directly backwards, or ob- liquely downwards, according as its different parts are called into action. The latiflimus dorfi arifes, by a broad thin ten- don, from the ppfterior part of the fpine of the os ileum, from the fpinous procefies of the os facrum, loins, and feven inferior of the back, and from -three or four of the lower ribs j its fibres converging pafs over the inferior angle of the fcapula, are collected into a -flat cord in the axilla, and inferted into the os humeri. Its action is to pull the arm downwards and backwards, and to roll the os humeri. The fecond layer of mufcles confifts of three pair* two on the back and one on the neck. On the back are feated the ferratus pofticus inferior. This mufcle originates from the fpinous procefles of the two infe- rior of the back and three iuperior vertebrse of the loins, is initrted into the four loweft ribs, which it draws downwards, and is therefore a mufcle of ex- piration. The rhomboideus proceeds from the fpinous pro- ceflcs of the five fuperior vertebras of the back and three inferior of the neck, and is inferted into the bafe ef Chap. 12.] Neck and Back, &V. 153 of the fcapula, which it draws obliquely upwards, and directly inwards towards the fpine. On the neck is fituated. The fplenius, which arifes from the fpinous pro-? ceffes of the four upper vertebrae of the back and five lower of the neck ; it is inferted into the tranfverfe proceffes of the five fuperior vertebra? of the neck, the poflerior part of the maftoid procefs, and the os occipitis, -where it joins the root "of that procefs* When one of thefe mufcles acts, it brings the head and neckly obliquely backwards, or, when they both act, they draw the head diredtly backwards. The fingle- pair, which was mentioned* is the Serratus pofticus fuperior. This originates from the fpinous procefTes of the three lowed vertebras of the neck, and two uppermoft of the back, and is in- ferted into the fecond, third, fourth, and fifth ribs. Its effect is to elevate the ribs, dilate the thorax, and confequently it is fubfervient to infpiration. Having removed thefe mufcles, we come to the third layer, which confifts of three on the back, and three on the neck. On the back are, The fpinalis dorfi, which arifes from the fpinous precedes of the two uppermoft vertebrae of the loins and three inferior of the back, and paries to the nine uppermoft fpinous proceffes of the vertebras of the back. The evident effect of this mufcle is to ftraiten the fpine, and prevent it from bending forwards. The longiflimus dorfi originates from the fide of the os facrum, and its fpinous proceffes j from the pofterior fpine of the ileum ; from all the fpinous procefles, and from the roots of the tranfverfe proceflcs of the vertebras of the loins. It is inferted into all the tranfverfe procefies of the vertebras of the back, and 1 54 Mufrlcs of tie [Book IX « and alfo into the lower edge of the. ten uppermoft ribs, near their tubercles. This mulcle flrengthens the fpmc, and keeps the body from bending for- wards. The facro-lumbalis, which ariles in common with the longiffimus dorfi, is inferted into all the P'JS near their angle. It pulls down the ribs, and affifts in creeling the trunk of the body. On the neck we find, the Complexus, which arifes from the tranfverfe pro- eeffes of the feven fuperior vertebras of the back and four inferior of the neck ; it is inferted, with the tra- pezius, into the inferior edge of the protuberance in the middle of the os occipitis, and into a part of the curved line which runs towards the maftoid procefs. When they both ad, they draw the head directly backwards, or obliquely fo when only one is called, into action. The trachelo-maftoideus, which arifes from the tranfverfe proceffes of the three uppermoft vertebras of the back, and from the five lowermoft of the neck, where it is connected to the tranfverfus cervicis, is inferted into the pofterior part of the maftoid procefs, It affifts the complexus, but pulls the head more to one fide. The levator fcapulse arifes from the tranfverfe procefles of the five fuperior vertebras of the neck, and is inferted into the fuperior angle of the fca^ pula. It elevates the fcapula, and draws it a little forwards. The fourth layer confifts of two pair on the back, two on the pofterior part of the neck, four fmall pair* fituated immediately below the pofterior part of the; occiput, and three on the fide of the neck, Qn the back are the Chap. 12.] Neck, Back, fcfr. 155 Semifpinalis dorfi, which arifes from the tranTverfe procefTes of the feventh, eighth, ninth, and tenth ver- tebrae of the back, is inferted into the fpinous procefies of all the vertebras of the back above the eighth, and into the two lowermoft of the neck. Its effect: i*to extend the fpine backwards. The multifidus fpinas originates from the fide and fpinous proceftes of the os facrum,and from the pofte- riorpartoftheos ileum, where it joins thefacrum; from all the oblique and tranfverfe procefles of the vertebras of the loins j from all the tranfverfe procefles of the vertebras of the back, and from thofe of the neck, ex- cept the three upper j its tendinous and mufcular fibres run in an oblique direction, and are inferted into the fpinous procefies of all the vertebras of the loins, of the back, and of the neck, except the firft. When one fide of this mufcle ads by itfelf it extends the fpine obliquely, when both act they draw it directly back- wards. On the poflerior part of the neck are the femifpina^ lis colli, which arifes from the tranfverfe procefles of the fix uppermoft vertebras of the back, and is inferted into the fpinous procefles of all the vertebras of the neck. It extends the neck backwards. The tranfverfalis colli, which proceeds from the tranfverfe procefles of the five uppermoft vertebra of the back, and is inferted into the tranfverfe pro- cefles of all the cervical vertebras, except the firft and the laft. It turns the neck obliquely backwards and a little to one fide. Below the pofterior part of the occiput are, The rectus capitis pofticus major. This mufcle arifes from the external part of the fpinous procefs of the fecond vertebra of the neck, afcends ob- liquely outwards^ and is inferted into the os occipkis. It 156 Mtifcles of the Neck, Be. [Book IX. It pulls the head backwards, and affifts a little in its rotation. The retlus capitis pofticus minor arifes from a little protuberance in the middle of the back part of the firft vertebra of the neck, and is inferted near the foramen magnum of the os occipitis. It aflifts in moving the head bdckwards. The obliquus capitis fuperior arifes from the tranf- verfe procefs of the nrft vertebra of the neck, and is inferted into the os occipitis. It draws the head back- wards.] The obliquus capitis inferior arifes from the fpinous procefs of the fecond vertebra of the neck, and is in- ferted into the tranfverfe procefs of the firft vertebra of the neck. This mufcle acts very powerfully in giving a rotatory motion to the head. On the fide of the neck are thefcalenus anticus, which arifes from the fourth, fifth, and fixth tranfverfe pro- cefies of the vertebrae of the neck, and is inferted into the upper part of the firft rib, The fcalenus medius, which proceeds from all the tranfverfe proceffes of the vertebras of the neck, ^nd is inferted into the upper and outer part of the firft rib. The fcalenus pofticus, which arifes from the fifth and fixth tranfverfe proceffes of the vertebras of the neck, and is inferred into the upper part of the fe- cond rib. The effect of all the fcaleni is to bend the neck to one fide, or, when the neck is fixed, to raife the ribs and dilate the thorax. There are a number of frrall mufcles fituated between the fpinous and tranfverfe proceffes of contiguous ver- tebras, fome of which approach fo nearly to the nature of Chap. 12.] Motkn of the Head. itf of tendons as to ferve merely as ligaments. The life of all thefe is to ftrengthen and credit the fpine. In the defcription which has been given of the muf- cles which ferve for the motion of the whole head, the reader cannot have failed to obferve, how much more numerous thofe are which are inferted into the back part ef the head, and pull it backwards, than thole which have the oppofite infertion and effect. The reafon of this is, that the center of gravity of the head does not fall on the condyls, on which it is fup- ported, but confiderably farther forward ; from which mechanifm it is evident that the mufcles which pull the head back muft be continually acted againft. Hence, when a perfon. falls afleep, or is affected with the palfy, and the mufcles ceafe to act, the head al- ways falls forwards. By the fpine being thus connected towards the poflerior part of the cranium, more fpace 'is allowed for the cavities of the mouth and fauces. Mufcles fituatedou the anterior part of the thorax. After having removed the common integuments of the thorax, we obferve a large mufcle, the pectoralis major, which rifes from the cartilaginous extremities of the fifth and fixth ribs, from almoft the whole length of the fte'rnum, and from near half the anterior part of the clavicle. Its fibres run towards the axilla, and it is inferted into the upper and inner part of the os humeri. Its effect is to move the arm forwards and obliquely upwards towards the fternum. Having removed this we come to another layer, which confifts of three mufcles. The fubclavius is a fmall mufcle which rifes from the firft rib, and is inferted into the inferior part of the clavicle. Its effect is to pull the clavicle downwards and forwards. The pectoralis minor arifes from the upper edge of the 158 Intercoftal Mufcles. [Book IX i the third, fourth, and fifth ribs, and is inferted into the coracoid procefs of the fcapula. Its ufe is to bring the fcapula downwards and forwards, or that being fixed* to pull the ribs upwards. The fefratus magnus originates from the nine fu- perior ribs, by an equal number of flefhy points, refembling the teeth of a faw, whence the term ferra- tus is derived. Faffing over two angles of the fcapula it is inferted into its bafe. Its effect is to move the fcapula forwards, or when the fcapula is forcibly raifed, to draw the ribs upwards. The mufcles which cover the ribs being removed* we obferve the fpace between the ribs filled up with double rows of mufcles, called the intercoftales externi and tnterni. The external arife from the inferior acute edge of each rib, and running obliquely forwards are inferted into the obtufe upper furface of the rib next below. The internal arife in the fame manner as the external, except that, contrary to them, they begin at the fternum, and run obliquely backwards. The two rows of intercoftals, therefore, decuffate each other like the ftrokes of the letter X. The effect of the con- traction of both feries is the fame, viz. that of bringing the ribs nearer to each other, and as each lower rib is more moveable than that above j to raife the ribs, dilate the thorax, and affift in infpiration. Certain portions, both of the external and internal intercoftals, are longer, and paffing over one rib are in-1 ferted into the next below it. The ribs are likewife raifed, and their pofterior articulations ftrengthened, by twelve fhort mufcles, which arife, from eleven of the tranfverfe proceffes of the dorfal vertebra, and the lowefl of thofe of the neck, and which are inferted intd the rib immediately below the tranfverfe procefs from which each of them rifes. Tt-efterno-coftalisarifes from the cartilago enfifor- mis, Chap, ii.] fbe Diaphragm* 159 mis, and is inferted into the lower edge of the cartikges of the third, fourth, and fifth ribs. Its effedt is to de- prefs thefe cartilages and the extremities of the ribs, to contract the cavity of the thorax, and therefore to afiifl in expiration. The moft important mufcle of the thorax, however, Hill remains to be confidered. The diaphragm is a broad and ftrong mufcle, which divides the cavity of the abdomen from that of the thorax. It is placed very obliquely between thefe two cavities, its anterior connection being much higher than its pofterior. Its middle part is forced up by the vifcera of the abdomen, fo as to form an arch. The diaphragm, at its anterior part, arifes from the upper and internal part of the cnfiform cartilage, and from the cartilages of the fixth, feventh, and all the inferior ribs. The mufcular por- tions arifing from all thefe points converge towards a common center, where they terminate in a broad trian- gular tendon. This being directed downwards and backwards is attached to a mufcular fubflance, which arifes by eight heads from the fecond, third, and fourtii lumbar vertebrae. There are feveral pafTages through the diaphragm, which muft not be pafled over in filence. Among the mufcular portion? which proceed frum the lumbar vertebras, are openings through which pafs the aorta, the thoracic duel:, the vena azygos, and the two great intercoftal nerves. The mufcular fibres, which proceed from the lumbar vertebrae, run ob- liquely upwards and forwards, and form in the middle two flefhy columns, which decuflate, and leave an oval fpace between them for the paflage of the cefophagus and eighth pair of nerves. Towards the right fide of the broad tendon, which forms the middle of the diaphragm, there is a large quadrangular open- ing, through which the vena cava pafles to arrive at the i6o Mnjcles of Expiration [Book IX, the heart. When the diaphragm contrails, .its con- cavity is IdTened, particularly on each fide, over which the lungs are placed, its center being firmly fixed from its connection with the mediaftinum. By the defcent, however, of its fides, it pufhes downwards and for- wards the abdominal vifcera, it lengthens, and of courfe enlarges, the cavity of the thorax, and is the principal mufcleof infpiration. The ribs are at the fame time raifed by the intercoftal mufcles, by which the thorax is made wider. The chief mufcles of expiration, on the other hand, are thofe which furround the abdomen. Thefe counteract the intercoftals, by pulling down the ribs, in which they are afliftcd by the ferrati, and op- pofe the diaphragm by the poftici inferiores prefling backwards and upwards the abdominal vifcera. By thefe mufcles refpiration is in general carried on. - In cafes, however, of laborious refpiration, whether from difeafe or violent exercife, other mufcles ar£ called into action ; infpiration is then promoted by the pectoral mufcles, the ferrati antici majores, the ferrati poftici pofteriores, and the fcaleni. That thefe mufcles may act with more advantage, perfons labouring under diffi- cult refpiration extend and fix the neck, and raife the fhoulders. In laborious expiration the quadrati lumbo- rum, facro-lumbales, and longifiimi dorfi, concur in pulling down the ribs. The elafticity of the cartilages of the ribs is alfo on all occafions an agent in expi* ration. The mufcles fituated on the anterior part of the ab- domen are five pair. On the middle of the anterior part of the abdomen, three of its mufcles, the two oblique and the tranfverfe, terminate in tendinous fubftance, v/hich forms an expanfion the whole way from the car- tilago enfiformis to the ofla pubis. This from its white appearance is calkd linea alba. The external layer is formed Chap. 12.] • Abdominal Mufcles. 161 formed by ;a mufcle, which from its fituation and the direction of its fibres is called the obliquus defcendens externus. This mufcle rifes by as many heads from eight or nine of the loweft ribs ; its notches" always mix with thofe of the ferratus major anticus, and generally adhere to the pectoralis major, intercoftals, and latirfi- mus dorfi. It proceeds obliquely downwards and for- wards, and is attached partly to 'the linea alba and partly to the fpine of the ileum. Its tendinous fub- ftance, which forms part of the linea alba, divides be- low into two columns, which leave between them a flit named the ring of the abdomen j of thefe columns the inferior is inferted into the os pubis of the fame fide, the fuperior decurTates its fellow, and paries over to be inferted into the os pubis of the other fide. That part of the external oblique mufcle, which is connected with the fpine of the ileum, is ftretched from the anterior fpinous procefs of that bone towards the os pubis, forming what is called Poupart's or Fallopius's liga- ment. This tendon is united with the ftrong tendi- nous expanfion of the thigh, called fafcia lata, which involves and meaths the mufcles of the thigh, and, pro- ceeding to the kg, performs there the fame office. The opening, called the ring of the abdomen, formed by the tendons of this mufcle, gives paffage to the fpermatic veffels in men, and the round ligaments of the uterus in women. The contents of the abdomen, getting through this opening, form the inguinal hernia* Under Poupart's ligament pafs the great veffHs of the thigh, and this is the feat of the crural or femoral her- nia.— This mufcle affifts in the exclufion of the fasces and urinej and in expiration, and bends the body for- wards. The fecond layer is formed by the obliquus afcen- dens internus. This mufcle ariies from the fpinous and tranfverfe procefles of the three uppermpft lumbar VOL, III. M vertebrae, i*>l Inguinal Hernia, &c. [Book IX. vertebrae, from the upper part of the facrum, and from the fpine of the ileuiny the whole length between the pofterior and fuperior anterior fpinous procefs. Pafiing obliquely upwards, it is inferted into the cartilaginous part of all the falfe ribs and the two loweft of the true, to the enfiform cartilage and to the fternum. At its anterior part it becomes tendinous, and dividing, re- ceives the rectus mufcle between its feparate portions. Its pofterior portion is connected with the tendon of the tranfverfalis mufcle, its anterior with the linea alba. At its loweft part it is inferted into the anterior part of the os pubis. Its ufe is to affift«the former, but k bends the trunk in the reverfe direction. The tranfverfalis has nearly the fame origins as the internal oblique. It is inferted into the cartilago enfi- formis above, and into the whole length of the linea alba, except at its lowermoft part. It fupports and comprefTes the abdominal vifcera. The rectus abdominis arifes from the cartilago enfi- formis and the cartilages of the three loweft true ribs. In its courfe downwards it paflcs through the fheath formed by the divifion of the tendon of the internal oblique, having the tendon of the external oblique without, and that of the tranfverfalis within. The rectus is generally divided ,by three tendinous in* terfections. Below it is connected to the ofla pubis, where they are joined to each other. The ufe of this mufcle is to comprefs the fore part, and more particu- larly the lower part of the abdomen. It alfo bends the trunk forwards, or raifes the pelvis towards the fter- num. By being furrounded by the tendons of other mufcleS, it is prevented from ftarting from its fituation. The pyramidales are a fhort pair of mufcles, fre- quently wanting ; they arife from the ofifa pubis, and are inferted into the linea alba about half way between them and the navel, They affift the rectus, The Chap. 12.] 'Epigaftric Region, &V. 163 The anterior part of the abdomen is diftingirilhed into feveral divifions, called regions, i. The epi- gaftric region, which reaches from the pit of the fto- mach to within three fingers breadth of the navel, and is bounded laterally by the hypocondria. 2. The umbilical region, which extends three fingers breadth above and below the navel, and is terminated laterally by the lumbar regions j and 3. Below the umbilical region is the hypogaftric, on each fide of which are the iliac regions. Still lower down is the region of the pubis. Within the cavity of the abdomen are fituated four pair of mufcles. The pfoas magnus arifes from the fide of the body and tranfverfe procefs of the loweft Vertebra of the back, and from thofe of all the ver- tebrae of the loins. Pafiing downwards through the pelvis it is inferted partly into the lefTer trochanter, and partly into that part t>f the os femoris a little below it. It railes the thigh forwards, or when the thigh is fixed, as in the pofture of {landing, it bends the trunk for- wards on the offa femoris. The pfoas parvus proceeds from the two upper vertebras of the loins, and fending ©fF a fmall long tendon, is inferted into the brim of the pelvis at the junction of the os ileum and pubis. It aflifts the pfoas magnus in bending the loins forwards* The iliacus internus arifes from the tranfverfe pro- cefs of the laft vertebra of the loins, from the inner edge of the fpine of the ileum, from the edge of that bone between its anterior fpinous procefs and the acetabulum, and from moft of the hollow, part of the ileum. It joins with the pfoas magnus, where it be- comes tendinous, is inferted along with it into the fmaller trochanter, and has the fame effect. The quadratus lumborum is feated further back- j it arifes from the pofterior part of the fpine of M 2 th$ 1 64 Mtifcles-of the Pelvis, '&c. [Book I3f. the ileum, and is inferted into the tranfverfe procefles of all the lumbar ve'rtebrse, into the laft rib near tjie fpine, and by a fmall tendon into the fide of the laft vertebra of the back. Its ufe is to draw the loins to one fide, or, when both aft, to bend the loins forwards towards the ileum. Within the pelvis are placed the obturator internus,. •which arifes from 'the internal circumference of the foramen thyroideum. Its tendon paries out of the pelvis, between the pofterior facro-ifchiatic ligament and the tuberofny of the os ifchium, and is inferted into the large pit at the root of the trochanter ma- jor. Its effect is to roll the os femoris obliquely out- wards. The coccygeus pafTes from the fpinous procefs of the ifchium to the bottom of the os facrum, and the whole length of the os coecygis.- By Its contraction the os coecygis is drawn forwards. Belonging to the anus are, The fphincter ani, which arifes from the fkin and fat which furround's the verge of the anus. The fibres are gradually collected into an oval form, and fur- round the extremity of the rectum, which they ferve to contract. The levator ani arifes from the os pubis, within the pelvis, and from the fpinous procefs of the ifchium. It is inferted into the fphincter ani, acceleratores uring?, and the point of the os coecygis, It furrounds the extremity of the re&um and the neck of the bladder, fo that joining with its fellow, they together very much referable the fhape of a funnel It fupports and draws the rectum. Chap. 13-] I l65 1 . CHAP. XIII. MUSCLES OF THE INFERIOR EXTREMITIES. Mufcles of the Thigh.— Of the Leg.— Of the foot and Toes. AS the two fides of the trunk of the body corre- fpond, a defcrip.tion of one fide is to be under- llood as applying equally to both. In the fame man- ner the parts of the extremities have their fellows on the oppofite fide. The mnfcles which belong to the thigh, and are fitn- .ated at the anterior part of the pelvis, are, • The pfoas magnus, 7 i j /• -L j _. .V \ already defcnbed. The iliacus mternuss } The pectinalis arifes from the upper and anterior part of the os pubis, immediately above the foramen thyroideum. It is inferted into the anterior and upper part of the Knea afpera of the os femoris, a little below the trochanter minor. Its ufe is to draw the thigh upwards and inwards, and to roll it in .fbme degree outwards. The triceps adductor femoris arifes by three diflinct heads from the ofia pubis, and is inferted into almoft the whole length of the linea afpera, into a ridge above the internal condyl of the os femoris and into the up- per part of that condyl. The ufe of this extenfive mufcle is, as the name exprefTes, to draw the thighs to- gether ; it alfo at the fame time tends to move them upwards and to roll the thigh outwards. The obturator externus furrounds the foramen thy- roideum, and alfo rifes from the membrane which fills yp that foramen, and from the adjacent parts of the os M ,3 pubis 1 66 Muffles of . [Book IX. pubis and ifchium. Its fibres converge tp a point, and pafTmg outwards around the back part of the neck of the os femoris, are inferted by a flrong tendon into the inner and back part of the trochanter major, adhering in their courfe to the capfular ligament of the thigh bone. Its ufe is to roll the thigh bone obliquely out- wards, and to prevent the capfular ligament from being pinched. The mufcles placed at the pofterior part of the pel- vis, and defigned for the motions of the lower extre- mity are, the gluteus maximus, which forms the ex- ternal layer, and arifes from the pofterior part of the Ipine of the ileum, from the whole pofterior furface of the os facrum, and from the pofterior facroifchiatic ligament j defcending obliquely, it pafles over tl\e trochanter major, is firmly connected to the tendinous expanfions of the tenfor vagina? femoris, and is inferted by a broad tendon into the upper and outer pare of the linea afpera. The effect of this mufcle is to draw the thigh backwards arid a little outwards. The gluteus medius forms another layer. It arifes from the anterior fuperior fpinous procefs and the dor- fum of the os ileum, and is inferted into the outer and pofterior part of the trochanter major. Its ufe is to draw the thigh outwards, and a little backwards, and to roll it, efpecially when it is bended. The third layer confifts of four mufcles. The gluteus minimus arifes from the outer furface of the os ileuiTi and the border of the great niche. It is inferted into the upper and anterior part of the great trochanter, and afiifts the former mufcle. The pyriformis arifes within the pelvis, from the an- terior part of the os facrum, thence becoming narrower, it paffes out of the pelvis along with the pofterior crural nerve, below the niche in the pofterior part of the os ileum. Chap. ij. II tie¥biglt&c. 167 ileum. It is inferted into a cavity at the root of the trochanter major. By its contraction it moves the thigh a little upwards, and rolls it outwards. The gemini confifts of two portions, one of which rifes from the outer furface of the fpine of the os if- chium, tfre other from the tuberofity of the os ifchium and pofterior facro-ifchiatic ligament. It is inferted into the fame part of the trochanter major with the pyriformis and obturator internus. This mufcle rolls the thigh outwards, and confines the tendon of the ob- turator internus.' The quadratus femoris arifes from the outfide of the tuberofity of the os ifchium, is inferted !into a ridge which pafles from one trochanter to the other, and rolls the thigh outwards. The mufcles feated on the thigh, and which move the leg, confift of two on the infide, one on the outfide, four before, and four behind. On the infide are, The fartorius, which arifes from the fuperior an- terior fpinous procefs of the ileum* This long mufcle, running downwards and a little inwards, is inferted into the inner fide of the tibia. It draws the legs obliquely inwards, fo as to bring the legs acrofs each other, for which reafon it is called the fartorius, or the taylor's mufcle. The gracilis arifes near the fymphyfis of the ofTa pubis, and is inferted with the fartorius into the inner part of the tibia. It afilfts the fortorius in bringing the legs acrofs, and, when they are a little bent, to concur in bending them further. On the outfide of the thigh is placed The tenfor vaginas femoris, which arifes from the external part of the anterior fuperior fpinous procels of the os ileum, It is inferted into the tendinous fafcia M 4 „ which 1 68 Mufcles of [Book IX, which covers and confines the mufcles of the thigh, Its ufe is to ftretch and fupport the fafcia, and alfo to roll the thigh fomewhat inwards. On the fore-part of the thigh are, The rectus, which arifes partly from the inferior and anterior fpinous procefs of the ileum, and partly from the dorfum of the ileum, a little above the acetabulum. Palling down the middle of the os femoris it is inferted into the patella, by the intervention of which its effect, that of extending the leg, is much increafed. The v'aftus externus arifes from the root of the tro- chanter major, and the outer edge of the linea afpera. through its whole length. It is inferted partly into the upper and outer part of the patella, and partly into the tendinous expanfion, which is" continued from the out- fide of the thigh to that of the leg. This mufcle aflifts the former in extending the leg. The vaftus internus arifes from the fore part of the os femoris, the root of the trochanter minor, -and inner edge of the linea afpera. It terminates partly in the tendinous aponeurofis of the leg, and is partly inferted into the inner and upper part of the patella. It alfo extends the leg. The crurasus arifes from the anterior part of the os femoris, between the two trochanters, but nearer the trochanter minor. It adheres firmly to the whole of the anterior part of the os femoris, is inferted into the middle of the patella, and afiifts in extending the leg. On the pofterior part of the thigh are placed The femitendinofus, which arifes from the tubcro- fity of the os ifchium, and is inferted into the infide of the ridge of the tibia a little below its tubercle. Its effect is to bend the leg and draw it inwards. The femimembranofus, which originates from the tuberofitv Chap. 13.] the Leg, &(. \ 169 tuberofity of the ifchium, and is inferted into the inner and back part of the head of the tibia. It bends the leg, and brings it directly backwards. The biceps flexor cruris arifes by two diftincl: heads, Of thefe the longer proceeds from the tuberofity of the ifchium, and the Ihorter from the linea afpera, a little below the termination of the gluteus maximus. The two heads join a little above the external condyl of the os femoris, and are inferted by a ftrong tendon into the head of the fibula, forming the external ham -firing. The internal is formed by the two preceding mufcles. The popliteus arifes from the lower and back part of the external condyl of the os femoris, it runs over the ligament which involves the joint, and is inferted into a ridge at the upper and internal edge of the tibia, a little below its head. It affifts in bending the leg, and prevents the capfular ligament from being pinched. The mufcles fituated on the leg, and which per- form the motions of the foot, are either extenfors or flexors of the foot, or extenfors and flexors of the toes in general. The extenfors of the foot are : the gaftrocnemius, which arifes by two heads, ope from each of the con- dyls of the os femoris. A little below the joint their flemy bellies unite in a middle tendon, and below the middle of the tibia it terminates in a broad tendon jof the following mufcle. The ibleus, or gaftrocnemius internus, alfo arifes by two heads; one from the upper and back .part of the head of the fibula, the other from the upper and pofterior part of the tibia. The fiefh of this mufcle, covered by the tendon of the gemellus, runs down nearly as far as the extremity of the tibia, a little above which the tendons pf this and of \he preceding mufcle unite, forming a ftrong 170 Mujcles of the Foot. [Book IX. ftrong cord called tendo achillis, which is inferted into the pofterior and projecting part of the os calcis. The diftance of the extremity of the os calcis from the aftragalus, which is the center, on which the motions of the foot are performed, gives thefe mufcles great power. Their effect is to extend the foot by bring- ing it more nearly into the direction of the tibia. When the foot, however, becomes the more fixed point, as in the erect pofture of the body, thefe two mufcles, by preffing the foot againft the ground, raife the body ; they are therefore very much employed in walking, running, and jumping, but particularly in afcending fteps, whence the fatigue felt in thefe mufcles which form the calves of the legs by a con- tinuance of that exercife. The plantaris arifes from the upper and back part of the external condyl of the os femoris, adhering in its defcent to the capfular ligament of the knee. Pafling under the gemellus, it fbon terminates in a thin tendon, which is the longeft in the body, and wh^ch is inferted into the infide of the back part of the os calcis. It co-operates with the former mufcle in ex- tending the foot, and alfo pulls the capfular ligament of the knee from between the, bones, and prevents it from being pinched. / The flexors of the foot are four, two of which be- long to the tibia and two to the fibula. The tibialis anticus proceeds from the upper and fore part of the tibia, and from the interoffeus liga- ment. Near the extremity of the tibia it fends ofPa round tendon, which paffes under the ligamentum tarfi annulare near the inner ankle. It is inferted into the infide of the os cuneiforme internum and the pofte- rior end of the metacarpal bone, which fuftains the great toe. The effect of this mufcle is to bend the foot* Chap. 13.] Calves of the Legs* their Ufe, &c. 171 foot, by drawing it upwards, and at the fame time ito turn it inwards. The tibialis pofticus proceeds from the upper part pf the tibia near its union with the fibula, then pafling through a perforation in the interofleous ligament, it continues its origin from the interofleous ligament, and from the upper half of the tibia, receiving alfo a few fibres from the fibula. It fends off a round ten- don, which paflcs in 3. groove behind the malleolus internus. It is inferred into the inner part of the os naviculare, and into the adjacent bones, at the internal and upper part of the foot. This mufcle alfo bends the foot, and turns it inwards. The two flexors which proceed from the fibula, are, The peroneus longus, which arifes from the fore- part of the head of the fibula or ftroney and alfo continues to receive fibres from the external part of this bone aimed as low as the ankle. Its tendon runs in a channel at the back part of the outer ankle, thence being reflected to the finuofity of the os calcis, it runs in a groove in the os cuboides, and pafling clofe to the bones in the fole of the foot, it is inferted chiefly into the metatarfal bone of the great toe. This mufcle moves the foot outwards and a little upwards. The peroneus brevis arifes from the outer and fore part of the fibula. Its tendon pafles behind the outer ankle, in which fituation it is retained by the fame .ligament as that of the laft mufcle. It is inferted into the root and external part of the metatarfal bone of the • little toe. This mufcle alfo moves the foot outwards and a little upwards. The common extenfors of the toes are, The extenfor longus digitqrum pedis, which arifes from the upper, outer, and fore part of the tibia, yiterofleous 172 Mujdes tf tbe Toes. [Book IX. interofleous ligament, and inner edge of the fibula. It divides into four tendons under the, ligamentum tarfi annulare. It is inferted by four flat tendons into . the roots of the firft joints of the four fmall toes. Its ufe is to extend all the joints of thefe toes. A por- tion of this mufcle is inferted into the metatarfal bone of the little toe, affifts in bending the foot, and is called the peroneus tertius. The extenfor brevis digitorum pedis arifes from the fore and upper part of the os calcis, is inferted into the tendinous expanfion at the upper part of the foot, and extends the toes. The common flexors of the toes are, The flexor brevis digitorum pedis, which arifes from the lower part of the os calcis. Its thick flefhy belly foon divides into four tendons, which, after being pierced by thofe of the following mufcle, are inferted into the fecond phalanx of the four fmall toes. This mufcle bends the fecond joint of thefe toes. The flexor longus digitorum pedis arifes from the upper and back part of the tibia, fome diftance below its head. In its courfe downwards it is increafed by flefhy fibres from the inner edge of the tibia, and by means of tendinous fibres is connected to the outer edge of that bone. Faffing under two annular liga- ments, which retain its tendon in its proper fituation, it is received into a finuojity at the infide of the os calcis, and about the middle of the fole of the foot divides into four tendons, which perforate thofe of die flexor brevis, and are inferted into the extremity of the laft joint of the four fmall toes. Its ufe is to bend the Jaft joint of the toes. This mufcle receives, in the fole of the foot, another, which arifes from the infide of the os calcis, and which increaics its ftrength. .The £hap. 13.] tfsndinous Expanfon, &c. 17 j The lumbricales pedis are four fmall mufcles in the fole of the foot, fo called from their refemblanee in fize and appearance to earth-worms : they arife from the four tendons of the flexor digitorum longus, and are inferted into the infide of the firft joint of the four fmall toes. Thefe mufcles render the flexion of the toes more extenfive, and draw them inwards. The mufcles fituated chiefly on the foot are thofc de- figned for the motions of each of the toes in particular. To the great toe belong five mufcles. Of thefe, one extends 'it, two bend it, one draws it outwards, and another inwards. The little toe, befides the common flexors and ex- tenfors, has two mufcles proper to itfelf. One of thefe draws it outwards, and the other contributes to its flexion. Between the metatarfal bones are alfo feated feven mufcles, called the interoflei interni et externi. The internal interoflei are three in number ; their ufe is to draw the three fmaller toes towards the great toe. The external interoflei are four; of thefe, the firft ferves to move the fore-toe towards the great-toe ; the other three draw the three toes next the great toe outwards. All the interoflei aflift in extending the toes. The tranfverfalis pedis arifes from the under part of the anterior extremity of the metatarfal bone of the great toe, and terminates at that of the metatarfal bone of the little toe. By the contraftion of this mufcle the great and little toes are brought nearer. The mufcles fituated in the foot are covered and protected by a ftrong tendinous expanfion, which pafies from the os calcis to the firft joints of all the toes. t 174 1 C it A p. XIV. MUSCLES OF THE SUPERIOR EXTREMITIES. Stafitlat Mufcles. — Mufcles of the Fore-arm. — Of the Hand. — Of the Fingers. THE pe&oralis major and latifiimus dorfi havfe already been defcribed. The mufcles which are feated on the fcapula, and which are inferred into the os humeri, are, The fuprafpinatus, which arifes, as its name ex- preiTes, from that part of the fcapula which is above its fpine j it pafles under the acromion, adhering to the capfular ligament of the os humeri, and is inferted into the large tuberofity on the head of that bone. Its ufe is to raife the arm upwards, and to draw the cap- fular ligament from between the bones, fo that it may not be hurt by compreffion. The infrafpinatus, which originates from all. that part of the bafe of the fcapula that is between its fpine and inferior angle; and alfo from the fpine as far as the cervix fcapula. Its tendon, running forwards, is conne&ed with the capfular ligament, and terminates in the middle and upper part of the protuberance on the head of the os humeri. This mufcle rolls the humerus outwards, fupports the arm when raifed, and alfo afilfts in raifing it, and pulls tho ligament from be- tween the bones. The teres minor arifes from the inferior coda of the fcapula, and is inferted into the back part of the tu- berofity on the head of the os humeri. Its ufe is to roll the humerus outwards and draw it backwards, and by Chap. 14.] Scapular Mufdes. ijj by its connexion with the capfular ligament of the os humeri, to draw it from berween the bones. The teres major arifes from the inferior angle and inferior coda of the fcapula -, its flefhy fibres are con- tinued over part of the infrafpinatus mufcle, to which they firmly adhere. It is inferted, by a broad and thin tendon, along with the latifiimus dorfi, into the ridge at the inner fide of the groove for lodging the tendon of the long head of the biceps. Its effecT: is to roll die humerus inwards, and draw it backwards and downwards. The deltoides arifes from the clavicle, proceflus acromion, and the fpine of the fcapula ; from thefe origins its fafciculi converge, forming a covering to the anterior part of the joint of the os humeri. It is in- ferted into a rough protuberance in the outer fide of the os humeri. The chief effe6t of this mufcle is to raife the arm ; but from the different direction of its fibres, it may alfo move it backwards or forwards. The coraco-brachialis arifes from the fore part of the coracoid procefs of the fcapula, is inferted into the middle and inner fide of the os humeri, and moves the arm upwards and forwards. The fubfcapularis arifes from the whole internal fur- face of the fcapula ; after being attached to the cap- fular ligament, it is inferted into the upper part of the fmall internal protuberance at the head of the os humeri. It rolls the os humeri inwards, draws it to the fide of the body, and draws the capfular ligament from be- tween the bones. The mufcles iituated on the os humeri, and which move the fore-arm, are only four; two being placed before for the flexion of the joint, and two behind for its extenfion. Thofe placed before are, The biceps flexor cubid, which confifts of two heads, which unite about the middle of the os humeri. Of thefe t76 Mufcles of the Fore-arm, £sV. [Book IXk thefe the fhorter rifes from the coracoid procefs of the fcapula; the longer and outermoft begins from the upper edge of the glenoid cavity of the fcapula, paries over the head of the os humeri within the joint, and in its defcent without the joint is inclofed, by a mem- branous ligament, in a groove near the head of the os humeri. This mufcle is inferted, by a ftrong roundifh tendon, into the tubercle on the upper end of the radius internally. Its effects are to bend the fore- arm, and to turn the radius outwards, and fo bring the palm of the hand uppermofl. Part of the tendon proceeding from this mufcle is alfo fpent in a tendinous eyxpanfion, wh'ch covers all the mufcles at the mfide of the fore arm, and joins with another tendinous membrane, which is fent off behind from the triceps extenfor cu- biti. The ufe of thefe expanfions, as in other parts of the body, is to confine the motions of the mufcles, to protect them, and to give origin to a number of fibres. The brachialis interims arifes from the os humeri at each fide of the infertion of the tendon of the deltoides* Being clofely applied to the inferior and inner part of the os humeri, it runs over the joint, is firmly attached to the ligament, and is inferred into the coronoid pro- cefs of the ulna. It aiT:fts the former mufcle in bend*, ing the fore-arm. Behind are The triceps extenfor cubiti, which confifts of three heads'; of thefe one proceeds from the inferior cofta of the fcapula, another from the upper and outer part of the os humeri, and the third from the back part of that bone. Thefe three heads, when united, form a large mufcle, which is clofely applied to the pofterior part of. the humerus, from which they receive .fome 6 mufcular Chap. 14.3 Mufcles of tie Fore-arm, &c. 177 taufcular fibres. This mufcle is fixed to the upper and outer part of the olecfanon of the ulna. The anconeus arifes from the external condyle of the os hurticri, and is infeirted into a ridge on the outer and pofterior edge of the ulna. It affifts in extending the fore-arm. The mufcles fittiated on the fore-arm may be di- vided into four orders: I. Flexors and extenfors of the whole hand. 2. Flexors and extenfors of the fin- gers. 3. Supinators and pronators, or thofe which roll the radius on the ulna. 4* Flexors and extenfors of the thumb and fore^-finger. The firft order confifts of three flexors and three ex- tenfors* The flexors are, The palmaris longus> which arifes from the inner condyle of the os humeri, and is inferted partly into the annular ligament, which confines the tendons feated in the wrift, and partly into the tendinous expanfion, which covers the palm of the hand. This mufcle bends the wrift and ftretches this membrane. The palmaris brevis, which originates from the an- nular ligament and tendinous expanfion on the palm of the hand, and is inferted into the os pififorme, and the fkin covering the abduclor minimi digici. It affifl;s in contracting the palm of the hand* This fmall muf- cle is commonly confidered as belonging to the former. The flexor carpi radialis proceeds frorr the inner condyle of the os humeri, and is inferted into the me- tacarpal bone of the fore- finger. It bends the hand and afiifts in its pronation, that is, in turning the palm downwards. The flexor carpi ulnaris arifes alfo from the internal condyle of the os humeri, and alfo from the outer fide of the olecranon. I? is inferted into the os pififorme, and afllfts in bending the wrift. VOL. III. N The i;8 M-ufcles of the "[Book IX. The extenfors of the whole hand are, The extenfor carpi radialis longior, which arifes from the lower part of the external ridge of the os hu- meri, above its external condyle. Ic is inferted into the upper part of the metacarpal bone, which fupports the fore-finger. Its efFeft is to extend the writ! and draw the hand backwards. The extenfor carpi radialis brevior arifes from the outer part of the external condyle of the humerus, and from the ligament which connects the radius to it. It is inferted into the upper part of the metacarpal bone of the middle finger, and extends the wrift. The extenfor carpi i?lnaris arifes from the external condyle oftheos humeri, and alfo receives an acceflion of fibres in its progrefs from the ulna. Its round ten- don is confined by a membranous Iheath in a groove, which is fituated at the extremity of the ulna. It is inferted into the upper part of the metacarpal bone of the little finger, and affifts in extending the wrift. The flexors and extenlors of the four fingers are, The flexor fublimis perforatus, which arifes from the internal condyle of the os humeri, the inner edge of the coronoid procefs of the ulna, and the upper and anterior part of the radius. It fends off four tendons before it pafies under the ligament of the wrift, which being divided for the pafiage of the tendons of the following mufcle, are inferted into the anterior and up- per part of the fecond bone of each finger. It bends the fecond joints of the fingers. The flexor profundus perforans, which originate! from the upper part of the ulna, and from a confiderable part of the interofleous ligament. It divides into four tendons, which pafs through the ilits in the tendons of the preceding mufcle, and are inferted into the up- 9 PW Chap. 14*] Hand) Fingers, &c, ijg per part of the laft bone of the four fingers. Its ufe is to bend the laft joint of the fingers. The lurnbricales arife from the four tendons of the preceding mufcle> and are inferted into the outer fides 'of the broad tendons of the interoflei mufcles. They increafe the flexion of the fingers. The extenfor digitorum communis arifes from the •outer tondyle of the os humeri, and is inferted into the polterior part of all the fingers by a tendinous expan* fion. It extends all the fingers. The mufcles, which roll the radius on the ulna> are, The fupinator radii longus, which arifes from the external ridge of the os humeri above the external cond.yle. It is inferted into the outer fide of the infe- rior extremity of the radius. Its effect is to roll the radius outwards, and confequently to turn the palm of the hand upwards. The fupinator radii brevis, which arifes from the external condyle of the os humeri» and pofterior fur- face and outer edge of the ulna. It is inferted into the head, neck, and tubercle of the radius. It rolls the radius outwards, and turns the pairn of the hand upwards. The pronator radii teres, which originates from the -internal condyle of the os humeri and coronoid pro- cefs of the ulna. It is inferted into the pofterior part of the radius, about the rhiddle of that b-*ne. Its effecl: is to roll the radius, with the hand, inwards, and coq- fequendy to turn the back of the/ hand upwards, or to lay the hand prone. The pronator radii quadratus arifes from the inner and lower part of the ulna. Its fibres, running tranf- verfely, are inferted into the anterior part of the radius oppofice to their origin. For the motion of the thumb are placed in the fore -arm, N 2 The i So Mujcles of tie [Book IX. The flexor longus pollicis manus, which originates from the upper and fore part of the radius j its tendon paiTes under the ligament of the wrift, and isinferted into the laft joint of the thumb, which it ferves to bend. The extenfor oflis metacarpi pollicis manus, which arifes from the middle and pofterior part of the ulna, from the middle and pofterior part of the radius, and from the interofleous ligament. It is inferted into the os trapezium and upper back part of the metacarpal bone of the thumb. Ics effect is to extend the meta- carpal bone of the thumb outwardly. The extenfor primi internodit arifes from the pofterior part of the ulna, and from the interofleous ligament. It is inferred into the pofterior part of the firft bone of the thumb, which it extends obliquely outwards. The extenfor fecimdi internodii, arifes from the- middle and back part of the ulna, and from the inter- ofTeous ligament, and is inferted into the laft bone of the thumb, which it extends obliquely backwards. To the fore-finger brlongs The indicatbr, which begins from the pofterior part of the -ulna, about the middle of that bone. Its ten- don, accompanying that of the extenfor digitorum communis, which belongs to the fame finger, they arc inferted together into its upper part. Its effect is to extend the fore-finger, whence its name of indicator, as that is the finger with which we ufually point at any object of attention. The mufcles feated in the hand may be divided into thofe of the thumb and thofe of the fore and little fingers. The flexor brevis pollicis manus. arifes from the os trapezoides, annular ligament, os magnum, and os un- ciforme, and is inferted into the fecond joint of the thumb, which it ferves to bend. The Chap. 14.] Tlandy Finger ', &V. 181 The flexor ofiis metacarpi pollicis, or opponens pollicis, arifes from the os trapezium and ligamentum carpi annulare. It is inferted into the under and an- terior part of the firft bone of the thumb. Its effect is to bring the thumb inwards, fo as to place it in oppo- fition to the fingers. The abductor pollicis rnanus commences from the ligamentum carpi anmilare and from the os trapezium, and is inferred into the outer fide of the root of the firft bone of the thumb. Its ufe is to draw the thumb from the fingers. The adductor pollicis manus arifes from the me*- tacarpal bone which fuftains the middle finger, and is inferted into the inner part of the root of the firft bone of the thumb. This mufcle pulls the thumb towards the fingers. The thumb has, therefore, in all, eight mufcles, four feated in the fore-arm and four in the hand. Of the whole eight, three are flexors, three extenfors, one is an abductor, the other an adductor. One mufcle, the indicator, proper to the fore-finger, and feated in the fore-arm, has been already defcribed ; another mufcle proper to this finger is feated in the hand j it is called The abdudor indicis manus, and arifes from the inner fide of the firft bone of the thumb and from the os trapezium, and is inferted into the r"irft bone of the fore-finger. It ferves to bring the fore-finger towards the thumb. To the little finger belong The abductor minimi digiti, which arifes from the os pififorme and the adjacent part of the annu- lar ligament. It is inferted into the fide of the firfl bone of the little finger, which it draws from the reft. N 3 The i Si Hand, Fibers, &c. [Book IX . The adductor metacarpi minimi digit! manus, which arifes from the os unciforme and the adjacent part of the annular ligament; it is inferred into the anterior part of the metaearpal bone of the little finger, which it draws towards the reft. The flexor parvus minimi digiti arifes from the o& unciforme, and from the ligament of the wrift near it, and is inferted into the firft bone of the little finger. It bends the little finger, and aflifts die ad- du&or. Between the metacarpal bones there are four in- ternal and three external mufcles, named interoffei. They are inferted into the roots of the fingers. The interoffei interni extend the fingers, and move them towards the thumb, except the third, which draws the middle finger from the thumb. The interoflei externi alfo extend the fingers j but the firft draws the middle finger inwards, the fecond draws it outwards, and the third draws the ring-finger inwards. The figure in Plate IV. reprefents the firft layer of mufcles fituated on the anterior part of the whole body, immediately under the common integuments* and tendinous fafcias. MUSCLES fituated on the HEAD and NECK. «/The anterior flefhy belly* of the occipito-frontalis fituated on the os frontis. Above a, the tendinous aponeurofis of the occipito- frontalis, covering the upper part of the parietal bones. &} Attollens aurem. „ Under it the tendinous aponeurofis covering the temporal mufcle. Anterior auris between c and the car, c3 Orbicularis palpebrarum. Its C&ap. 14.] Explanation of tie Mufcular Plates. 183 Its tendon is feen at the inner canthus, fixed to the nafal procefs of the fuperior maxillary bone. Levator labii fuperioris aheque nafi. Seen divided fnto two portions running down along the fide of the nofe ; and on the outfide ' of it, the levator anguli oris. Next this, the .Zygomaticus minor. Farther outwards, Zygomaticus major. On the ala and tip of the nofe, the Compreffor naris. dy DeprefTor anguli oris. And beneath it, a portion of the depreflbr labii inferioris. gy Orbicularis oris. /, Platyfma-myoides. Behind /, the fterno-cleido-mafloideus is feen through the platyfma-myoides. TRUNK. *, Pe&oralis major. The upper part of it is covered by the origin of the platyfma-myoides. by Serratus magnus. The other portions refemble this. Cy Latiffimus dorfi. dy Obliquus externus defcendens. Cy Linea femilunaris. /, Linea alba. Below/, the umbilicus. Between e and /, the re&us abdominis ; and, at the inferior part of the linea alba, oppofite to £, the pyramidales appear through the tendons of the oblique mufcles. N 4 g> Ring 1 84 Explanation of the [Book £, Ring of the external oblique mufcle j with the fper- matic chord, pafling through it, and covered by the cremafter mufcle. SUPERIOR EXTREMITY. 0, Deltoides. Above the clavicle, a portion of the trapezius is feen; ly Biceps flexor cubiti. At the bending of the arm is feen its tendon going towards the radius, and the part* from which the tendinous aponeurofis that covers the fore-arm, is cut off. On the infide of the biceps, part of the triceps ex- tenfor cubiti j and on the outfide, part of the? brachialis internus. r, Supinator radii longus. • d, Pronator teres. ey Palmaris longus, /, Palmaris brevis. On the palm of the hand, the aponeurofis palmaris, is feen extended from the annular ligament at the wrift, to the roots of the metacarpal bones of the four fingers. g. Flexor carpi radialis. b, Part of the flexor fublimis perfbratus. 7, Infertion of the flexor carpi ulnaris. k, Abdudor pollicis. INFERIOR EXTREMITY. Qy Tenfor vagina femoris, the vagina or tendinous fafcia being cut off. On the outfide of it a portion of the glutasus maximus. £, Part of the iliacus internus. On the inlide of it, between It aiftd c> part of the pfoas magnus. c, Pec^inalis, dy Triceps Chap. I4-] Mufcukr Plates* 185 dy Triceps longus. fy Gracilis. fy Sartorius. g, Re&us cruris. Its tendon is feen inferted into the patella, from which a ftrong tendon is fent to be fixed to the tubercle of the tibia. l>y Vaftus externus. /', Vaftus internus. ky Tibialis antic us. /, Peroneus longus. On the outfide of it, a portion of the folasus. mt Extenfor longus digitorum pedis, with the pero- nseus tertius, and extenfor proprius pojlicis pedis. nt Gaftrocnemius externus, or gemellus. 0y Soleus. ^>, Ligamentum tarfi annulare. £, Abdu6tor pollicis pedis. The figure in Plate V. reprefents the fecond layer of mufcles on the anterior part of the whole body. MUSCLES fituated on the HEAD and NECK. a, Corrugator fupercilii. bt Temporalis. c, Maficter, dy Levator anguli oris. /, Buccinator. f9 Orbicularis oris. Oppofite to the right ala nafi, the portion of this mufcle, which Albinus names Nafalis labii fuperioris. gy Depreffor labii inferioris. £, Sterno-cleido-maftoideus, which is Seen below, arifmg from the fternum and clavicle, by two heads. * i Sterno- 1 8.6 Explanation of the [Book i, Sterno-hyoideus. On the outfide of it, the Omo-hyoideus. Further out, a portion of the Hyo-thyroideus. kf Levator fcapulas. TRUNK. a, Subclavius. I, Pectoralis minor. c, Serratus magnus. d> Reftus abdominis, divided into feveral flefhy por- tions by its tendinous interfections. e, Pyramidalis. /, Obliquus afcendens internus. g, Spermatic chord, with the origin of the cremafter mufcle. SUPERIOR EXTREMITY. a, Biceps flexor cubiti. b) Short head of the biceps. Beneath the upper part of in, a portion of the cora- cobrachialis. Beneath the under part, a portion of the brachialis internus. cy Long head of the biceps. At the bending of the arm, the tendon of the biceps, and the place where the tendinous aponeurofis was cut from it, are feen. dy Extenfof carpi radialis longior. Beneath it a portion of the Extenfor carpi radialis brevior. et Flexor fublimis perforatus. ft Infertion of the extenfor carpi ulnaris. ft Extenfors of the thumb. b, Op- Chap. 1 4-] Mujcular Plates. 187 b, Opponens pollicis. On the infide of it, a portion of the Flexor pollicis brevis. iy Tendon of the flexor longus pollicis manus, after paffing through the flexor brevis pollicis manus, k, Abductor minimi digiti manus. - /, Flexor parvus minimi digiti manus. #&, Ligamentum carpi annulare. INFERIOR EXTREMITY. ay lliacus internus. Between a and b, part of the pfoas magnus. l>3 Pectinalis. c> Triceps longus. 4, Gracilis. f, Rectus cruris cut off near its origin. f> Tendon of the re&us cruris cut ofFabove the patella, from which a ftrong tendon is fent to be inferted into a tubercle of the tibia. g, Portion of thegluteus medius. On the infide of it, part of the gluteus minimus.. I, Vaftus internus. /, Vaftus externus. kt Crur^eus. /, Infertionof the biceps flexor .cruris into the fibula. wt Tendons of the gracilis and iemitendinofus inferted into the tibia. #, Soleus. Oj Peronseus longus, p, Extenfor longus digitorum, with the peronaeus ter- tius on the outfide, and extenfor pollicis proprius on the infide. q, Soleus. r, Flexor longus digitorum. t Tendons iSS Explanation of the [Book I XT. fy Tendons of the tibialis pofticus and flexor longus digitomm pedis. ty Flexor brevis digitorum pedis. The figure in Plate VI. reprefents the third layer of mufcles, with fome of the ligaments, cartilages, and naked bones on the anterior part of th@ whole body. a, DeprefTor labii fuperioris akeque nafi. ly Orbicularis oris, after mod of the mufcles, which are fixed to it, and affift to form it, have been taken away. f, Buccinator. Above Cy part of the pterygoidasus externus is feen pafiing behind the coronoid procefs of the lower jaw. dy Levator labii inferioris. e, Sterno-thyroidasus. Immediately above, and feemingly the continua~ tion of it, the Hyo-thyroidasus, /, Scalenus anticus. Contiguous to it, on the infide, the Scalenus medius. Above it, a portion of the Trachelo maftoidseus. Between the fcalenus anttcus, and {lernQ-thy- roideus, and hyo-thyroidseus, the Redus capitis anterius major, and Longus colli. TRUNK. Gy Third row of external intercoftal mufcles. The reft appear in the fame manner between die other ribs. *, Third Chap, 14.] Mufcular Plates. i$f bt Third row of internal intercoftal mufcIeS. The reft appear between the other ribs. cy Tranfverfalis abdominis. dt The place from which the inferior part of the tendon of the tranfverfalis, that pafies before the rectus and pyramidalis mufcles, is cut off. Between thefe portions of each fide, the peritonaeum is laid bare, and the ligaments of the bladder, which were formerly the umbilical arteries and urachus. Between this portion and the os pubis, the fpermatic chord is feen cut. et The inferior edge of the upper part of the tendon of the tranfverfaiis, which pafles behind the rectus, and immediately adheres to the peritonaeum. /, The anterior lamella of the internal oblique, which joined the tendon of the external to pafs orer the rectus. Between / and g, the pofterior lamella of the internal oblique, joining with the tendon of the tranfver- faiis, to pafs behind the rectus. £, The place at the linea alba, from which .the tendon of the external oblique, and anterior lamella of the internal, were cut off. At£, Umbilicus. SUPERIOR EXTREMITY. «, Subfcapularis. b, Teres minor. c, Coraco-brachialis. The part from which the (hort head of the biceps flexor cubiti was cut off from it, is feen at its up* per end. d> Brachialis interims. e3 Brachialis externus, or third head of the triceps. f, Extenfor 19$ Explanation of tat [Book IX* /, Extenfor carpi- radialis longior, and with it the ex* tenfor carpi radialis brevior. Both thefe are diftin&ly feen in the right hand. Between the tendon of the brachialis internus and extenfor radialis, the Supinator radii brevis is feen. & Flexor longus pollicis manus, with the flemy por- tion of it which arifes from the internal condyle of the os humeri. b, Flexor profundus perforans, which fplits into four tendons, which pafs under the ligamentum carpi annulare. i, Pronator quadratus. k, Adductor minimi digit! manus. /, One of the lumbricales. The other three appear in the fame manner, along the tendons of the flexor profundus. Behind thefe, the internal interoffei are feen. INFERIOR EXTREMITY. a, Glutseus minimus. £, Iliacus internus, On the infide of it, between I and r, the pfoas mag- nus. r, Obturator externus. d* Addudor brevis femoris. e, Adductor magnus femoris. /, Gracilis ; which is Seen inferted into the infide of the head of ths tibia. gy The fliort head of the biceps flexor cruris. b, Peroneus longus. ij Peroneus brevis. Between thefe two peronei and tibia, the tibialisi pofticus is feen. *, Tendon Chapv 1 4.] Mufcular Pktes. 1 9.1 ' k, Tendon of the tibialis pofticus, covering the tendon, of the flexor longus digitorum pedis. /, Extenfor brevis digitorum pedis. The figure in Plate VII. reprefents a back view of the mufcles, which are immediately fituated below the common integuments. -HEAD and NECK. it, Part of the occipito-frontalis mufcle, with its apo- neurofis. b, Attollens aurem. c, Anterior auris. d> Retrahentes auris. TRUNK.. a, Trapezius, or cucularis. bi Its tendinous edge joining with its fellow in the nape of the neck, which is called ligamentum nuch c. Part of the tenfor vaginae femoris. ^.Vaftus externus. ey The long head of the biceps flexor cruris 5 And beneath it, fy Part of the ihort head< j £, Semifendinoius : And beneath it, on each fide, A portion of the femimembranofus in feen* b. Gracilis. On the outfide of it, A portion of the abduftor magnus is feeri* /, Afmall pirtof the vailus internus. ky Gaftrocnemius externus, or gemellus } And Chap. 14.] Miijcular Plates. 193 And within its outer head, A portion of the plantaris. /, Solasus or gaftrocnemius internus. m> Tendo Achillis, with the piantaris. w, Peroneus longus. o-y Peroneus brevis ; between it and the tendo Achillis, a portion of the flexor longus digitorum pedis. ^, Tendons of the extenfor longus digitorum pedis, with the peroneus tertius, patting tinder the li- gamentufn tarfi anntilare ; and the flexor brevis digitorum pedis is feen beneath them. f, Abduftor minimi digiti pedis j and above it the ten- dons of the peroneus longus and brevis, patting under their own proper ligaments. The figure in Plate VIII. r'eprefents the fecorid layer of the mufcles on the back-part of the body. HEAD and NECK. <*, TTemporalis; its tendon is feen patting below the zygoma. #, Matteter. c, Splenius capitis et colli. ^, Portion of the complexus. €) Levator fcapulse, or the rnufculus patientise, T'R u N K. a, Rhomboides major; , Serratus 194 Explanation of the [Book IX. h, Serratus magnus. ;, The broad tendon, by which the latifllmus dorfi be- gins, and from which the tendon of the ferratus pofticus inferior is infeparable. ky Part of the obliquus internus afcendens abdominis. Jj The fphinfter ani, fixed to the point of the os coc- cygis ; at the fide of which the coccygaeus, and a portion of the levator ani, are feen, &c. SUPERIOR EXTREMITY. a, Supra-fpinatus. b} Infra-fpinatus. Cj Teres minor. dy Teres major. e, Triceps extenfor cubiti. /, Its head called longus. gy The brevis: And, by A fmall portion of the third head, named Iracbian* externus. i, The tendon of the triceps, inferted into the olecra- non. k, Part of the brachialis internns. /, Anconsus, which feems to be continued from that part of the brachialis externus immediately above it. my Extenfor carpi radialis longior ; and beneath it, the brevior : both are feen at the wrift, inferted into the metacarpal bones of the fore and middle fingers. », Flexor carpi ulnaris. c, Part of the fupinator radii brevis. ^>, Extenfor offis metacarpi pollicis manus. ^, Extenfor primi internodii pollicis manus. r, Extenfot fecundi internodii pollicis maous, /, Indi- Chap. 14.] faufcular Plates. 195 J~y Indicator, inferted into the root of the firft joint of the fore -finger. i, One of the three external intefofTei rnanus. The other, two are diftinctly feen without letters. #, One of the tendons of the extenfors of the fingers cut; and the fame is feen in each of the other three fingers, joining with the tendons and aponeurofes of the interoflei and lurribricales, and fpread upon the back of the fingers. N. B. On the right hand, part of the flexors of the fingers, the abduclor pollicis and minimi digitij are feen* INFERIOR EXTREMITY*, *?, Grlutasus medius* b, Pyriformis. r, The two mufcles called gemim> between which the tendon and fiefhy belly of the obturator internus pafles over the tuberofity of the os ifchium, are feen within the pelvis, partly covered by the coo cygscus and levator ani. ^,'Qiiadratus femons. «?, V aft us externus. /, /, Parts of the triceps tnagnus. g, Long head of the triceps flexor crur'is, and beneath it part of the fhort head is feen. ht Semitendinofds, and beneath it parts of the femi- membranofus are feen on each fide of it. i, Gracilis. k, A fmall portion of the vaftus internus. /, Poplitasus. m, The flefhy belly of the plantans j and its long flen- der tendon is feen pafling over the infide of the folseus. 196 Explanation of the [Book IX, n, Solseus. 0, The place where the tendon of the gemellus was cut offj but the flefh of the folseus runs farther down. f, Tendo Achillis, with the plantaris. q, Peroneus longus> paffing at the outer ancle to the fole of the foots beneath it, the peroneus brevis to the root of the metatarfal bone of the little toe ; and, between it and the tendo Achillis, a portion of the flexor longus digitorum pedis. r, Tendons of the extenfor longus digitorum pedis, with the peroneus tertius ; and beneath thefe, the extenfor brevis digitorum pedis. Jj Flexor brevis minimi digiti pedis. The figure in Plate IX. reprefents the third layer of mufcles on the poflerior part of the body, with fome of the ligaments and naked bones. MUSCLES on the HEAD and NECK. a, Part of the buccinator. by Complexus. c, Trachelo-maftoideus j on the outfidc of it, the tranfverfalis colii. t d3 Scalenus medius. e, Scalenus pofticus. TRUNK. a, Spinalis dorfi j and beneath it, the multifidus fpinas. by Longiffinaus dorfi, which fends off a flefliy flip to the tfacheio-maftoidasus. c, Sacro lumbalis, with the cervicalis'defcendens fent cff from it along the fide of the neck, and -out- fide of the tranfverfalis colli. d, Semi-r Chap. 14.] Mufcular Plates, 197 dy Semifpinalis dorfi. e, Tranfverfalis abdominis. N. B. The fpaces between the fpinous precedes of the vertebras have mufcular fafciculi between them, particularly thofe of the neck ; and are named interfpinales c olli, dorfiy and lumbar wn ; but thofe of the back ^feern to be tendinous and liga* mentous. SUPERIOR EXTREMITY, a, Teres major. by Part of the coraco-brachialis, £, Part of the brachialis internus. dy The third head of the triceps extenfor cubiti, called brachialis externiisy after the longus and brevis have been cur off. e, fextenfor radialis longior, f> Extenfor radialis brevior. g> Part of the flexor profundus perforans. by Supinator radii brevis. i, Part of the adductor pollicis manus. ky One of the three external interofiei ; the other two may be eafily diftinguiflied without letters. /, - Tendons of the extenfors of the fingers, joining; with thofe of the lumbricales and interoflei, which form a tendinous expanfion on the back. of the four fingers. N. B. On the right hand, part of the flexors of the ringers and thumb, part of the adduftor pol- licis, and the whole of the adductor minimi digiti, are feen. Oj 198 Explanation, (&. [Book IX. INFERIOR EXTREMITY. a, Glutasus minimus. b3 Obturator internes j its flefhy belly is feen withiii the pelvis. Beneath b, the tendon of the obturator externns. f, Semimembranofus. d, The fhort head of the biceps flexor cruris. e, Triceps magnus. /, Gracilis. In the ham, the origins of the two heads of the gaftrocnemius externus and plantaris, are feen. g, Popljka&us. by Tibialis pofticus. i, Flexor longus digitorum pedis. k, Flexor pollicis longus. /, Peroneus longus, running down to be inferted irita the rpetatarfal bone of but are placed behind it, are the kidneys, the, ureters, the receptacle of the chyle, the aorta, and the vena c.iva. The upper part of the bladder is involved in the pe- ritoneum, the lower is placed without it. The peritoneum is to be confidcred as a membrane forming an internal covering to the parts which are the boundaries of the abdomen, and at the fame time doubled back on itfclf infuch a manner as to form the external covering of the abdominal vifcera. TJie internal iiirface of the peritoneum is fmooth, its Chap. 17.] The Peril oneuM and Mefentery. 207 its external is rough, and united to the neighbouring mufcles and veflels by the intervention of cellular fub- flance. The cellular texture attached to the perito- neum, and in fome parts included within its duplira- tures, is generally replete with fat. The peritoneum is a denfe but thin and tranfparerit membrane, the ufes of which are to retain the vifcera of the abdomen in their places, and by the fmooth and moift covering* which it affords them, to prevent adhefions of one vif- cus to another ; for which it is excellently adapted by being continually moiftened by a ferous fluid, which proceeds from very minute pores. The exiftence of thefe is proved by fpreading a portion of the perito- neum on the end of the ringer, and then pulling it very tight on all fides ; by thefe means the pores are dilated, and fmall drops may be obferved to proceed from them. The mefentery is a production of the peritoneum, and is formed by two laminse of this membrane, in- cluding cellular fubftance. It rifes by a narrow origin from the firft, fecond, and third vertebras of the loins ; it advances forwards, and gradually becomes broader in its progrefs. The mefentery at length embraces the inteftines with its laminae, and thus affords them the coat which they derive from the peritoneum. That part of the mefentery which involves the fmall ihteftines is more properly called the mefentery j that which in- volves the large is diftinguifhed by the term mefoco- lon. The mefentery includes between its laminae all the blood -veflels and nerves which belong to the in- teftines, and allb the numerous lacteal veflels • which take up the chyle from the inteftines, and the glands with which thefe veflels are connected. The omentum or caul is alfo formed, by a dublica- ture of the peritoneum, including thin cellular fubftanc..', 9 vm& so8 , Omentum. [Book IJG -with a large quantity of fat. It is varioufly attached to feveralof the vifceraof the abdomen. The fuperior portion of it is divided into two borders, one of which is fixed to the arch of the colon, the other along the great curvature of the ftomach. Below this it is loofe, and is placed between the inteftines and the> anterior part of the peritoneum^ Befides this large membra- nous covering, called the great omentum, there is a much fmaller membrane of the fame kind, which is called the little omentum. It is fixed by its whole circum- ference partly to the fmall curvature of the flomach,- and partly to the concave fide of the liver. The little omentum is thinner and more tranfparent than the other, but its ftruclure is much the fame, and it is in fad a continuation of the larger* The omentum in man deicends as far as the navel, in quadrupeds much lower. The reafon for this dif- ference feems to be, that from the ereft pofture of man, the oily matter exuded from the omentum muft fall downwards to lubricate the inteftines, which are placed flill lower ; this, however, cannot happen in quadru- peds, which have the trunk of the body in a horizontal ficuation, and therefore fland in need of a longer om? n- rum ; but as the ufe of the omentum is not fully afcer- tained, this explanation is perhaps imaginary. Chap. 1 8.] [ 209 CHAP. 'XVIII. THfe STOMACH AND INTESTINES. General De/criptiox of the Stomach. — Length of the Inteftines in Man - and Quadrupeds. — Small and large Intcftinei. TH fe ftomach is a membranous fack, in form, when diftended, not unlike a bag-pipe. The ftomach js much larger towards the left fide than to- wards the right. It has two orifices, one towards its left fide, where the cefophagus or gullet enters, called the cardia, arid another towards the right, called the pylorus, which opens into the inteftines. The great extremity of the ftomach is in the left hypochondriurrii and for the moft part immediately under the diaphragm> yet the left orifice is not in the left hypochondrium, but almoft oppofite to, and very near the middle of the bodies of the loweft vertebra of the back. The fmall extremity of the ftomach does not reach to the right hypochondrium ; it bends obliquely backward towards the other orifice j fo that the pylorus lies about two fingers breadth from the body of the vertebrae, immediately under the fmall portion of the liver, and confequently lower down and more forward than the cardia. The ftomach is connected to the omentum, and by means of the omenturrij on the left fide, to the fpleen. Trie orifices of the ftomach are placed in the recefles on each fide of the fpine, and the body of the ftomach is clofely applied to -it, and in a manner bent round it. The orifices of the ftomach are therefore placed -further Jpack than its body, and are alfo a litfc higher, though VOL, III, P wheri tie The Stomach. [Book DC. when the ftomach is diftended its body rifes nearly to a level with its orifices. The body of the ftomach is d'ftinguifhed into two curvatures j the concave furface, which is applied round the fpine, is called the leffer curvature, and that which is convex, and is turned for- wards and downwards, the greater. The ftomach is formed of four coats. The external of theie is the peritoneal ; the fecond is mufcular, and is formed of fibres, which are continued from the muf- cular coat of the cefophagus. Thefe fibres are va- rioufly diftributed in the ftamach. Some run directly in the leffer curvature to the right orifice of the fto- mach, and are loft in the duodenum ; fome run down each fide of the ftomach, and are loft in its wideft part towards the left fide. Befides thefe longitudinal fibres, the ftomach is furrounded by fome which are circular, and which are alfo continued from the eefophagus. There is a large afiemblage of mufcular fibres round the right orifice of the ftomach, which conftringes it fo as to prevent the food from.pafling into the in- teftines before it has undergone the proper changes in the ftomach. Jf we examine the inner furface of the fmall extre- mity of the ftomach, where it ends in the inteftinal ca- nal, we obferve a circular border with a roundifh hole in the middle, which ft the pylorus, as before mentioned. The .border is formed, partly by a fold of the internal coats of the ftomach,, and partly by a collection of flefhy fibres fixed in the duplicature of the tunica cel- lulofa, and diftinguifhed from the other mufcular fibres by a thin whitifh circle, which appears even through the external coat, round the union of the ftomach and inteftines. The third cq^tof the ftomach, which conftitutes the gr.eate.ft part of its lubftance, is .the cellular, ora as it has. Chap. 1 8.] - x Int (films. ' 21 1 has been improperly called, nervous coat. This is thick, firm, of a white colour, and is connected to the mufcular by the intervention of cellular fubftancr, as it is alfo to the coat within. The fourth and inner coat of the ftomach is the vil- lous. This and the cellular coat, being more extenfive than the reft, are formed into numerous wrinkles or folds. It obtains the name ofvi/tous from the uneven- nefs of its furface, as being fimilar to wool or hair \vhen immerfed in water. It is fingle, of a red colour, and -is copioufly fupplied with mucus. The ftomach is furnifhed with lacleals, which rife moft numeroufly from it near its right orifice; jt is aH~p very copioufly furnifhed with nerves and b'ood- VelTels, which will be more fully defcribed hereafter. With refpedl to the ufes of the ftomach, they will be fpoken of at large in the chapter on digeftion. By the inteftines is meant the whole of the alimen- tary tube beyond the ftomach. They are divided into the finall and the large. The fmall inteftines are fub- divided into the duodenum, the jejunum, and the ileum. The large into the ccecum, the colon, and the rectum. All the inteftines, except fome part of the duodenum, are furrounded and fupported by the me- fentery. In man, the length of the inteftines is about fix times that of the body, but in graminivorous qua- drupeds their length, in proportion to that of the body, is much greater. 'I he fmall inteftines fill the middle and fore-parts of the abdomen while the large fill the upper and under .parts, as well as the fides of that cavity. The. fmall inteftines, in general, are of a cylindrical form. They are compofed of four coats, the ftruefture" of which is fimilar, and which bear the fame names as thofe of the ftomach. The mufcular coat, however, P 2 differs 21* Small lute/lines. [Book IX. differs from that of the ftomach in one refpect, that the longitudinal fibres are here lefs numerous, and the circular fibres much more fo. The fame fibre, how- ever, does not wholly furround the inteftine, as the circle is made of feveral imperfe<5t arches. The cellular coat is exactly the fame as that of the ftomach. It affords ftrength to the inteftines, and conducts nerves and blood-vefiels to and from the villous coat. The villous coat of the fmall inteftines is exceedingly exten- five, and forms, together with the cellular fubftance,, which connects it to the cellular coat, a vaft number of red femilunar folds or wrinkles, which ferve to increafe remarkably the internal furface of the inteftines, and of courfe to expofe the chyle more fully to the mouths of the lacteals. The fmall inteftines aflift in the preparation of the chyle, and propel their contents towards the great in- teftines. With refpect to the fmall inteftines in particular, feveral circumftances are to be noticed. The duode- num, fo named from its being about twelve inches irt length, differs from the others in not being entirely furrounded by the peritoneal coat ; its mufcular coat, however, is ftronger than that of the other fmall intef- tines, and its colour is more florid. The duodenum, beginning from the ftomach, firft runs towards the right fide downwards, and rather backwards; then it bends towards the right kidney, to which it is flightly con- nected, arid thence paffes before the renal artery and vein, afcending gradually from right to left, till it gets before the aorta and laft vertebra of the back. It con- tinues its courfe obliquely forwards by a gentle turn, and then terminates in the jejunum. Through this whole courfe the duodenum is firmly bound down and concealed by the folds of the peritoneum. The duode- num Chap. 1 8.] Inteftlws of Brutes. 213 num is more lax, and of larger diameter than the other fmall inteftines, and by i:s various rifmgs and fallings is calculated to retain the food for fome time before it pafles into the jejunum. About fix inches from the pylorus, the common bile duct and the duel: from the pancreas pour their contents together into the duode- num. Of the remaining part of the fmall inteftines, two fifths are called the jejunum, and the remaining three fifths the ileum, as no other characteriftic mark of dif- tindlion can be pointed out. The upper part of the fmall inteftines is indeed uniformly more red, rather wider, and its ftructure more robuft than the lower part, but the gradation is regular. Nothing particular is to be obferved at any part, which can furnifti a juft foundation for a change of name, and Haller accord- ingly comprehended the jejunum and ileum under the term of inteftinum tenue, or fmall interline. The je- junum is placed more about the umbilical region, the ileum more in the hypogaftric. The fmall inteftines at length terminate in the large, in the hollow of the right iliac bone, below the kidney. At this place there is a valve, which exhibits the appearance of a flit or chink. This valve permits a free paflfage from the fmall inteftines to the large, but prevents any thing from paffing readily from the large to the fmall. The caecum, which forms the beginning of the great inteftines, may be confidered as a production of the colon expanded into a bag. It is about four fingers in length and as many in breadth. It is fituated in the right iliac region, and refts on the broad part of the os ileum. At its lower part it has a long fmall procefs, called the vermiform, from its refemblance to an earth worm. This procefs is plentifully furnifhed with mucus, which it pours into the ceecum. In apes this P 3 procefs £T4 Large Lite/lines. [Book IX. procefs is wanting, but its place is fupplied by aglandj, which affords a flippery fluid. In fome birds we meet with two vermiform proceffes, and in fome kinds of fiih they are very numerous. Under the name of] colon is comprehended almoft the whole of the great intef- tines. The colon begins in the right iliac region, and is attached to the kidney, thence it rifes as high as the ftomach and the liver. It now runs tranfverfely before the fiomach to the left fide, is connected to the fpleen and kidney, defcends into the left iliac region, and being there bent in the form of the letter S, it termi- nates in the rectum. The ftructure of the colon is fimilar to that of the fmall inteftines. It is more robuft, however, and the longitudinal mufcular fibres, which are mixed with ligamentous fubftance, are united into three fafciculi, giving it in fome meafure a triangular form. Thefe fafciculi are continued from the vermi- form procefs of the caecum to the end of the colon, •where they gradually difappear. Along the whole courfe of the colon are a number of cells formed by circular contractions of the inteftine, which ferve to retard the progrefs of its contents. Along the whole courfe of the large inteftines we alfo obferve fmall projections of a fat fubftance, contained in elongations of their common coat. They feem in their nature very analogous to the omentum, and are confidered by Window as a kind of fmall omenta ; tfy-y are accordingly named appendices epiploicse. The rectum, which is a continuation of the colon, begins at the ioweft vertebra of the loins. It is bent like the internal fwrface of the os facrum and os coccy- gis, to which it is clofely applied, and terminates at the anus. The blood-vefiels of the inteftines wil be men- tioned in treating of the general diftribution of the ar- teries and veins. Chap. 19.] [ 21$ ] CHAP. XIX. THE LIVER, SPLEEN, AND PANCREAS. Nature and Situation of the Liver. — The Gall Bladder. — Bile Dufts.— Canfe of Jaundice. — The Spleen — The Pancreas.— Its Ufes. TH E liver is an organ of a deep red colour, and is by far the largeft gland in the body. It is fituated immediately beneath the diaphragm. .In man, the liver is divided into two portions or lobes, the larger of which is placed in the right hypochondrium, and the fmaller extends acfofs the epigaftric region, towards the left. The liver is divided on the upper and anterior fide into its lobes by a broad ligament, on the lower and pofterior, by a deep fiffure. The upper furface of the liver is convex and fmooth, correfponding to the concavity of the diaphragm. The lower furface is concave and uneven. The anterior and inferior margin of the liver is acute, the pofterior and fuperior obtufe. At the back part of the liver, near the great fiffure, there is a triangular eminence, called the fmall lobe of the liver, or lobulus Spigelii. The ligaments of the liver, by which it is fupported, are four. Of thefe, one fupports either lobe, and the broad ligament fupports the middle. Thefe ligaments are productions of the peritoneum, and are very different from what are called by the fame name in other parts of the body. They pafs from the diaphragm to the liver. Befides thefe, there is the round ligament, which is formed by the concretion of a considerable blood- veflel of the foetus, and pafles from the liver to the navel. Befides being fupported by thefe ligaments, P 4 the Si6 ?be Lher. [Boo the greatlobe of the liver is likewife connected by im- mediate adhefion, without the intervention of the perito- neum, to the tendinous part of the diaphragm. Round this adhefion we may obferve the peritoneum folded back, to form the external covering of the liver. The bjood-vefiels of the liver, which will be here- after particularly confidered, all enter on the concave fide of this organ, where it is divided into its two lobes. The ufes of the liver are to fecrete and prepare the bile. The gall-bladder is a membranous receptacle, fuffi- ciently large to contain two or three ounces of bile. It is connected to the inferior part of the right lobe of the liver in fuch a manner, that its fundus or bottom is placed forwards, and is in contact with the colon, and its neck is placed backwards. In fhape the gall-blad- der much refemble* a pear. It confifts of foqr coats, which are very fimilar to thofe of the inteftines, and are called by the fame names. The gall-bladder, as well as the liver, and the other vifcera of the abdomen are covered by the peritoneum. The duels, which ferve to, convey the bile formed in the liver to the duodenum, defer ve particular attention. The duel which comes from the liver, and is called the hepatic duct, is conftkuted of a number of frnaller duds, which rife through the whole fubftance of the liver. This duct is joined to another coming from the gall bladder, and thefe ducts together conibitute the common bile duct. The common duct defcends to- wards the pancreas, and patting behind the duodenum, pierces its external coat. After having run between the" coats of this inteftine for fome diftance, it is at length, between its fecond and third coat, united with the duct from the pancreas, and the fluids from the liver and pancreas Chap. 19. Cattfe of Jaundice. 217 pancreas being thus mixed, are poured together into the cavity of the duodenum. The gall-bladder in man receives all its contents by means of the communication between the cyftic an4 hepatic duels, In fqme animals, however, the gall- bladder receives hs bile by peculiar duels immediately from the liver, and in thefe animals the cyftic and he-, patic duels do not unite. From the ftruclure and con- nedYion of thefe ducts in man it is evident, that all the bile which pafies into the duodenum muft pafs through the hepatic and common bile duels, and that which goes to the gall-bladder pafles through the cyftic duel* The duds are furnifhed with a mufcular coat. The ufe of the gall-bladder feems to be to retain the bile till its more watery parts being removed, the remainder may become thicker, more pungent, and more acrid, It is fo placed that it may be preffed upon by the dif- tended ftomach, and its contents therefore difcharged when they are moft required to aflift in the procefs of digeftion, The gall-bladder is alfo emptied by the compreffion and agitation of the vifcera, which happen in vomiting. The bile in the gall-bladder fometimes concretes into hard maffes called gall-ftones. As long as thefe remain in the gall-bladder they occafion little or no inconvenience, but when they are propelled into the ducts they diftend and irritate them fo as, when of a large fize, to be productive of very violent pain. When thefe concretions are flopped in the common gall duel, they prevent the pafiage of bile into the in- teftines. The bile, not efcaping in the ufual manner, is accumulated in the liver, and being taken up by the abforbents is carried into the circulating fyftem, and produces jaundice. The fpleen is a fpongy vifcus, of a colour between deep red and blue. Its figure is fo irregular as to admit 2 1 8 Spleen, and Pancreas or Swtetlread. [Book IX. admit of no defcription ; it is fome what oblong, how- ever, but is convex on the fide which is applied to the ribs, and concave on that which is turned inwards to- ,!s the other vifce; a of the abdomen, and where it; - receives its biood-velTds. It is placed on the left fide, in the left hypochondrium, and is oppofite to the two kft ofthefalferibs. The fplcen is connected to the flomach by blood - veflels and a 'ligament, to the omentum, to the left kidney, to the pofterijr part of the diaphragm by the peritoneum, to the pancreas by veffels, and4 to the colon by a ligament. The fpleen has only one coat, which can be diflinclly perceived, and which is derived - from the peritoneum. The fpleen is extremely vafcu- lar, and when macerated feems wholly conftituted of numerous blood-vefTels. It has no excretory duel:, and it is remarkable, that though an organ of fuch confider- able fize, its ufe is entirely unknown. The pancreas is a glandular organ, of a pale red colour, and is called in certain animals the fweetbread. The pancreas is fituated in the epigaftric region, be- hind the flomach, in the triangular fpace furrounded by the windings of the duodenum. In form it referable? the tongue of a dog, the narrow termination of which is placed towards the fp'een, and is connected to that organ by blood-veffels. The pancreas in the human fubjecl: is eight or nine -inches in length but very nar- rowx and its fituation in the body is very nearly tranf- v./fe. The liquor prepared by this gland is remark- ably fimilar to that prepared by the glands which furnifli faliva to the mouth; fo that the pancreas may be confidered as the largeft falivary gland in the body. Lik^ the falivary glands, the pancreas is a conglomerate gland, or confifts^pf a number of fmall ghndular Chap. 19.] Pancreas or Sweetbread. 219 glandular mafies united by cellular fubflance. Near the pancreas is obferved a fmaller gland of the fame kind. This is called the little pancreas, and pours its contents into the pancreatic du6l. We have al- ready feen, that where the pancreatic du6l pours its contents into the duodenum, it is united with the com- mon bile duel. [ 220 ] [Book IX. CHAP. XX. THE ORGANS PLACED NEAR, BUT WITHOUT THE CAVITY OF THE ABDOMEN. The Glandule Suprarenaks.— The Kidneys. — The Bladder. r | ^ H E glandulae fuprarenales are two triangular JL bodies, the fabric of which is analous to that of glands. In the foetus they are larger than the kid- neys themfelves, over which they are placed; but in adults they are much fmaller. They are hollow, and are filled with areddifh matter. The right fuprarenal gland is fixed to the liver, the left to the fpleen and pancreas, both to the diaphragm, and each of them to the kidney, above which it is placed. They are furnifhed with no excretory duct, and their ufe is unknown. The kidneys are two organs of a pale red colour, and a firm confiftence, in farm refembling the beans which bear the fame name. They are placed with- out the cavity of the abdomen, on each fide of the fpine, and extend acrofs the two loweft falfe ribs as far as the bottom of the fecond lumbar vertebra ; they reft on the great plbas mufcle, the fquare muf- cle of the loins, and the tranfverfe of the abdomen, in fuch a manner that the right kidney is placed below the liver and the colon, fomewhat lower and further back, the left under the fpleen, the ftomach, the pan- creas, and the colon, fomewhat higher and more forwards. The length of the kidneys is about fix inches, their breadth about four. Of the two mar- gins of the kidneys, that which is placed outwards Chap, ao.] The Kidneys. ill. is convex, chat placed inwards concave. The kid- neys are varioufly connected to the vifcera, which are next them. The right kidney is connected to the colon, which, as mould have been before remarked, is here partly without the cavity of the abdomen. The kidney is made up of. three different fub- ftancesj firft, an external part of a pale colour, which chiefly confifts of numerous convolutions of blood- vefiels, and is called the cortical part. The other two fubftances, that is the medullary or ftriated, and the papillary, are really but one and the fame mafs, of a redder colour. The radiated ilriae are continued into the papillary portion, where they terminate ir> about eleven or twelve papillae, correfponding with the number of glandular portions, of which the kid- ney was originally compofed. At the point of each papilla we fee with the naked eye, in a flight depfef- fion, feveral fmall holes, through which the urine may be perceived to flow when the kidney is com- prefled. Each papilla lies in a kind of membranous calix or (heath, which opens into a common cavity, called the pelvis. The pelvis is alfo membranous, being a continuation of the calix. In man the cavity of the pelvis is not uniform, but diftinguifhed into three por- tions, each of which contains a certain number of calices, together with the papillae which they fur- round. The kidneys are furrounded with a ftrong firm membrane, which is very clofely applied about them. This, however, does not proceed from the peritoneum, but is connected to the pofterior part of that membrane by means of a large quantity of cel- lular fubftance, which is always plentifully filled with fat. The urine, which is fecreted in the kidney, drops from the papillas into the pelvis. All the fub-divi- i fions 222 fty Ureters^ [Book IX. lions of this bag ultimately terminate in a membra- nous canal, called the ureter, which, defcending be- tween the peritoneum and the great pfoas mufcle'j reaches the urinary bladder, to which it conveys the urine. The ureters of both kidneys enter the blad- der at the pofterior part, near the neck, which is th^» moft fixed point. They run fome diftance between the coats of the bladder, before they open into its cavity, and this ftrufture has the effect of a valve, in preventing the fluid when the bladder is very full, from returning towards the kidney. The ureters are about a fpan long, and their canal is much wider in fome parts than in others. They are in general about the fize of a writing pen, and are fomewhat curved in their courfe from the kid- ney to the bladder, fo as to refemble the letter^ They are furnifhed with feveral coats, one of which is mufcular. They are very fenfible, as is proved by the acute pain which perfons who are fubjecl: to the gravel experience while the Hones are palling through them. The urinary bladder is a membranous fack of con- fiderable fize. It is placed at the anterior part of the pelvis j when it is empty, it finks below the upper part of the oiTa pubis, but when filled, rifes confi- derably above them. It is larger in women than in men. The upper part of the bladder is called its fundus, which is much wider than where it terminates in its neck. The anterior part of the bladder, which is placed next the ofia pubis, is more flat, that turned backwards more convex. Its general form is a round oblong. The bladder in men is connected behind to the redtum, and before it is always attached by cellular fubftance to the ofTa pubis. It is alfo connected to the navel Chap. 20.] The Bladder. 223 navel by ligaments, which are the remains of two arteries of the foetus, and as its fundus pro] eels into the cavity of the abdomen, the bladder is alfo con- nected to the peritoneum, which covers part of its fundus. The coats of the bladder are, firft, a coat of cel- lular fubftance, by which it is connected to the neigh- bouring parts ; sdly, a mufcular coat, the fibres of which, beginning from the neck, afcend on both lides, towards the fundus. At the neck the fibres crofs each other, and in this manner form a fphinfter, by which animals are enabled to retain the urine; and yet a continuation of the fame fibres towards the fundus aflifts in expelling it. In this part, as well as in the tongue and mouth, we have an inftance of the dif- ferent parts of the fame mufcular fibres counteracting each other. " The third coat of the bladder is like the nervous coat of the interlines, and bears the fame name. The inner coat has many foldings, and is plentifully fup- plied with mucus. The fundus of the bladder alfo derives a coat from the peritoneum. The ufcs of the bladder are to receive the urine, to. retain it for a time, and to expel it through the urethra from the body. Had the peritoneum been fpread over the bladder in its whole extent, the weight of the vifcera in our erect pofture would have fo borne upon it, that a con- fiderable quantity of water could not have been col- lected there. ' The peritoneum, however, by puffing from the fides of the abdomen over the fuperior part of the bladder, forms a lupport for the incumbent vif- cera, and preferves a certain fpace below, where they cannot prefs. In the quadruped, where, from the ho- rizontal pofition of the body, the abdominal vifcera do not 224 Explanation of the Plates [BooklX* not prefs on the bladder, that organ is entirely inverted with the peritoneum. The figure in plate X. reprefents, 1. The trachea 2. The internal jugular vein* 3. The fubclavian vein. 4. The vena cava defcendens. 5. The right auricle of the heart* 6» The right ventricle, the pericardium being re* moved. 7. Part of the left ventricle. 8. The aorta afcendens. 9. The arteria pulmonalis* 10. The right lobe ol the lungs, part of which is cut off to fhew the great blood vefiels. 11. The left lobe of the lungs. 12. The diaphragm* 13. The liver. 14. The ligamentum rotundum. 15* The bottom of the gall-bladder projecting be- yond the anterior edge of the great lobe of the liven 1 6. The ftomach, prefied by the liver towards the left fide* 17. The fmall inteflines. 1 8. The fpleen. The figure in Plate XL reprefents* 1 . The under fide of the liver. 2. The ligamentum rotundum^ 3. The gall-bladder. 4. The pancreas, 5. The fpleen. S, The VOLJTT.. Chap. 20."[ Of the Vijcera. 225 6. The kidneys; 7. The aorta defcendens. 8. The vena cava afcendens. 9. The emulgent vein. 10. A probe under the fpermatic veflels and the arteria mefenterica inferior, and over the ureters. 11. The ureters. 12. The iliac veffels. 13. The inteftinum re<5lum . 14. The urinary bladder. VOL. IIJ. I 226 ] [Book IX. CHAP. XXI. THE CAVITIES OF THE MOUTH AND FAUCES, fcc. The Palate.— The Pharynx. ^-The Oefopbagus.—Tf.'e Larynx.— The Glottis,— T/Jt Epiglottis \— 7 'he ff'itisfyi/e. IT is unneceflary to enumerate the parts which ex- ternally limit the cavity of the mouth, as the lips, cheeks, &c. fince they are obvious to common obfer- vation. Within the mouth are the bony procefies which* include the teeth, and which are covered by the gums. The upper and arched part of the mouth is called the palate. The palate is divided into the hard and the foft. The hard palate is bounded by the teeth, and is formed by the two ofla maxillaria and offa palati covered with the periofteum and the common coat of the infide of the mouth, which produces, par- ticularly in fome animals, a number of hard ridges. The fofc palate or velum pendulum palatinum is a feptum, which arifes from the external margin of the palate bones, and laterally from a procefs of the fphe- noid bones. It is a moveable foft fubftance, hanging between the cavity of the mouth and the pofterior ter- mination of the noftrils. The ibfc palate is compofetl of the common mem- brane of the mouth and nofe, and includes a number of mucous glands, and fome mufcular fubftance. It forms two arches on, each fide, defcending from the hard pa- late. The two anterior of thefe arches are fmaller and thinner, and are inferted laterally into the tongue j the two pofterior are large, and are -connected behind to the pharynx. In the middle and upper part, where all Chap. 21.] 'The Palate, Uvula, fcfr. 227 all the half arches unite, they are lengthened' into a fmall pointed body, which is eafily feen at the back part of the mouth, and is called the columella or uvula. On each fide, in the bottom of the fpace which is left between the anterior and pofterior arches, is placed an oblong glandular body, which opens into the throat by eleven or, twelve excretory duels, and is called the amygdala or tonfil. We have the power of flopping the pafifage of air from the nofe, by drawing up the foft palate, fo as to cover its pofterior openings. The whole cavity of the mouth is moiftened by mucus, and the liquor from the falivary glands. The glands which furnifh the mouth with fpittle or faliva are the two parotids, which are feated immediately below the ears ; the maxillary, which are feated at th%e infide of the angles of the lower jaw ; the fublingual, which are placed between the bone of the lower jaw and the tongue; and laftly, a number of fmall glands, placed in bunches about the opening of the duels, which come from the parotid glands. The ftruclure of the* falivary glands is like that of the pancreas* I (hall defer the defcription of the tongue till I come to treat of the fenfe of tailing. The nofe, the ear, and the eye, will be defcribed when I treat of the fenfcs to which they are fubfervient. The cavity behind the palatum molle or foft palate is called the pharynx. At the back part it is bounded by the vertebras of the neck, above by the bafe of the cranium, before and laterally by the foft palate and much cellular -fubflance, and every way by the mufcles which furround the neck. The noftrils terminate at their pcflerior opening in the cavity of the pharynx, as do laterally the two euflachian tubes from the internal pare of the ear. The pharynx is a mufcular bag maped like a funnel, Qj2 beginning 21 8 Oefophagusy &f. [Book I. beginning from the bafe of the cranium and termi- nating below in the celbphagus or gullet. Its fubftance is merely mufcular, covered with the fame tender and glandular membrane which lines the mouth, fauces, and oefophagus. The ufe of the. pharynx is to receive the aliment and impel it into the cefophagus. The cefophagus or gullet is a membranous tube, be- ginning from the narrow termination of the pharynx. It is placed between the vertebrae of the neck and the windpipe, and defcending lower is embraced by the pleura, and lies in a triangular fpace behind the me^ diaftinum. Having arrived at the bottom of the tho- rax it pailes through the left perforation of the dia- phragm, and terminates in the cardia, or left orifice of the ftomach. The cefophagus has four coats. Firft, a covering from the pleura ; fecondly, a mufcular coat of con- fiderable power ; thirdly, a cellular coat ; and laftly, a tender internal coat, like that of the fauces, and which is copioufly fupplied with mucus, * he cefo- phagus conveys the food to the ftomach. The larynx is a hollow tube compofed of cartilages, mufcles, and ligaments, fituated behind and below the tongue, at the anterior part of the neck. The larynx is conne6led above to the os hyoides, behind to the root of the tongue and the pharynx. The cartilages of the larynx are the cricoid or an- nular, which is narrow before and broad behind, and is there divided mto two excavations, which receive the ^.rytenoid cr pyramidal cartilages. The cricoid carti- lage forms the bafis of the whole larynx. It is con- nected below to the windpipe, and above to the pyra- mid.il and thyroid cartilages. The thyroid cartilage relb perpendicularly on the cricoid, and conftitutes the upper, anterior, and largefl 6 part Chap. 21.] Larynx, &V. 229 part of the larynx. It confifts of two almoft quadran- gular plates of cartilage, which unite before, at an ob- tufe angle, but behind are feparate. This cartilage as harder and more prominent in men than in women, and has therefore been called the pomum Adami. At its pofterior part the thyroid cartilage has precedes above and below. The upper are united by means of ligaments with the procefTes of the os hyoides. The lower, which are Ihorter, are connected to the cricoid cartilage. The two arytenoid cartilages are the fmalleft, • which contribute to form the larynx. They are equal in fize, and when joined together referable the Ipout of an ewer. They are placed perpendicularly in two excavations of the cricoid cartilage at its pofterior part. The glottis is formed of two ligaments, in the follow- ing manner : Anteriorly the bafe of each arytenoid cartilage is fixed to one end of a ligamentary cord, which, by its other end, is inferted about the middle of the concave fide of the anterior portion of the thyroid. At the latter infertlon the two ligaments touch each other; but a fmall fpace is left between them, where they are connected with the arytenoid cartilages. This chink is what is called the rima glottidis, which is capable of contraftion and dilatation. Under thefe ligaments are two fmaller, which alfo arife from the arytenoid cartilages, and, running for- wards, are attached to the middle part of the thyroid cartilage. Between thefe fuperior and inferior liga- ments there is on each fide a fmall bag or cavity, called the vemriculus Galeni. Over the opening of the larynx, the rima glottidis, is placed a cartilaginous fubftance, called the epiglottis; it is fituated above the anterior or convex portion of the* cartilage thyroids, and its lower extremity is con- Qj netted 23 o Epiglottis, fcfr. [Book IX, netted by a fhort, broad, and very ftrong ligament, to the middle notch in the upper edge of that cartHage. The- epiglottis is fome what concave behind and convex before. Its fhape refembles that of the tongue, and its termination or apex is always free, fo as by its own elafticity to be naturally elevated. In deglutition, however, when the tongue is drawn backwards, the epiglottis is exa6tly applied over the rima glottidis, fo as to prevent the food from paffing into the larynx, or, as is commonly {aid, going the wrong way. The pharynx is every where connected by mufcular fibres' to the larynx, and the larynx is in a manner fuf- pendcd in its cavity. At the anterior part of the la- rynx is placed a gland of confiderable fize, called the thyroid gland. It is not difcovered to have any excre- tory duct, and its ufe is unknown. The mufcles which regulate the motions of the glot- tis, which is the principal organ of the voice, are the following four pairs, and one fingle mufcle : The crico-arytenoideus poflicus arifes from the cri- coid cartilage, and is inferted into the pofterior part of thebafe of the arytenoid cartilage, By its contraction it opens the rima glottidis a little, and by pulling back the p.rytenoid cartilage, renders the ligament tenfe. The crico-rarytenoideus latcralis proceeds from the cricoid cartilage laterally, \vhere it is covered by part of the thyroid, and is inferted into the bait of the aryte- noid cartilage. Its effect is to open the rima glottidis, by feparating the arytenoid cartilage.-, and confequently the ligaments which are fixed to them. The thyreo-arytenoideus arifes from the thyroid car- tilage, runs backwards along the fide of the glottis, and is inferted into the arytenoid cartilages. Its effect is tu bring the thyroid and arytenoid carriages nearer to each Chap. 21.] The Windpipe. 231 each other, and confequently to relax the ligaments which are placed between them. The arytenoideus obliquus arifes from the bafe of one arytenoid cartilage, and eroding its fellow, is in- ferted into the tip-of the other. When both act, they pull the arytenoid cartilages towards each other, and therefore contract the rima glottidis. The fingle mufcle which was mentioned is the ary* tenoideus tranfverfus. It arifes from the fide of one arytenoid cartilage and pafles to the other. It Hints the rima glottidis by bringing the arytenoid cartilages with the ligaments nearer each other. Befides thefe, there are a few feparate mufcular fibres, which from their connections are called The thyreo-epiglott'.deus, which arifes from the thy- roid cartilage, and is inferted into the epiglottis laterally. It draws the epiglottis obliquely downwards. The aryteno-epiglottideus, which arifes from the fide antj upper part of the arytenoid cartilage, and is inferted with the former into the epiglottis j it pulls down the epiglottis, and counteracts the effect of its elafticity. The afpera arteria, or windpipe, is a tube formed of annular cartilages, membranes, and mufcular fibres. It begins from the annular cartilage of the larynx, de- icends racher towards the right fide of the fpine into the cavity of the thorax, and is divided into two great branches, which being afterwards fubdivided, obtain the name of bronchia, and are diftributed through the fubftance of the lungs. The afpera arteria is furniflied with two membranes, the outer of which is formed of, cellular fubftance, and the inner is very fort and tender; between thefe membranes are placed the cartilaginous rings. Thefe rings are connected to each other by liga- mentous fibres above and below. They do nc con 232 The Wmdfye. [Book IX. complete circles, but are imperfect behind, where the circle is completed by a foft but ftrong glandular and mufcular membrane. The cartilaginous rings are thin and elaftic, but thicker and broader before than at their fides. They are largeft at the upper part of the wind- pipe, and are found to be fmaller as we advance lower. Of the mufcular fibres fituated between the cartilagi- nous rings, fome are circular, which render the wind- pipe narrower, and others longitudinal, which render it fhorter. The windpipe in the upper part of the cavity of the thorax is divided as was before ftated into two great branches, the larger and fhorter of which goes to the right lobe of the lungs, the fmaller and longer to the left. The ftru&ure of the branches of the windpipe, till they enter the fubftance of the lungs, is the fame as that of the windpipe j after they enter'the lungs, however, the cartilaginous rings foon difappear, and nothing but a thin elaftic coat remains. The ultimate divifions of the windpipe terminate in the air-vcffels of the lungs. Chap. 22.] • [ ' *33 3 CHAP. XXII. THE PLEURA, THE LUNGS, AND THE THYMUS. Defcription of the Tborax.-~-Tbe Pleura — The Brea/ls. — Breafts of Infants fontain Milk. — The Mediajlinum. — The Lungs, — The Thymus. TH E thorax is that part of the body which lies between the neck and the diaphragm. It is fur- rounded by the fpine, the ribs, the flernum, and the diaphragm, and alfo, internally, by a thin membrane like the peritoneum, which forms two feparate cavi- ties, and is called the pleura. On the external part of the thorax are placed the mammas or breads ; within is the heart, with its large verTels, and the lungs. The mammre, or breads, in men, and children of both fexes, are no more than cutaneous tubercles, with a brownifh circle in the middle, called the areola. In women they are two convex firm bodies, of a glandu- lar nature. In the middle of each bread is a promi- nent fpongy fubdance, called the papilla, perforated by a number of ducts for thedifcharge of the milk, around which is placed the areola. The internal part of the bread chiefly confids of a large quantity of fat; but there is alfo a large glandular fubdance, compofed of many .fmaller glands, connected together by cellular membrane ; this is the organ which fecretes the milk, a.nci to which the term mamma is more ftrictly appli- cable. It is remarkable, that a fmall quantity of milk may in general be preiled from the breads of new-born, infants, both male and female. The pleura, as has been intimated, is a tranfparent and dcnfe membrane^ continued through |he left per- foration 3.H fbt Pleura. [Book IX. foration of the diaphragm from the peritoneum. It covers the internal furface of the bones of the thorax and the upper part of the diaphragm, and involves the viicera of the thorax in the fame manner as below it involved thofe of the abdomen. The internal furface of the pleura is conftantly moiftened, and rendered flippery by a ferous' exudation. The mediaftinum is formed by two laminae of the pleura including cellular fubftance. Thefe are clofely connected near the fternum and vertebra? -, but in the middle and towards the lower part they are feparated by the pericardium and heart. Before the heart, from the pericardium to the fternum, the two laminse ad- here very clofely j higher up they are divided to re- ceive the thymus. The mediaftinum divides the thorax perpendicularly into two feparate cavities or faicks, which contain the lungs. The mediaftinum is attached in fuch a manner to the anterior part of the bones cf the thorax, as to render the right lack of the pleura larger than the kjft. Behind, the mediaftinum is attached to the dorfal vertebras, before to the fter- num,, below to the diaphragm and pericardium, and above to the large blood-veflels. Behind, tovvruds the vertebras of the back, is left a triangular fpace, in which is placed the windpipe, the cefophagus, the thoracic duft, and feveral large bloud- veflels j before, the gland called the thymus occupies a fimilar ipace. The ufes,of the pleura are to furnifh an internal covering to the banes of the thorax and the diaphragm, and an external covering to the tho- racic viicera. The iinian of the two facks of the pleura, forming the mediaftinum, is of ufe, by fupporting the lungs, and by preventing their prefiure on each other when the body is turned to either fide. By the two fides of the 'Chap. -2 2.] 'The Lungs. 235 the thorax being thus feparated, one may be wounded, without impeding the functions of the other. The lungs fill the two faoks of the pleura, one of which is placed on each fide of the mediaftimim. With refpect to the form of the lungs, their bafes are broad, and their fummits form an obtufe cone. Their ante- rior furfaces, and thofe applied to the mediaftmum, are flat, that next the ribs is fomewhat convex, and that behind round. The lower part of the left lung is excavated to make room for the heart. The colour of the lungs is in infants reddifh, in adults greyifh, and in old age they verge towards dark blue or black ; their furface is ufually mottled. The lungs are connected above to the neck by means of the windpipe, and below by blood- veflels to the .heart. They have no other covering but the pleura, connected to them by the intervention of thin cellular fubftance, which in this part is always free from fat. With refpect to the ftructure of the lungs, the right, which is larger, confifts of three lobes, the left only of two ; all of thefe are fubdivided into a number of fmaller lobes called lobules. Thefe divifions are con- nected to each other by the intervention of cellular fubftance. The fubftance of the lungs is ultimately made up of minute veficles, called the air-vefTels of the lungs, which are the terminal: ions of the wind- pipe. Thefe veficles have extremely thin coats, and on thefe coats are diftributed the minute ramifications of the blood-vefiels which go to the lungs. It has been computed, from the extreme minutenefs of the air- veffelsj that the internal furface of the lungs is not left extenlive than the floor of a moderate fized fitting room, Thefe air- veffels communicate with each other through 2j6 ¥be ffymas. [Book IX. through the whole fubftance of each lung, fo that by inflating one lobule the air paffes into the reft. The ufes of the lungs are of the moft important nature, and will be confidered in a feparate chapter on the fubjecl: of refpiration. The thymus, the fituation of which has been juft mentioned, is foft, andofafpongy texture. It is very large in the foetus, and is filled with a white thin li- quor ; in adults it is hard, fmall, and gradually decays. It is not difcovered to have any excretory duft, and its yfe is unknown. Chap. 23-1 [ 237 1 CHAP. XXIII. THE HEART. The Pericardium. — The Heart.— The Ventricles and Auricles. —Their TJ/l'j. — General View of the Blood- it, proceeds immediately under the Ikin, along the courfe of the ulna, to the internal condyle of the os humeri. It afterwards runs up along the infide of the arm, communicating freely both with the deep and fuperficial veins. The vena cephalica receives, at the extremity of the radius, branches which correfpond with thofe of the radial artery. The trunk runs along the radius, between the mufcles and integuments, com- municating with all the neighbouring veins j having pafled the fold of the arm, it afcends near the outer edge of the external portion of the biceps, ftill com- municating with the other veins, and pafilng between the large pecftoral and deltoid mufcles, terminates, as well as die bafilica, in the trunk of the axillary vein. Th* Chap. 2$.] Feins of the lower Extremities. itf The vena axillaris, which correfponds with the artery of the fame name, is formed by all the veins of the fuperior extremity. Above the axilla it receives branches from all the mufcles fituatec! about the fcapula, and the upper part of the thorax. Where it pafles be- tween the clavicle and firft rib, it changes its name from that of the axillary vein to that of the fubclavian. The fubclavian veins, receive the contents of the jugular and vertebral veins which come from the head, and alfo other branches from adjoining parts. The left fubclavian vein alfo receives a particular vein, called the imercoftalis fuperior, which proceeds from the upper intercoftal mufcles of that fide. The left fub- clavian vein alfo receives the contents of the thoracic duct, which is defcribed in^another place. The two fubclavian veins are directed towards each other, and uniting in the upper part of the thorax, ra- ther towards the right fide, conftitute the vena cava fuperior. Into the upper part of the vena cava opens a vein of confiderable fize, called the vena azygos, or the vein without a fellow. This arifes from the lower and internal part of the thorax, and foon pafles over to the right part of the fpine. As it afcends along the right fide of the thorax, it receives the inferior inter- coftal veins of that fide, and higher up a trunk com- mon to two or three veins, which alfo come from the intercoftals. At the top of the thorax it is bent for- wards over the right lung, and opens into the vena cava a little above the pericardium. The vena cava now perforates the pericardium, and defcends to the anterior or right auricle of the heart. The veins of the lower extremities, which terminate in the vena cava inferior, are The vena faphena major, which begins on/ the infide of the foot, at the great toe, and runs to the inner ankle; VOL. III. S here 258 Veins of the Leg and Thigh. [Book IX. here it receives other branches, and then runs up the- infide of the tibia, immediately under the fkin. After communicating freely, and receiving other branches, the faphena pafles along the in fide of the knee, and af- , terwards along the thigh as far as the middle of the fartorius mufcle ; it next runs on the fore part of the thigh to the groin, and at length opens into the top of the femoral vein. As this vein is quite fuperficial, it may be traced through the whole of its progrefs, when it is diftended with blood, by the naked eye. The vena faphena minor returns the blood from the outer fide of the foot; from this part it runs up on the outfide of the tendo Achillis, and next between the gaftrocnemius externus and the fkin. It terminates ia the vena poplitea a little above the ham. The vena tibialis anterior is a trunk which accom- panies the artery of the fame name, and terminates in the vena poplitea. The vena tibialis pofterior begins from the fole of the foot by feveral branches. Thefe, forming a trunk, run on the inner fide of the os calcis, and behind the inner ankle. It pafTes up between the foleus, and ti- bialis pofticus mufcles, accompanied by the corre- fponding artery, and opens into the vena poplitea. The vena peronea proceeds upwards along the infide of the fibula, almoft in the fame direction with the ar- teria peronea, and alfo ends in the vena poplitea. The vena poplitea, which correfponds with the artery of the fame name, is formed by the three large veins defcribed, but feems to be a continuation of the tibialis pofterior. The vena poplitea runs up immedi- ately on the mufcle of the fame name. About the ham it receives a number of branches from the joiat and from the neighbouring mufcles. A little above the ham it receives the name of the crural vein, which takes Chap. 25.] Vena Cava, &c. 259 takes its courfe upwards between the biceps and other flexors of the leg, clofely accompanied by the crural artery. When it has arrived oppofite the trochanter minor it receives three confiderable veins, the circum- flexa interna, externa, and profunda, which correfpond with the arteries of the fame names. About an inch below the ligament of Fallopius, it receives the vena faphena major, the courfe of which has already been defcribed. About this place it alfo receives the venae pudicac externse. After paffing under the ligament of Fallopius, and entering the pelvis, it changes its name to that of the external iliac vein. It now receives the vena epigaf- trica, which defcends towards it at the anterior part of the abdomen, and other venous branches from the adjacent parts. After having received the venous branches which correfpond with the arterial branches of the external iliac artery, the external iliac vein unites with the trunk of the internal iliac, or hypo- gaftric, vein, which returns the blood fent to the pelvis by the artery of the fame name. Thefe two venous trunks uniting, form the vena iliaca communis, and the iliacas communes of both fides uniting, form the inferior vena cava. This afcends on the vertebras but inclines towards the right fide, whereas the aorta is placed to- wards the left. It receives the venae lumbares, which enter it behind in pairs. Higher up it is joined by the emulgent veins from the kidneys, the vense capfu- lares from the glandulac fuprarenales, and by the right fpermatic vein. The left fpermatic vein commonly goes into rhe emulgent vein of the fame fide. Oppo- fite the liver the vena cava receives the blood from the diaphragm and pericardium. Hitherto, none of the veins which return the blood fent to the abdominal vif- cera by the cadiac and the two mefenteric arteries have S 2 been 260 reins of tie Vrfcera. [Book IX- been noticed. The courfe of this blood, however, de- ferves particular attention. The veins of the recbum form the beginning of a vein called vena meferaica minor, or vena hsemorrhoi- dalis interna. This afterwards unites with a branch from the left part of the arch of the colon, and opens at length into the vena fplenica. The vena fplenica returns the blood from the fpleen, and in its paflage alfo receives branches from the fto- mach, pancreas, and omentum, and alfo the vena meferaica minor laft defcribed. The vena meferaica major returns the blood of moft of the branches of the arteria mefenterica fupe- rior, which are diflributed on the fmall inteftines and right portion of the colon. It alfo receives the vena cscalis from the beginning of the colon, the gaftro colica, partly from the fromach and partly from the colon, and fome other branches from the adjoining vifcera> which vary in different fubjects. The vena fplenica receives the vena meieraica minor, and the vena meferaica major the vena fple- nica, and thus is brought into one vefiel, called the vena portse, the blood which comes from the omen- tum, the pancreas, the fpleen, the ftomach, and the fmall and great inteftines. The blood, however, thus collected, is not immediately returned to the heart, as in other parts of the body ; for the vena ports, having arrived at the concave part of the -liver, is firft divided into five branches, and tliefe into others more minute, which are diilributed through that organ like arteries, and which perform the fecretion of the bile. Where the vena portse enters the liver, its ftructure becomes more robuft, to enable it to perform its new office. The 'blood, thus circulated through the liver, is again collected by another fet of veins, which, uniting C h ap. 2 5 0 Explanation of the Plate of Vtins. a 6 1 uniting into two or three principal trunks, called vens hepaticae, pour their contents into the vena cava. The vena cava afcendens, having received thefe veins, per- forates the diaphragm and pericardium, and meeting with the fuperior cava, they empty themfelves together into the anterior auricle. The veins are reprefented in plate XIII. though not fo perfectly as I could have wiftied. aa. Vena cava. if. Defcending trunk of the cava. c.c. Afcending trunk of the cava, d.d. Subclavian veins. €. Vena azygos. /. Intercoftal veins. g. Mammary veins. i.i. Internal jugulars. /./. External jugulai s. m. Right axillary vein. n. Cephalic vein. 0. Bafilic. q. Phrenic. s.s. Emulgents. w.w. Iliac branches. x. Internal ilucs. 1. Vena facra. 2. Spermatic veins. 3. Epigaftric. 4. Saphena. ] i [Book IX. CHAP. XXVI. STRUCTURE AND COURSE OF THE LYMPHATICS. Two Kinds of Lymphatics.— Defcription of thefe Vefrcls. — Lymphatic Glands. — Latteals. — Thoracic Dv-8. — Receptacle oftbeCbjle, 13 c. LYMPHATICS are fmall pellucid veffels, which convey fluids perfectly, or very nearly, colourlefs. The lymphatics are of two kinds; thofe which take up fluids from the body in general, and thofe which receive the digefted aliment from the in- terlines. The latter kind are called lafteals, and both of them terminate in a common trunk, the thoracic dud. The lymphatics have at leaft two coats, which are thin and tranfparent, but tolerably ftrong. They have alfo nerves and mufcular fibres, as may be col- lected from their fenfibility when inflamed, and from their power of contraction. They are furnifhed with valves, which are placed in pairs, and which are fo numerous, that three or four of them often occur within the diftance of one inch. From this circum- flance they are frequently called valvular lymphatic vcflels, to diitinguifh them from the minute ramifica- tions of the fanguifercus fyftem, which alfo convey a colourlefs fluid. Lymphatics begin by extremely minute tubes from the whole furfcce of 'he body, from the cellular fub- ftance, horn fn ._k;> of the body, from all the glands, from all the viicera, and in general from every part of the fyftem. It Chap. 26.] Lymphatic Glands. 263 It is now well afcertained, that not only water is absorbed by the lymphatics on the furface of the body, but many other fubftances. No lymphatics have been demonftrated in the brain ; but from a variety of circumftances there can be very little doubt of their exiftence. All the lymphatics of the body pafs through cer- tain glands, which are connected with them. When the lymphatics approach thefe glands, they fend fome branches to neighbouring lymphatics j other branches pafs over the furface of the glands, and others enter their fubftance, in which they are fo minutely divided as to efcape obfervation. A great number of thefe glands are placed at the upper psrt of the thigh, be- longing to the lymphatics of the lower extremity; others are placed under the arm, belonging to thofe of the upper j and there are fimilar glands about the neck, and in various other parts of the body. It is at prefent difputed among anatomifts, whether lym- phatic glands are formed of cells or convoluted veffels ; but the latter opinion feerns to be more probable. Lymphatic or conglobate glands are of various fizes, from that of a fmall pea to that of a bean. They are commonly fome what flattened. In young fub- je6ls they are found of a reddifh or brown colour, but they become whiter in the progrefs of life. Their furface is fhining, which is owing to a fmooth denfe coat with which they are covered. Thefe glands are faid to be wanting in fome animals, which yet have lymphatic veflels. The lacteals are fo called from a- degree of white- nefs in their appearance like that of milk, which they receive from the colour of the fluid they convey. They arife from the villous coat both of the great and fmall inteftines, but principally from the fmall, S 4 particularly 2&i Lafteals. [Book IX. parricularly the jejunum j patting in their courfe through conglobate glands, they advance between the laminae of the mefentery towards the fecond or third lumbar vertebra, where they meet with the lympha- tics of the lower extremities. Of thefe Ibme are fuperficial, and others deeply feated. The former chiefly lie at -the infide of the leg and thigh, and follow the courfe of the vena faphena major. In the groin they pafs through lym- phatic glands. Being joined by the lymphatics of the lower part of the abdomen, they pafs under the liga- ment of Fallopius. The lymphatics of the lower extremities and pelvis, and the lacteals from the in- teftines, form the beginning of the thoracic duel:. This veflel alfo receives the lymph from the other abdominal vifcera. The thoracic duct, fo called from its courfe through the thorax, ufually begins about the fecond or third lumbar vertebra. It is of different fizes in different fubjects, and is fometimes extended at its lower part into a pyriform bag, called the receptaculum chyli ; but in general there is no enlargement fo remarkable as to de- ferve a particular name. The thoracic duct fometimes divides and again unites. At its beginning, it is fituated at the right fide of the aorta. It is afterwards obferved in the thorax, lying between the aorta and vena azygos. It "afcends as high as the fixth vertebra of the neck, where, forming an arch, it turns down- wards and enters the left fubclavian vein near the in- fertion of the internal jugular. The thoracic duct is furniflied with few valves, and thefe are placed without much regularity. At the place, however, where it is inferted into the fubcla- vian vein, there is a circular valve, which prevents the blood from getting into it. Bt fides Chap. 26.] Thoracic Duff. 265 Befides the thoracic duct, which receives the lymph from the lower extremities and the left fide, and the chyle from the inteftines, there is another veflel fomc- what fimilar, but much fhorter, on the right' fide. This receives the lymphatics from the right arm, the right lung, and the right fide of the head, and enters the right fubclavian vein at the fame place where the thoracic dud enters the left. [ 266 ] [Book IX. CHAP. XXVII. OF THE BRAIN, &c. fbe Dura Mater.— "The Falx.—Sinufes of the Brain.— The Pie Mater. — The Cerebrum and Cerebellum. — Source of the Optic Nerves.— The Pineal Gland. — The fuppofed Seat of the Sou/.— The Medulla Oblongata.— Source of the Nerves.— The Spinal Marronu. TH E cavity of the cranium is every way fur- rounded with ftrong bones, which have been already defcribed. Within thefe, before we arrive at the fubftance of the brain, we meet with two mem- branes, called by the antients the dura and pia mater, from an opinion that they were the fource of the other membranes of the body. The fame names are ftill applied to them by the moderns, though, as in many other cafes, the opinion which gave rife to them is exploded. The dura mater is a thick, firm, infenfible mem- brane, extremely full of blood veiTels. Its external furface performs the part of a periofteum to the in- ternal part of the fkull, to which it adheres by nume- rous blood veffels, particularly at the futures, where they pafs through the cranium to communicate with thofe of the external periofteum. Its internal fur- face is moiftened by the exhalation of a thin fluid, which prevents its adhefion to the membrane within. The dura mater forms feveral projections, which ferve very important purpofes. One of thefe, from its refemblance to the blade of a fcythe, is called th« falx. Its narroweft end is attached to the crifta galli 8 of Chap. 17.] T 2 c*i 2y 6 Brain of Birds. [Book IX. can be obferved here : which parts therefore cannot be confidered as neceflaryto the functions of life j we mighf, however, be led to imagine, that they are fub- iervicnt to the fuperior intellectual powers of the hu- man mind, did we not find that quadrupeds have thefc parts as well as men. Thefe appearances feem rather to depend on the various difpofition and direction of the fibres which compofe the brain j and the particular ufes which have been afiigned to the different parts of the brain feem to have no other foundation than the fancy of authors, who have indulged themfelves in fruitlefs fpec illations. Thofe birds which feek their food below the furface of water, mud, &c. have large nerves which run quire to the extremity of the bill, by which the fenfation of that part is rendered more acute. From the medulla oblongata, which is formed by the union of the cerebrum and cerebellum, arife not only the fpinal marrow, but almoft all the other nerves which perforate the bale of the cranium. The medulla fpinalis, or fpinal marrow, is a conti- nuation of the medulla oblongata, which paries through the great foramen of the cranium, and is continued «lown the bony canal formed by the vertebrse. The figure of the fpinal marrow is comprefied, being flatter behind than before, where we obferve a continuation of thofe grooves which divide the medulla oblongata into its lateral portions. In the medulla fpinalis thefe appear like two cords clofcly applied to each other, but which may be eafily feparated both before and be- hind till we come to their middle, where they are joined together by a thin layer of cineritious fubftance patting from one cord into the other. The fpinal marrow, like the parts of which it is a continuation, confifts of medullary and cineritious fubftance » the former, how- ever, Chap. 27.] Spinal Marrow. 277 ever, is here placed without ; the cineritious is placed within, and by a tranfverfe fection of the medulla fpinalis it appears to be in the form of a horfe-fhoe, the convex fide of which is turned forwards and its extremities backward. The fpinal marrow is inverted both with the dura and pia mater. The former of thefe in pafiing out of the foramen of the os occipitis, forms a kind of funnel, adhering at its upper part to the ligamentary fubftance which lines the bony canal of tjie vertebras. Lower down there is no adhefion, except where the nerves pals through the notches of the fpine, where the dura mater, which invefts the medulla fpinalis, fends out on each fide the fame number of meaths as there are gang- lions and nervous trunks. The pia mater is connected with the dura mater by means of a thin tranfparent fubftance, which from its indentations between the fpinal nerves has been named the ligamentum denticulatum. Its ufe is to fupport the medulla fpinalis, that it may not affect the medulla oblongata, or fpinal nerves by its weight, The lower end of the ligamentum denticulatum runs to the os coccygis far below the termination of the fpinal mar- row. Each lateral portion of the medulla fpinalis fends off, both from the fore and back parts, flat fafciculi of nervous fibres. The anterior and pofterior fafciculi are feparated from each other by the ligamentum den- ticulatum ; then pafiing outwards they proceed through the dura mater by two diftinct openings very near each other. Having penetrated the dura mater, the pof- terior bundle forms a ganglion, from the oppofite end of which the trunk comes out again, and is there joined by the anterior bundle. The membrana arachnoides is here very diftincl: T 3 from 27 & Spinal Marrow. [Book IX, from the internal lamina of the pia mater; fo that by blowing through a hole made in the arachnoides, it will fwell from one end to the other like a tranfparent inteftine. The fpinal marrow gives rife to about thirty pair of nerves. Thofe which come out between the vertebi^ of the neck are thinner than the reft, and are placed almoft tranfverfely j as we ciefcend, we find them run- ning more and more obliquely downwards, and when we arrive at the fecond vertebra of the loins, the fpinal marrow is fplit into numerous thread-like fibres, and from its appearance is called cauda equina, or the horfe's tail. The nerves which arile from the different parts of the brain and fpinal marrow will be treated of in a feparate chapter. Chap. 28.] [ 279 ] CHAP. XXYIII. STRUCTURE AND GENERAL DISTRIBUTION OF THE NERVES. Origin of the Nerves. — Extreme fubttlty of the Nervous Fibres.— Ganglions.— Plexus. — — Fontana1 s Microfcopical Obfervatiom on Nerves.-— Nerves from the Braia. — OlfaJlory and Optic Nerves, &c .— Auditory Nerves, &c. — Lingual Nerves, &c.— Sympathetic Nerve.-^Nerves from the Spinal Marrcnv.— Phrenic Nerve.--* Lkrfal and Brachial Nerves, &c. — Lumbar and Crural Nerves, £ff &c. Branches, by which the intercoftal nerve is conjoined with the fpinal nerves; viz. by the feventh and eighth of the cervical, and all the dorfal and lumbar, ry st The extremity of the intercoftal nerve, belong- ing to the firft nerve r, and the fecond s of the os facrum. /, A confidcrable nerve, arifing from the intercoftal near the vertebras of the back j here indeed it has fix beginnings, according to thofe branches by which the intercoftal is joined with the fourth, fifth, fixth, feventh, eighth, and ninth dorfal. Which nerve, here cut off, pafTes through the diaphragm into the abdomen, where it joins itfelf with the eighth pair of nerves of the brain, and with other branches of the intercoftal nerve, &c. u> A branch of the intercoftal nerve, U 3 w, w, &c. 294 Explanation of [Book IX. w} iv3 &c. Branches by which the right intercoftal nerve is joined with the fpinal nerves. x} yy Thofe branches of the right intercoftal, which ry s, reprefent of the left, z, z, Branches. A, A, Branches. B, B, The firft pair of cervical nerves. C, C, Branches, by which the fecond pair of cervical nerves is joined with the third. D, D, The fecond pair of cervical nerves. E, E, Branches, by which the third pair of cervical nerves is joined with the fourth. F, F, The third pair of cervical nerves. G, G, The fourth pair of cervical nerves. H I K, H I K L, The phrenic nerves, arifing by two origins, the one H from the fourth cervical fair, and the other I from the fifth. K, K, Their trunks, the left of which, upon account of the point of the heart's being turned to the left fide, is bended towards the left. L, The ex- tremity of the right, branched out upon the diaphragm. M, M, The fifth pair of cervical nerves. N, N, The fixth pair of cervical nerves. O, O, The feventh pair of cervical nerves. P, P, Branches of the firft pair of dorfal nerves, going to join the eighth pair of cervicals. Q^ R, &c. The coftal branches of the dorfal nerves, which run according to the length of the ribs. Qi Q, The firft, R, R, the fecond, S, S, the third, T, T, the fourth, U, U, the fifth, V, V> the fixth, W, W, the feventh, X, X, the eighth, Y, Y, the ninth, Z3 Z3 the temh, a, a, die eleventh, (3, |3, the twelfth. $1 A bianch of the fecond coftal nerve, which paries through Chap, a 8. J the Plate of Nerves. 295 through the external intercoftal mufcle, imme- diately under the origin of the ferratus magnus, which proceeds from the fecond rib ; afterwards it bends itfelf backwards according to the direc- tions of the origin of the ferratus magnus, and then diftributes itfelf upon the outfide of the latiffimus dorfi under the (kin. . . i, A fimilar branch of the third coital nerve, palling through in the fame manner, and diftributed as the former. £, A fimilar branch of the fourth coftal nerve, which when it has got under the fkin, winds partly back- wards, and partly forwards and downwards. /;, A fimilar branch of the fifth coftal nerve, which pafifes firft through the external intercoftal mufcle, then through the head of the external oblique, that part of it which rifes from the fifth rib, and after- wards runs along tinder the (kin. 6, », x, Branches of the feventh 0, the eighth i, and the ninth coftal nerve x, distributed to the in-* ternal part of the external oblique mufcle of the abdomen. A, A branch of the tenth coftal nerve, which,- after having paiTed through the external intercoilal mufcle and the tranfverfe, runs forwards between the tranfverfe and internal oblique mufcles towards, the recbus mufcle, and pafies through, it likewife by the aponeurofes of the oblique mufcles: to die parts below the fkin. /u, A branch of the eleventh coftal nerve, which fol- lows the fame courfe with that of the tenth, -A. vy A branch of the tenth coftal nerve, beftowed upon the infide of the internal oblique mufcle. £, A branch of the eleventh coftal nerve, beftowed the fame way as the laft, v. U4 296 Explanation of [Book IX. c, TT, Thefe appear to be branches of the twelfth coftal nerve, running between the tranfverfe and inter- nal oblique mufcles. £, This is a branch of the firft pair of lumbar nerves, running likevvife between the tranfverfe and inter- nal oblique mufcles. 0-, 35> Here the fecond trunks of the brachial nerves 28, 28, give branches to the pronatores and teretes, the radiales intern!, the fublimes, and palmares longi mufcles. 36, 36, Confiderable branches of the fecond brachial nerves, which fend off branches to the profundi, an4 the long flexors of the thumbs; and after- wards 37, 37, get in between thefe mufcles, and run down to the pronatores quadrati mufcles. 37, This fecond of the brachial nerves, paffes through the ligament of the wrift on the infide j after- wards, 39 proceeds to the wrift, where it di- vides itfelf into five branches, 40, 41, 42, 43, 44. Of which 40, The firft, gives a branch to the third lumbricati mufcle, after which it divides itfelf into two; one branch running along the fide of the ring finger next the middle finger, and the other along the fide of the middle finger next to the ring finger. 41, The fecond, gives a branch to the fecond lum- bricalj, and afterwards divides likewiie into two j one Explanation of [Book IX. one branch running along the fide of the middle finger, next the fore ringer, and the other along the fide of the fore finger next the middle finger. 42, The third, gives a branch to the firft lumbrical, and afterwards runs upon the fide of the fore finger next the thumb. 43, The fourth, goes to the thumb, and, there divid- ing into two, runs upon each fide of it. 44, The fifth, which is here cut off, gives a branch to the fhort. abductor of the thumb. And then it gets between the mort flexor and the mufcu- lus opponens of the thumb, and belongs to the opponens. 45> 45> Continuations of the brachial nerves. The third pair of brachials 29, 29, after having run backwards by the flioulder-bones from the axillse, and then between the external brachial mufcles on the one fide, and the long and fhort heads of the bicipites on the other, and after- wards between the internal brachials and long fupinators, emerge here 45, 45, between thefe Jail- mentioned mufcles, and thence proceed to the infide of the fore-arm, where having given off branches to the long fupinators and external radial mufcles, they pafs through the fhort fupi- nators 46, 46. 47, 47, Nerves cut off. 48, 48, Branches of the fourth brachial nerve, 30, going to die external brachial mufcle 49, 49, to the internal ulnar, 50, to the profimdus. 51, A branch of the fame, which pafTes under the internal ulnar to the back part of the extremity of the fore-arm, and makes a fubcutaneous nerve. After Chap. 28.] the Plate of Nerves. 301 After giving off this branch, the fourth brachial nerve runs before the ligament of the wrift in- wards, towards the palm of the hand, where it di- vides into the branches 52, 53, 54. Of which 52, The firft remarkable one, fpreading itfelf in the wrift under the tendons of the profundus and the iumbricales unufcles, its branches are diftributed principally to thefe, viz. the abductor of the little finger, the adductor of the fourth metacar- pal bone, the interofleous mufcles, the adductor of the thumb, the fhort flexor of the thumb, and the abductor of the fore finger. 53, The fecond, after it has given off the fubcura- neous branch which is here cut away, and an- other to the abductor of the little finger, runs along the back part of the little finger. 54, The third, dividing into two at the roots of the ring finger and little finger; one branch runs along the fide of the little finger next the ring finger, and the other along the fide of the ring finger next the little finger. [ 302 ] [Book IX, CHAP. XXIX. CIRCULATION OF THE BLOOD. Striiflure cf the Heart, and Circulation in cdd-blooded Animals.-^ Circulation in the euoarm-Llcoded Animals.— -dcurfe cf the Blood through the Lungs .-^-Through the reft of the Body. — Ramifications cf Arteries. — / alvular Structure of Feins.-*— Different from ihc Structure of Lymphatics. ' TH E ftructure and ufes of the organs concerned in the circulation of die blood have been al- ready coniidered, and it was farther remarked that the heart of man is of a duplex conftruction, in other words, that it has two auricles and two ventricles* With a view to perfpicuity, before we proceed to the circulation in the human body, it will be neceffary to mention the ftructure of the heart in certain animals in which it is more fimple. In frogs, ferpent^, and other cold-blooded animals> the heart confifts of only two cavities, an auricle and a ventricle j from the auricle the blood paiTes into the ventricle, from the ventricle it is driven into the arteries, from the arteries it is received into the veins^ and by the veins is again brought back to the auricle. This being well underftood, it cannot be difficult to comprehend the courie of the circulation in man, and the warm-blooded animals, in which the only difference is, that the heart being double, or con- fiding of four cavities, the blood performs two circles inftead of one. From the anterior auricle the blood paffes into the anterior ventricle ; froro the anterior ventricle "it is conducted by the pulmonary artery to the Chap. 2£.] Circulation through, the Lungs. 303 .the lungs, and from the lungs, the pulmonary veins bring it back to the pofterior auricle j from the pos- terior auricle it paries into the pofterior ventricle ; from the pofterior ventricle it is carried to every part of the body, by means of the aorta and its branches, and thence is again brought back by the venae cavas to the anterior auricle, whence it proceeded. In this manaer, throughout life, the blood is conftandy performing two circles ; a leffer between the heart, and the lungs, and a larger between the heart and the reit of the -body. The two auricles and ventricles are of equal capacity, and correfpond in their contractions. From thefe cir- cumftances it is evident, that the fame quantity of blood pafTes through the lungs in a given time, as through all the reft of the body, and, confequently, that the circulation muft be much more rapid in the lungs than in other parrs. It is fuppofed that about two ounces of blood are thrown from each ventricle of the heart at every contraction. The heart, however, though the moft remarkable, "is not the only organ of circulation ; fince every veflel through which the blood paffes aflifts, by its contrac- tile powers, to propel its contents. The fudden con- . tractions of the heart, by which the blood is thrown into the arteries, occafion their pulfation, which is moft violent in the large tjunks, gradually becomes lefs re- markable as they ramify and recede from the heart, and is not at all perceptible in the veins, which receive their blood from the arteries. The contraction of the ventricles, by which the blood is propelled from the heart, is called the fyftole ; the dilatation, by which the blood is received into them, the diaftpk, The ftrufture of the heart in the tortoife and fome other 304 Circulation in the Vcrtoifi, &V. [Book lX< other amphibious animals is intermediate between that of cold-blooded animals and warm-blooded. The heart has two diftinct auricles, without any com- munication : and under thefe, there is the appearance of two ventricles fimilar in lhape to thofe of the latter clafs : but they may be confidered as one cavity ; for the ventricle fends out not only the pulmonary artery, but likewife the aorta j for there is a paffage in the feptum, by which the ventricles communicate freely, and the blood pafies from the left into the right one. From the aorta the blood returns into the right auricle, while that from the pulmonary artery returns to the left auricle, from which it is fent to the left ventricle, &c. fo that only a part of the blood is fent to the lungs, the reft going immediately into the aorta ; hence the -animal is not under the necefiity of breathing fo often as otherwife it would be. The ends of the arteries are the beginnings of the veins, which uniting, as the arteries divided, at length form large trunks, which generally correfpond with the trunks of the arteries, from which, by the medium of fmaller branches, they received their contents. But though all arteries terminate in veins, yet the minutenefs of their ramifications, before this takes place, is various; while fome tranfnnit the red globulesr others exclude them, and tranfmit nothing but ferum. A circumftance contributing greatly to-the progrefs of the blood in the veins is their valvular ftru<5ture, fitting them for deriving affiftance from preflure j -and we find accordingly in the limbs, and wherever elfe' any advantage could be obtained from this circumftancey that the veins are furnifhed with valves, while in the cavities of the body, where they are not fo much, preffed by the action of mufcks, this part of their ftrudure is Wanting. The Chap. 29.] Circulation of the Blood. 305 The motion of the fluids of the valvular lymphatic fyftem is quite diflincl: from the circulation of the blood. Thefe veflels begin by open mouths, which perform the office of abforptioni and their contents are not de- rived, like thofe of the red veins, from the extremities of arteries ; their fluids are therefore propelled, with- out any aid from the heart, by their own contractile powers. The moft remarkable functions, to which the circu- lation of the blood is fubfervient, are fecretion, the nourifhment of the body, and certain changes which the blood undergoes in its pafifage through the lungs j 6f thefe it will be proper to treat in the chapters im- mediately fucceeding. - VQL. III. CHAP. XXX. SECRETION, EXCRETION, ABSORPTION, AND NOURISHMENT. General Jffitfs of Secretion. — The Gland f. — Excretion. — Secretion ef Bile.'*~Ho to one fet of hens a piece of old mortar was given, which they broke down and fwal- lowed, certainly not miftaking it for Canary feed, or any kind of food, but diftinguiihing it from a piece of brick, which they did not either break down or ("wal- low -, another fet at the fame time were kept without; any calcareous earth ; many of thefe died, while the others, although otherwife exactly in the fame circum- flances, were none of them loft. It appears therefore that birds have a neceffity for (tones being fwallowed for digeftion, and earths for ether purpofes, and that they have an inftinft which dilpofes them to choofe the proper quantity and quality required. Moreover, as Mr. Hunter obferves, the noife of the grinding may be heard, and therefore there can be no doubt that this ftomach is made to contain Hones for the fame pur* pofes for which teeth are employed *.' The lobfter is furnilhed, for the comminution of its food, with an apparatus which is fituated at the pylorus. It confifts of two bony furfaces, formed into ridges, which are applied to each other like thofe of the molares. They are alfo' covered, like our teeth, with enamel, and furnifhed with mufcles, by which the action of -grinding is performed. In order to difcover the power of the gizzard, Reaumur gave to a turkey fmall tubes of glafs, five lines in length and four in diameter; thefe were broken in' the gizzard in twenty-four hours. In the place of glafs tubes he fubftituted tubes, of tinned * Fordyce on Digeftion, p. 24, &c. iron, 3i S Reaumur's Experiments. [Book !}£. iron, fevcn lines in length and two in diameter, clofec! v/ich folder at each end. Some of thefe were indented by the action of the gizzard, and others crufhed quite flat. Similar tubes, placed between the teeth of a vice, required a force of four hundred and thirty-fix pounds ?.nd a half to produce the fame effects. Inclcfing in tin tubes, properly perforated, fomc grains of barley, fome unboiled, fome boiled, and ethers peeled, and letting them remain- a day or two in the iiomach, he found them only a little fwelled. The fame experiment being tried with rneal, the fame confequences were obferved, as it did not 'become in the fmalleft degree putrid. From thefe experiments Reaumur concluded, that digeftion, in birds provided with a gizzard, was chiefly performed by means of trituration. Such are the powers of the gizzard ; but thofe of the membranous flomach, though of a very different nature, are not lefs aftonifhing. It is well known that birds of prey, which fwallow every part of the animal they devour without much diftinction, have the power of throwing up luch parts of their food as they can- not digeir. Taking advantage of this circumftance, the fame naturalift, gave tubes, fimilar to thofe above mentioned, and rilled with flem, to a buzzard hawk ; in twenty- four hours the tubes being thrown up, the meat which they contained was reduced to an oily pulp, and with no appearance of putridity. At the end of forty-eight hours, the decompofition was ftill more perfect, the pulp was more attenuated and blanched, and that conftantly without any fmell. The tubes being filled with the bones of young pigeons, inftead of butcher's meat, thefe were converted into a jelly in twenty-four hours. Beef bones, very hard, and deprived both of flefh and marrow, out of forty Chap. 3 1 .} Balls of Hair m Stomachs cf Animals. 3 1 9 grains loft eight in twenty-four hours, and in three days were totally diffolved. Grain and fruit expoicd to the fame procefs, were very little if" at all affected. Digeftion, therefore, in birds of prey is performed by a fluid, which acts only upon animal matter. This - fluid is very abundant in the ftomachs of thefe ani- mals. Small pieces of fponge, of thirteen grains, {hut up in the tubes, weighed three grains more when thrown up. Notwithftanding thefe effects of the digeftive or- gans, the motions of the flomach and the gizzard arc fcarcely perceptible. There is reafon, however, to believe, that the little motion they have is very re- gular. On examining the furfabe of the balls of hair which are found in the ftomachs of animals which lick their coats, the hairs in each hemifphere feem to arife from a center, and to have the fame direction, which is circular, and correiponding with what would appear to be the axis of motion. This regularity in the direction of the hair could not be produced if there was not a regularity in the motion of the ftomach. The fame is proved in fome birds, as the cuckow, which fometimes feeds on hairy caterpillars. The principal inftrnment of digeftioh in rrtoft ani- mals, is however now generally fuppofed to be the gaftric juice ; a fluid which diftils from certain glands, fittiated in the coats of the ftomach, nnd mixes with the food as foon as it is received into that organ. The Abbe Spalanzani, in order to obtain a fight of the gaftric juice, introduced tubes, containing bits of fponge into the ftomach of a crow. In four hours the tubes were vomited up, and the fponges, being prefled, yielded thirty-feven grains of gaftric liquor, which was frothy, of a turbid yellow colour, had a tafte intermediate between bitter and fait, and being 320 'Gaftric Fluid. [Book IX,- jfet to ftand in a watch glafs, depofited in a few hours a copious fediment. As the fediment might be attri- buted to the food fufpended in the gaftric juice, the experiment was repeated on a crow, the ftomach of which was empty. The fluid obtained in this cafe was of a tranfparent yellow colour, depofited very little fediment, but the tafte was the fame. The gaftric juice did not burn when thrown on hot eoals, and paper moiftened with it would not burn till the fluid was evaporated. The motion of the ftomacK alfo aflifts in mixing and intimately blending this fluid with the proper parts of the aliment, fo as to enable its foiven: powers more completely to act upon it. The fenfible qualities of this fluid are, however, not fuch as to lead us to at- tribute to it any fuch power j and I do not know that it has been completely analized by any chemical procefs, at leaft by any which enables us to explain its folvent property. A French * author, indeed, ob- fcrving the power which inflammable air has in dif- folving the texture of animal matter, has intimated an opinion, that a portion of the oily matter which is taken in with the food, may be modified by the ftomach into inflammable air, and may perform this part of the procefs of digeftion. Digeftion differs from all other procefles, and can be compared neither to putrefaction nor chemical folution. A remarkable circumftance alfo with regard to digeftion is, that by it both animal and vegetable matter is converted into the fame fubftance.. Dr. Fordyce fed a dog with farinaceous matter, and another with mufcle, and opening them both (in which he does not appear to have been juftifiable) * M. Sage* during Chap. 31 «] Digeftion 'of Fijhes. 321 during the time that the chyle was flowing through the lacteals, he collected from each as much chyle as he was able. On examination they were found fo fimilar, that the difference could not be diftinguifhed by any experiment which he could contrive. The chyle of a cat living on fielh, according to the fame gentleman, cannot be diftinguifhed from that of an ox or flieep. Live or frelh vegetables, when taken into the fto- mach, are firft killed, by which a flabbinefs of tex- ture is produced, as if they had been boiled, and then they begin to be acted on by the gaftric juice. This fluid, indeed, Teems to have no power to act on living matter, fince worms remain uninjured in the ftomach. Digeftion, however, as far as relates to the diffolution of aliment, may be carried on out of the body by means of the gaftric juice, and the applica- tion of heat equal to that of the human body. This procefs is continued for fome time after death, and the ftomach, no longer protected by the living principle, is itfelf partially diflblved by the gaftric juice. In the ftomachs of large fifh are commonly found fmall fillies, ftill retaining their natural form » but when touched, they melt down into a jelly. From thrs circumftance, and from the great quantity of fluids poured into their ftomachs, we may conclude, that digeftion is folely effected in them by the dif- folving power of a menftruum, without the aid of trituradon. Neither animal nor vegetable fubftances can undergo their fpontaneous changes, while digeftion is going on in them. The gaftric juice even has a power of recovering meat already putrid ; for let putrid meat be given to a dog, and the contents of his ftomach will be found fweet, and free from all putrefaction, VOL. III. Y if -322 Power of Coagulation in tie Stomach. [Book IX. if he is killed a fhort time after. Bread, which has remained in the ftomach of a dog for eight hours, is fo much changed, that it will not run into the vinous fermentation, but when taken out and kept in a warm plate becomes putrid. Its putrefaction, how- ever, is not fo quick as that of a folution of meat which has been in the ftomach for fome time. The effects are fimilar when milk and bread are the food. When the digeflive power, however, is not perfect, then the vinous and acetous fermentation will take place in vegetable matters, and the putrefactive in the ftomachs of animals which live wholly on flelh. The gaftric juice apparently preferves vegetables from running into fermentation, and animal fubftances from putrefaction, not from an antifeptic quality in that fluid, but from a power of making them go through another procefs. In moft ftomachs there is an acid, even though the animal has lived entirely upon meat for many weeks ; this, however, is not always the cafe. The acid fometimes prevails fo much as to become a difeafe. The ftomachs of many animals have a power of • coagulating milk ; this is continually feen by infants throwing up their milk in a coagulated ftate, and the .fame thing may be obferved by feeding a dog with milk, and killing him half an hour afterwards. The ftomach of the calf, and perhaps that of other animals, . preserves this power after death, and is kept dried, far the purpofe of making cheefe. Indeed milk, raw egg, and feveral other fubftances, .require to be coagu- lated, before they can bedigefted. If we throw milk into a portion of the jejunum* that milk will be abforbed by the lacteals ; but if we throw milk into the ftomach of the Tame animal, the milk will not be abforbed by the lymphatics ; there- fore Chap. 3 i.] Proofs ofDigefiion. 323 fore an argument might be brought* that the abfor- bents of the ftomach would refufe what the abforbents of the jejunum would readily take up. But it muft be confidered thar the milk is inftantly coagulated in the flomach, and not in the jejunum, which coagula- tion will perfectly prevent it from being abforbed 3 but all thofe fubftances which are not changed by the coagulating juice of the ftomach will be, and are equally taken up by the lymphatics in the ftomach and lafteals. There is, therefore, a converfion of the food in the ftomachr into a new fubftance, whofe pro- perties are at prefent unknown, which new fubftance is the only one which can be converted into chyle in the duodenum and jejunum, exactly as we may form fari- naceous matter, mucilage, and native vegetable acid into wine j but before they can poffibly be converted into wine, they muft,firft be formed into fugar* So in a fimilar manner farinaceous matter, gum, and white of egg, are all capable of forming chyle ; but before they are formed into chyle, they muft be converted into a matter certainly not fugar, but a matter of a particular fpecies in the ftomach, and by the ope- ration of the ftomach, this particular fpccies of matter is afterwards converted into chyle in the duodenum and jejunum. Dr. Young, of Edinburgh, found that an infufionof the inner coat of the ftomach, which had been pre- vioufly warned with water, and then with dilute folu- tion of mild fixed vegetable alkali, fo that it was not pofiible that any acid could have remained in it, coa- gulated milk very readily. He found alfo that it had the power of coagulating ferum, and other animal mu- cilages. The coagulating power of this fubftance is very great. Dr, Fordyce mentions that fix or feven Y 2 grains 324 Caufe of Flatulency. [Book IX. grains of the inner coat of the ftomach infufed in wa- ter, gave a liquor which coagulated more than a hundred ounces of milk. - All fermentation is quite foreign to perfect di- geftion, and when it does take place, is always propor- tioned to the diforder of the ftomach, fmce very little if any wind or flatulency is generated in the ftomachs of thofe, whofe digeftion Is moft quick and eafy. It is not uncommon, however, for milk, vegetables, wine, 'and whatever has fugar in its compofition, to become fooner four in fomc ftomachs than if left to undergo a fpontaneous change out of the body ; and even fpirits^ in certain ftomachs, almoft immediately degenerate into a very ftrong acid. All oily fubftances, particularly butter, become rancid very foon after being taken into the ftomach, and this rancidity is the firft procefs in the fermentation of oil. Animal food does not fo readily ferment in difeafed ftomachs, when com- bined with vegetables, as when it is not, Flefh meat appears to undergo no change preparatory to digeftion, but feems at once to fubmit to the action of the gaftric juice. It appears firft to lofe its texture, then becomes of a cineritious colour, next gelatinous, and laftly, is converted into chyle. In order to afcertain whether the production of any degree of acidity is efiential to digeftion, Dr. For- dyce made feveral experiments, from which he con- cludes, that in perfect digeftion no acidity whatever is produced. If the gaftric juice is applied to a fubftance out of the body, in a proper temperature, it will produce changes in it, fimilar to thofe which take place in the commencement of digeftion ; but by applying gaftric juice, the watery fluids of the ftomach, the faliva, the bile, Chap. 31.] Digeftible and indigeftible Matters. 325 bile, the pancreatic juice, altogether or feparately, in no cafe has chyle, or any thing like it, been formed. It is not yet afcertained what are the circumftance-s -•vhich contribute to render different articles ufed as food, digeftible or indigeftible. Something is un- doubtedly to be afcribed to firmnefs of texture, fince cuticle, horn, hair and feathers, which are indigeftible in their natural ftate, became digeftible and nutritious when reduced to a gelatinous form by Papin's digefter. That the folubility or infolubility of a fwbftance in the ftomach is not, however, merely owing to the degree of folidity, is proved from a circumftance already mentioned, viz. that boiled barley was not acted on by the gaftric juice 'of a buzzard hawk, while pieces of hard beef bone, expofed to its action in the fame man- ner, were completely difiblved. But fubftances may even be rendered too foft $ for a fluid is difficult of digeftion, and its continued ufe very injurious to the ftomach. It may be remarked, that nature has given us very few fluids as articles of food. It therefore feems, that fubftances may be either too compact or too lax in their ftructure, to render them fit fuctjects to be acted on by the dige.ftive powers. The degree of cafe, however, with which fubftances are digefted, feems in many cafes owing to a differ- ence in folidity. Brain, liver, mufcle, and tendon are digeftible in the order in which they are here in- ferted. Boiled, roafted, and even putrid meat is eafier of digeftion than raw. Hufks of feeds and the hulls of fruits are indigeftible in their natural ftate, but to what circumftance this is owing is not fully afcer- tained. The whole of our food is fometimes not di- gefted ; this may arife from two caufes, either from fome parts of the food being of too firm a texture to Y 3 be 326 JXgcftible and indigeflible Matters. [Book IX. be diffolved fo foon as the other parts are converted into chyle and carried into the duodenum : or from the ftomach being fo much difordered as to digeft im- perfectly. This diforder of the ftomach fometimes proceeds fo far, that the food pafTes through the body almoft unchanged. ' Jn fome cafes food has been re- tained on the ftomach for twenty^four hours, and thrown up without being altered in the leaft. The effential oils of animals and vegetables are indigeftible ? they are foluble, however, either in the gaftric juice or the chyle, by which means they be- come medicinal from their ftimulant powers. The eflential oils of vegetables, but more particularly thofe of animals, feem to pervade the very fubftance of the animals whofe food contains much of them. Thus fea birds, which feed on fifh, tafte very ftrongly of them, and thofe which live on that food only during certain times of the year, as the wild duck, -have that tafte only at certain feafons. Two ducks were fed, one with barley, the ether with fprats for about a month, and killed both at the fame time ; when drefled, that fed on fprats was hardly eatable. Animals eat lefs in proportion as their food is more nutritious. Thus carnivorous animals require much lefs food than the granivorous, and thefe, than the graminivorous ; animals, indeed, of the laft kind, em- ploy almoft the whole of their time in eating. A correfponding relation is alfo obferved with refpect to the digeftive organs in thefe feveral races of animals ; Carnivorous animals have only one ftomach, grani- vorous animals very generally two, and graminivorous animals four ftomachs, with a greater length of in- teftines. From which circumftances it may be col- lected Chap. 3 1.] Digeftion ofjleeping Animals, &c. 327 k(5led, that grafs is more difficultly afllmilated than grain, and grain than flefh. The firft flomach in ruminant animals, fuch as the bul3, the fheep, &c. is a receptacle which has a very weak aclion on the food, and from it the ani- mal has the power of returning the food into the mouth, to undergo a fccond maftication. In Mr. Hunter's paper on Digeftion, .publilhed by the Royal Society, there is the following curious obfervation, which iliuftrates very much the ufe of thefe previous ftomachs : milk fucked in by the calf does not remain in any of the previous ftomachs, but paries down in- ftantly into the digefting ftpmach, not requiring any previous operation j but grafs remains for a length of time in the previous ftomachs. I fit is allowable to extend our views beyond the animal kingdom, we might fancy that the digeftive procefs in vegetables is ftill more difficult than it is in the graminivorous animals, fince vegetables are continually taking in nourifhment, and confume an immenfe quantity of air and water in proportion to their growth and bulk. When vegerables, howe- ver, are furniihed with matter which has undergone more preparation than mere air and water, viz. pu- trified vegetable matter, their growth is far more rapid ; and they flouriih ftill more on the remains of the ani- mal kingdom. Sleeping animals do not digeft during winter. Worms and pieces of meat were conveyed down the throats of lizards, which were going into winter quarters, and which were afterwards kept in a cool place. On opening the animals at different periods/ the fubftances were found entire and without altera- tion. Some of the lizards voided them in the fpring >vith little or no alteration produced in them. Di- Y 4 geftion 32$ Digeftmg ofjkeping Animals, fcfr. Book IX. geftion is therefore regulated by the ftate of the other functions of the body *. By hunger and cuftom animals may be taught to eat, and even to prefer, a very different kind of food from that naturally defigned for their nourifhment : thus pigeons have been made to live entirely on flefh. Whether the gaftric juice is altered in its nature by a difference of food, or in what other way the fyftem accommodates itfelf to fuch a change, it is not eafy to determine. * Hunter on Digeftion. — See his volume on the Animal Economy. Chap. 32.] [ 329 ] CHAP. XXXII. RESPIRATION' AND ANIMAL HEAT. Refpiration in part an ir.^johinta;-; F*»8ion — Fc:;r Sts-res r.f Refpira- tion.— U/es of Refpiration. — Rffpiraiion of Iiif tis different from that cf other Animals.— Tkt red 'Colour of the Blood derived from the Air in Refpiratic/i. — Dr. Prig/Heft Experiments. ~— Dr. Goodnvyn's Experiments. — The oxygenous Part of the Air dimi>..jl:-i.d by Refpi- ration.— Fixed Air generated in thz Lungs in Refpiration and expired, — Animal Heat produced by Refpiration. — Inftanced in different Animals. — Dr. CfOfwfortTs ingenious Theory. T TNINTERRUPTED refpiration being neceflkry \^J to our exiftence, it is wifely ordained, that this function Ihould be fo far involuntary as not to require a continual and irkfome attention. For other pur- pofes, as that of fpeech, refpiration is no lefs wifely fubmitted in fome meafure to our direction, fo that within certain limits we can accelerate or retard it .an pleafure. We are fufficiently prevented, however, ; from fulpending. refpiration to fuch an extent as to in- terfere with other procefies abfJlutely neceffary tu the fupport of life, by being fubjected, whenever we ce^fe to breathe, to a fenfation inexpreflibly diftreffing, and which compels us to ufe every effort in our power to inhale air into the lungs. The thorax, or that bony cafe which furrounds and protects the lungs, is furniflied with a number of mufcles, fome of which, by drawing. the ribs upwards, enlarge its capacity, and others, by drawing them downwards, diminifh it. Its capacity, however, is ftill more influenced by the mufcular organ called the dia- phragm, which from the breaft bone and lower ribs pa fifes 33 3 Four Periods in Refpiration. [Book IX. pafles obliquely downwards to the loins, and feparates the thoracic from the abdonainal vifcera. By the contraction of the diaphragm, the abdominal vifcera are prefled downwards and forwards, by which the lungs are permitted to expand themfelves in the fame direction j when the diaphragm is relaxed, and the abdominal mufcles are thrown into action, a directly oppofite motion takes p]?£e ; the vifcera of the abdo- men are prefied upwards and backwards againft the lungs, from which part of the air is confequently ex- pelled. The air, which is to be con fide red as poflefllng many properties in common with other fluids, poffefFes this, that by its weight it enters where it is lead re- filled. Part of the refiftance to the entrance of the air into the lungs being taken off by the action of the mufcles dilating the thorax, it rufhes in through the windpipe, in the fame manner as it rufhes into the cavity of bellows, when the boards are feparated from each other. Infpiration and expiration therefore are not performed by the lungs themfelves, fince air would be equally drawn into and expelled from the cavity of the thorax when deprived of lungs, fup- pofing that the parts of the thorax could be made to perform their motions perfectly well after death. The lungs may therefore be compared to the cavity of bel- lows filled with any downy fubftance, the bones of the thorax to the boards of the bellows, and the mufcles of the thorax to the hands by which the bellows are moved. Refpiration may be divided into four ftages or pe- riods j rirft, infpiration ; fecondly, a paufe when the lungs are filled j thirdly, expiration ; and laftly, a paufe when the lungs are emptied. We are equally ftimu- lated to infpiration and expiration by a fenfadon of uneafmefsA Chap. 32.] UJes of Refyiraticn. 331 uneafinefs, but that which is felt when the lungs arc kept too long inflated after a full infpiration, is of a different kind from that which is perceived when they are preferved too long empty after expiration. In the former cafe the uneafinefs is referred to the head, in the. latter to the cheft. To what thefe fenfanons arc owing we canno: altogether determine ; they are pro- bably, however, to be attributed to the anterior cavi- ties of the heart and the veffels of the head being overloaded with bloodf which cannot fo readily pafs through the lungs while their motion is fufpended. The truth of this opinion is much confirmed by the fluffing of the face, and the burfting of blood veflels, which fometimes happens from impeded refpiration. The air, after paffing through the windpipe, is con- veyed by its ramifications to. the air veffels of the lungs. After infpiration the air veffels, which are to be con- fidered as very minute bladders with thin coats, arc fully diftended. The minute and very numerous ra- mifications of the pulmonary artery are diftributed on the membranes of thefe air vcffds -, and through the ' membranes, without coming into direct contact wich the blood, the air produces thofe changes on it, which are found to be abfolutely neceffary for the continu- ance of life. The chief ufes of refpiration, as far as our know- ledge extends, are, ift. To effect certain changes in the mafs of blood; and id. To produce animal hear. Thefe effects, though no doubt intimately connected, I fhall take the liberty of confidering feparately, for the fake of greater perfpicuity. The compofition of the atmofphere has already been defcribed, and it is at prefent only neceffary to remind the reader, that rather lefs than three -fourths of the gtmofphere is azotic gas, rather more than one fourth oxygen 33 2 Refpiration of Injefis, 6fr. [Book IX. oxygen' gas, and one or two parts in the hundred fixed air. The azote is not proved to have any effect in refpiration, and feems to be merely a diluent of the oxygen gas, which is the principal agent. The fixed air contained in the atmofphere is probably alfo com- pletely inert with refpect to refpiration. Previous to a more particular confideration of the nature of this function, it may not, however, be improper to throw together a few milcelianeous obfervations on that fubject. Animals breathing air contaminated by refpiration, not only fuffer for want of the pure part of that air, which is deftroyed, but alfo from the fixed air which is produced. Mr. Cavendifh afierts, that in certain difeafes, and by certain peribns, the air is much fooner rendered unrefpirable. According to the obfervations of Dr. Prieftley, infects appeared to breathe fixed air, or air otherwife contaminated, as readily as pure air. Flies, however, and other winged infects, have the pro- perty of deftroying the falubrity of air by their own refpiration, as may be obferved by confining a few of thofe animals in a phial. Thefe animals, indeed, appear lefs of the amphibious kind, and much more delicate, than when in the vermiform or maggot ftate. Infects, and fome exfangnious animals, will exift a confiderable time without any thing equivalent to refpiration. The fame has been proved to be the cafe with fifhes, though it is impoflible to define the limits of their exiftence. A veiTel in which, when filled with common air, a moufe could not live more than half an hour, was filled by Dr. Prieftley with vital air ; a moufe then lived in it for three hours, and being taken out alive, the Chap. 3-] Aftian of Vital Air, fcff. 333 the air was ftill found better, by the nitrous tell, than common air. From fome experiments made by Dr. Goodwyn, he concludes that the lungs contain 109 cubic inches of air after a complete expiration ; and that this quantity receives an addition of fourteen cubic inches by infpiration. The dilatation of the lungs, therefore, after expiration, is to their Dilatation after infpiration as 109 to 123. One infpiration is commonly performed for every four or five pulfations of the heart, which latter, in different healthy perfons, vary from fixty to ninety in a minute. The blood undergoes remarkable changes of co- lour when circulating in the vefifels of an animal 5 in the lungs it acquires a florid hue, which is gradually loft, while the blood is paflmg through the other parts of the body, again to be reftored in the lungs. That the red colour of blood is owing to the influ- ence of vital air is manifeft from actual experiment. Dr. Prieftley introduced different portions of Iheep's blood into different kinds of air, and found always that the blacked parts affumed a bright red colour in common air, and more efpecially in vital air; whereas the brighteft red blood became prefently black in any air unfit for refpiration, as fixed air, inflammable, azotic, and nitrous gas, and after becoming black in the laft of thefe kinds of air, it regained its red colour on being expofed to common or vital air, the fame portions be- coming alternately black and red. It is proper, however, to mention, that Dr. Good- wyn introduced four ounces of florid blood, frefh drawn, into a glafs receiver, containing fixed air, and confined it there for a considerable time ; and a]fo re- ceived blood from the carotid arteiy of a fheep into a x phial 334 Caufe of the Red Colour [Book IX, phial filled with fixed air, but in neither of the expe- riments was the florid colour altered. Thefe expe- riments do not accord with thofe of Dr< Prieftley, but the following is intirely confonant with them. Dn Goodwyn inclofed a quantity of vital air in a glafs receiver inverted in quickfilver, and introduced into it four ounces of blood, frefh drawn from the jugular vein of a ftieep; the blood became inftamly very florid; and after feveral minutes the quickfilver afcended two or three lines, xvhich evidently proved, that while the blood was altered in colour, the air was at the fame time diminimed in quantity. It is well known that blood, when it coagulates on being expofed to common air, afiiimes on the fur- face a bright red colour, while the infide is much darker, bordering upon black. An objection, however, feems to p.rife to this hy-^ pothefis, viz. that though the blood in the h;ngs is not more than a thoufandih part of an inch from the air, yet it never comes into actual contact with it. In order to examine the foundnefs of this objection, Dr. Prieftley took a large quantity of black blood, and put it -into a bladder moiftened with a little ferum, and tying it very clofe, hung it in a free expofure to the air, though in a quiefcent ftate, and next day found, upon examination, that all the lower furface of the blood, which had been feparated from common air only by the intervention of the bladder, had acquired a coating of a florid red colour, and as thick appa- rently as it would have acquired if immediately ex- pofed to the open air. — In this cafe it is evident, that the change of colour could not have been owing to evaporation, as fome have imagined. A piece of the eraffarnentuffij furrounded by ferum, acquired (ndt only Chap. 32.] of the Blood. 335 only on that part of the furface which was expofed to the air, but in thofe parts which were covered feveral inches with ferum) a florid red, fo that the deep co- vering of ferum, which muft have prevented all eva- poration, was no more an impediment to the action of the air than the bladder. That it is really the air, acting through the ferum, and not the ferum itfelf, which gives the florid colour, is clearly afcertained by the following experiment : two equal portions of black blood were put into two cups, containing equal quan- tities of ferum, which covered the blood in both to the depth of half an inch. One of the cups being left in the open air, and the other being placed under the jexhaufted receiver of art air pump, the former pre- fently acquired a florid colour, while the other con- tinued twelve hours as black as. at firft. In another experiment, the. reverfe of the former, the influence of the air upon the blood was no lefs decifively proved j for red blood became black through the depth of two inches of ferum, when the veiTel containing it was ex- pofed to azotic gas. Putiefaction, however, will pro- duce a fimilar effect ; for a frnall quantity of perfectly florid blood being put into a glafs tube fealed herme- tically, and thus cut off from all communication with external fubftances, became black in a few days. Ex- cept ferum, milk is the only animal fluid, through which the air can act upon blood. . By fome fubfe- quent experiments made by Dr. Prieftley, he found that the intervention of a bladder by no means pre- vents the action of fome airs on each other, as the ni- trous on common air, &c. The fame induftrious philofopher found alfo, that the air and blood employed in the above experiments undergo oppofite changes ; for vital air was vitiated by expofure to venous blood, and, on the contrary, inflammable- 336 Generation affixed Air in tie Lungs. [Book IX, inflammable air was abforbed, and foul air improved, by exp'ofure to arterial blood. It has alib been proved, that inflammable air will produce a change of colour in the blood, when introduced into the veins of a living animal. The moil remarkable change produced on air, which has been fubfervient to refpiration, is the difappear- ance of the vital air, and the produftion of fixed air. On account: of the production of fixed air, indeed, an animal can only breathe a given quantity of air for a certain time, after which it fickens and dies. If a jar filled with vital air is placed over mercury, and an animal confined in it, after a time it will be obferved to breathe with diincuky, and become very uneafy 5 if the animal is then taken out, and cauftic alkali is in- troduced, a great diminution in tiie bulk of the air will take place ; by the repeated introduction of the ani- mal and the caudle alkali, almoft the whole of the air may be made to difappear, which proves that the vital air is by refpiration converted into fixed air. "When we confider the compofition of fixed air, which confifts of the carbonaceous principle united with oxygen, we muft conclude that the oxygen gas is con- verted into fixed air by the addition of that principle, which, in a ftate of extreme divifion, fecfns to be ex- tricated from the lungs. By fome phyfiologifts, the extrication of this noxious principle has been confidered as the only end anfwered by refpiration. That this is not all, however, is proved by the confideration, that though part of the oxygenous gas is converted into fixed air by the audition of the carbonaceous principle, yet the weight of the air expired does not exceed that which is infpired. This naturally fuggefted the opi- nign, that a part of the infpired air was abforbed, nearly correfponding Chap. 3-2.] Water expired from the Lungs. 337 correfponding in weight with the matter difcharged by the lungs. Dr. Prieftley, by a feries of experiments recorded in vol. Ixxx. p. 106. of the Philofophical Tranfactions, has accordingly proved, that a confider- able quantity of vital air is abforbed by the blood. A very fmall portion of water is alfo thrown from the lungs at every expiration, which may be either an aqueous exhalation from the Iungs3 or may be formed by an union of vital air with inflammable gas. Mr. Lavoifier afcertained that when the air out of doors confided of, 27 parts oxygen air, 73 azotic air. ICO The air in the lowed ward in the General Hofpital at Paris, contained but 25 parts of oxygen air, 71 of azotic air, 4 of fixed air; 100 This proportion varied In different parts of the room. At the top the air contained the following proportions : i8£ parts of oxygen air, 79 of azotic air, 2f of fixed air. 100 The production of animal heat next properly claims our attention. That refpiration is really the caufe of animal heat can fcarcely be doubted j for thofe ani- ,mals which are furriiftied with lungs, rind which con- tinually infpire the frefh air in great quantities, have the power of keeping themfelves at a temperature con- Tot. III. Z fiderably 33 3 Birds hotter than other Animals. [Book 1 JG fiderably higher than the fur rounding atmofphere 5 but fuch animals as are not furnifhed with refpiratory or- gans, are very nearly of the fame temperature with the medium in which they live. Among the hot animals, thofe are the warmed whkh have the largeft refpiratory organs in proportion to the bulk of their bodies. This is particularly the cafe with birds, which have the greatefl degree of animal heat. In the fame animal, the degree of heat is in fome meafure propor- tionable to the quantity of air refpired in a given time. Thus we find, that animal heat is increafed by exer- cife and whatever accelerates refpi ration. By the word heat I do not in this -place mean a fenfarion, but calo- ric, or a peculiar fluid, having attractions for other fub- ftances, with which it is capable of forming combinations, und producing many important phenomena. We muft carefully avoid eftimating the quantity of heat or caloric contained in a body by its temperature, as indicated by the fenfes, or even by a thermometer ; for water, wax, metallic bodies, &c. in paffing from a fluid to a folid ftate, lofe a vaft quantity of heat without any diminu- tion of temperature ; and it is well known, that a quantity of wax, &c. partly folid and partly fluid, is always of the fame temperature, whether it tends to- wards the folid or the fluid ftate j that is, whatever ii the temperature of the furrounding medium. If the wax is in a melting ftate, it abforbs the fuperfluous caloric, which becomes latent ; if on the other hand ic is congealing, its latent heat is continually extricated, and fuftains its temperature at a fixed point. Caloric may therefore exifl in a latent ftate, in which it Cannot affect the thermometer. There is ffill another difference with refpedt to the quantity of heat or caloric contained in bodies, indepen- dent of any change of form, ftmilajr to. that which takes place Chap. 32;] Animal Heat. .339 place in the combination of heat with ice conftituting water. This latter difference is called a difference in ca- pacity for heat, by which is unclerftood an inequality in the quantity of abfolute heat in two bodies, though their temperatures and weights are equal. Thus, if a pound of water and a pound of diaphoretic antimony have a common temperature, the quantity of abfolute heac contained in the former is nearly four times that con- tained in the latter. The following is a brief ftatement of Dr. Craw- ford's ingenious theory of animal heat. He made a feries of experiments, by which he found, that the fixed air and aqueous vapour, which are difcharged from the lungs, contain only about one-third part of the ab- folute heat contained in the atmofpherical air, previ- ous to its being refpired: air, therefore, in becoming fubfervient to refpiration, lofes part of its heat. He has alfo fhewn that the abfolute heat of florid ar- terial blood is to that of venous nearly as eleverr and an half to ten -, fince,' therefore, the blood, which is re- turned by the pulmonary veins to the heart, has its quantity of abfolute .heat increafed, he fairly concludes that it muft have acquired this additional heat in the lungs. From the preceding obfervations it appears, that the production of animal heat depends on a pro- cefs analogous to chemical elective attraction, and which is* regulated by the following principles. Vital air contains more abfolute heat, in proportion to its temperature and weight, than fixed air. The blood is returned to the lungs impregnated with the carbona- ceous principle ; the blood has lefs attraction for that principle than vital air has ; in the lungs, therefore, it quits the blood to unite with the vital air. By this combination the vital air is changed into fixed air, and depofits part of its heat : the capacity of blood for heac Z2 is 340 J>. Crawford's Theory. [Book IX. is at the fame time increafed ; the blood therefore rc- teives that portion of heat which was detached from the air. The arterial blood,- in its pafTage through the" ca- pillary veffels, is again impregnated with the carbo- naceous principle, and the bafis of inflammable air, by which its capacity for heat declines ; it, therefore, in the courfe of the circulation, gradually grves out the heat which it had received in the lungs, and diffufes it over the whole body. Thus it appears, that in its circulation through the lungs the blood is contimfally difcharging carbonaceous matter and abforbing heat, and that in its pafiage through the other parts of the body it is perpetually imbibing carbon and emitting heat. In this account of animal heat I have entirely omitted the abforption of vital air. This abforption was not admitted by Dr. Crawford, and, though eftablifhed by the experiments of Dr. Prieftley, does not? at all invalidate the theory of the former philofopher. It is confident with either hypothefis, that the blood in the lungs gains the heat which is loft by the air ; and upon the truth of this propofition refts the theory of Dr* Crawford. By the different capacity which blood poffefles for heat in its different ftates,"it is capable of fupplying the different parts of the body with heat, while its own temperature remains the fame. If this difference of capacity for heat did not exift, the extremities of the body cpuld not be properly fupplied with heat from the lungs, unlefs the lungs themfelves were expofed to a degree of heat which would be certainly prejudicial,. and, perhaps, fuch as no organiied fubftance could fup- port without deftru&ion. Dr. Crawford has moreover proved, by a courfe of experiments, that when an animal is placed in a cold * medium, Chap. 32.] Of Animal Heat. 34! medium, the venous blood acquires a deeper hue^. that a greater quantity of air is vitiated in a given time, and, confequently, that more heat is abforbed by the blood. It appears, therefore, that nature has in this, as in many other inftances, connected the occafion with the means of ivipplying it. Since, therefore, it is proved, that heat is abforbed from the air in refpiration, and fince the quantity abforbed is not only adequate >to the purpofe, but proportioned to the occafion, we may confider ourfelves as greacly indebted to Dr. Crawford "for having thrown great light on a moft important function, but which muft ftill be enumerated, on fome accounts, among thofe obfcure proceffes of nature, on which human ingenuity may exert its powers, but which it can probably never completely reveal. The analogy between combuftion and refpiration - cannot fail to ftrike every perfon acquainted with the nature of thefe procefles. Air, in which a candle has remained till extinguished, is incapable of fupporting animal life. On the other hand, air, in which an ani- mal has remained till it expired, will not fupport the flame of a candle. In both thefe cafes heat is -loft by the air employed; becaufe gaffeous compounds are formed which have lefs capacity for heat than oxygen gas pofiefies. There is one remarkable difference, however, between combuftion and refpiration j in. com- buftion, the. heat derived from the air becomes imme- diately perceptible, and frequently rifes to an intenfc degree. In refpiration, however, the heat is gradually evolved, i.n confequencq _of an admirable law of the animal economy, which has already been adverted to in explaining Dr. Crawford's theory of animal heat. What oily and fpirituous fubftances are to a lamp they are alfo to the animal body, and no animal is Capable of fubfifting for a qonfiderable time without Z 3 food 342 Animal Heat. [Bcok IX', food containing fome portion of thefe principles. This is particularly obvious with regard to the food of carnivorous animals, and it is no lefs certain that grain and even grafs contain the ingredients of oil and fpiri- tuous liquors. Our food may therefore be confidered as fuel, and animal heat as a gentle combuftion. Hence, fuch perfons as eat and drink large quantities of in- flammable fubftances, increafe the heat of their bodies beyond the proper flandard, and in fcientific as well as common language, may be faid to burn themfelves up. This confideration may ferve to confirm the eftablilhed practice of withholding from febrile pa- tients the life of inflammable matters as food, and of giving acids, the nature of which is directly oppofite. Towards the end of fome fevers, however, particularly typhus, when the heat finks below the proper flandard, brandy and asther are found to be highly ufeful. In the Medical Extracts, in which there are fome ingenious and new obfervations on this fubject, it is mentioned that Dr. Withering wrote to Dr. Beddoes to the following effect : — The late Mr. Spalding, who did fo much in improving and ufing the diving bell, was a man of nice obfervation, and had he not fallen a facrificeto the negligence of drunken attendants, would have thrown much additional light upon more than one branch of fcience. He particularly informed me that when he had eaten animal food, or drank fermented liquors, he confumed the air in the bell much fader than when he lived upon vegetable food and drank only water. Many repeated3 trials had fo convinced him of this, that he conftantly abftained from the. former diet whilft engaged in diving. 33-] [ 343 ] CHAP. XXXIII. THE VOICE. I/iJlrament of tie Fcicc hi the Animal B ",{<;. -~ T/v Larynx.-*-Expcr:- ments on tbc Windpipes of dijj'cf -;>:t A-nm^h. — Whether the Larynx atfs as a the pro- feflbr of anatomy at Bologna, obferving one day cer- tain involuntary contractions and motions in fome frogs, which, with little credit to the profeflfor's huma- nity, had been hooked by the back-bone and fuf- pended from the iron palifadoes of his garden, his cu- riofity was powerfully excited, and on examining mi- Vou III. A 3> nutely 354 Dijcwery of Gaham. [Book IX. nutely into the caufe of thefe contractions, he found that he could produce them at pleafure, by touching, the animals with two different metals at the fame time in contact with each other. From later obfervations it feems to be fufficiently afcertained that thefe involuntary contractions cannot be excited by any fubftances whatever, whether folid or fluid, except the metals, and that the mutual con- tact of two metals with each other is, in every cafe, necefTary to the effect. Zinc has been found by far the mod efficacious, efpecially when in contact with gold, filver, molybdena, fteel or copper, although thefe latter excite feeble contractions when in contact ,. only with each other. Next to zinc, tin and lead feem to be the befl exciters. When the pieces of metals employed, and the furface of the animal fibre with which they are in contact, are large, the contractions excited are in general more confiderable, but by no means in proportion to thefe circumftances. In order to obferve the phenomena in queftion, cut off the head of a frog. When it has ceafed to flruggle, apply a plate of zinc under its body, and a plate of gold to the fuperior furface. Then Hide the gold plate ' till it comes in contact with the zinc, when the mufcles which are further from the brain and fpinal marrow than the metals, will be vifibly agitated. This effect will take place, although the frog, with the metals are placed on an inverted glafs jar, and a Hick of fealing-wax is fnterpofed between -the hand of the operator and the metals, that is, although the animal as well as the metals is infulated. I men- tioned gold as being the moft' powerful of the metals, but a plate of filver, a crown-piece for inftance, will anfwer the purpofe. Cut off the thigh of a frog, juft killed, clofe to the i body, Chap. 35.] Experiments on dead Animals. 355 body, and lay bare the fciatic nerve. Place the nerve in contact with a piece of zinc, and let its foot reft on a piece of filver ; on bringing the two metals into contact, the mufcles of the limb will be con- vulfed. If a piece of brafs wire is made to touch at the fame time the metals difpofed as above defcribed, a communication will be formed between them, and the contraction of the mufcles will equally take place. If the nerve is made to reft on a piece of zinc, and the zinc is touched with a plate of filver held in one hand of the operator, while with the other he takes hold of the foot of the frog, the influence will pafs through the body of the operator, and the limb will alfo be convulfed. — Thefe experiments muft be performed before the nerve becomes dry by expofure to the air. In order that thefe contractions mould be produced, it is not neceflary that either of the metals (liould be in actual contact with the animal in which the convulfions are to be excited ; as the interpofition of pieces of boiled or putrid beef were found by Dr. Monro not to prevent the effect. By an experiment of Dr. Fowler the fame fact is proved. He found that if a frog, of which the head mould be firft cut off, is divided into two parts, juft above the origin of the fciatic nerves, and put into a bafon of water, the hind legs may be thrown into ftrong contractions, by bringing zinc and filver into con- tact with each other, at the diftance of at leaft an inch from the divided fpine, fo long as they are kept nearly in a line with it. Water in this cafe is the only communication between the metals and the origin of the nerves. A a 2 Dr. 356 Watery Met ah ; &c. Conductors [Book D£. Dr. Fowler remarks, that he has frequently pafied this influence through a great length of thin brafs wire, and through the bodies of five perfons communicating with each other by dipping their fingers in bafons of water placed between them ; yet it did not appear to have loft any of its force in this long and diffufed paf- lage j for the contractions excited in the frog's leg were equally itrong, as when it had pafied only through one perfon. Dr. Fowler made many experiment in order to difcover what fubftances were conductors and what non- conductors of this influence. He found that all metals when pure were excellent conductors j that they were not quite fo good when in the ore ; and as far as he could afcertain, lead fo when in the ftate of metallic falts. From trials which he made with fome of the calces of metals he concludes, that in that ftate their capacity as conductors is quite deftroyed. Stones feemed to be poffeffed of no conducting power. The different non-conductors of electricity were found to be non-conductors of this influence. Living vege- tables afforded it a ready pafTage, probably from the fluids which they contain. Oils of all kinds were fo far from conducting, that if the fingers of the perfon holding either the probe or the zinc have perfpired much, even this operates as a complete obftruction to the pafTage of the influence ; the inftant the perfpired matter, has been wiped away, and the fingers have been dipped in water, it again paries and excites contrac- tions. Dr. Fowler wiihed to afcertain whether it pafied over the furface or through the fubftance of metals ; he coated feveral rods of different metals with fealing- wax, leaving nothing but their ends, by which they were held, uncovered. Contractions were excited as readily through the medium of thefe/as if they had not been coated. It feems to meet with no obftruc- tion Chap. 35.] cf Animal Ekftricity. 357 tion in paffing from link to link of feveral chains, even when no preffure, except that of their own weight, is ufed to bring them into contact. Dr. Fowler was led from this to hope, that he Ihould be able to make it pafs through a very thin plate of air* He therefore coated a flick of fealing-wax with a plate of tin-foil, and then made an almoft imperceptible divifion acrofs it with a fharp pen-knife j but even this interruption of continuity in the conductor was fufficient effectually to prevent its pafTage. Dr, Fowler next proceeds to examine whether the capacity of different fubftances, as conductors or non- conductors, was at all affected by differences of their temperature ; but this was not the caie wiih zinc, iron, water, coal, or a common crucible, the only Jubilances with which he tried the experiment. The effects of this influence may be felt in ourfelve^s by a very eafy experiment. If a piece of lead is ap- plied to the upper part of the point of the tongue, while a piece of filver is applied to the under part, upon bringing the two metals into contact, a fomewhat pungent fenfation will be felt, accompanied by aftrong metalline tafle of fome duration. The fame fenfa- tion takes place though both of the metals are pre- vented from touching the tongue by the interpofitibn of moiftened paper, Dr. Fowler fays, he could never perceive that the fenfes either of touch or fmell were in the lead affected by the rnetals ; but the effect which they produce on they eye is very remarkable. Having laid a piece of tin-foil on the point of his tongue, he placed the rounded end of a filver pencil-cafe againft the ball of his eye, in the inner canthus, and fuffered them to re- main in thefe fituations till the parts were fo accuftomed $Q them, that /he could examine the fenfations pro- A a 3 duced \ 3 5 * Experiments relative [B ook IX. duced; he then brought the metals 'into contact with each other, and, to his furprife, perceived a pale flam of light diffufe itfelf over the whole of his eye. His tongue was at the fame time affected with a fimilar fenfation to that produced when both of the metals are in contact with it. On darkening the room the flafti became more diflinct and of a ftronger colour. If the experiment is made with zinz and gold, inftead of tin- foil and filver, the flam is incomparably more vivid. By infmuating a rod of filver as far as poffible up the ncfe and then bringing it into contact with a piece of zinc placed upon his tongue, he alfo fucceeded in pro- ducing the fenfation of a flam of light, rather more vivid than when the filver was in contact with the ball of the eye. Dr. Fowler alfo mentions that his friend, Mr. George Hunter of York, difcovered that by placing one of the metals as high up as poflible be- tween the gums and the upper lip, and the other in a fimilar fituation with regard to the under lip, a flafh was produced as vivid as that occafioned by paffing one of the metals up the nofe, and placing the other upon the tongue. It differs, however, from the flam produced in the other way, in the fingular circumftance of not being confined to the eye alone, but appearing diffufed over the whole face. On repeating the ex- periment myfelf, and attending to the concomitant fenfations produced by this difpofition of the metals, I perceived that a fenfe of warmth, at the inftant that they were -brought into contact, diffufed itfelf over the whole upper furface of the tongue, proceeding from its root to the point. Dr. Rutherford, to whom Mr. Hunter had communicated this experiment, remarked, on repeating it, that a flam is produced not only at the inftant the metals are brought into contact, but like- •wife at the inftant of their feparation i while they re- main Chap. 35.] to Animal Eleftricity. 359 main in contact no flaih is obferved. Thefe curious phenomena demonftrate the free communication which fubfifts. between the feveral branches of the fifth pair of nerves. The following curious fact is alfo taken from Dr. Fowler's ingenious and entertaining book on animal electricity. He laid a leech on a crown-piece of filver, placed in the middle of a large plate of zinc. The animal moved its mouth over the furface of the filver without expreffmg the leaft uneafmefsj but having ftretched beyond it and touched the zinc plate with its mouth, it inftantly recoiled as if in the moft acute pain, and continued thus alternately touching and recoiling from the zinc, till it had the appearance of being ex- tremely fatigued. When placed wholly upon the zinc, it feemed perfectly at its eafe ; but when at any time its mouth came in contact with the filver lying upon the zinc, the fame expreffion of pain was exhibited as before. With the earth-worm he found that the ex- periment fucceeded flill more decifively. The animal fprang from the zinc in writhing convulfions ; if, when the worm ftretched itfelf forwards, one of the folds came upon the zinc, it expreffed little uneafmefs in eomparifon of what it fhewed when the point of its head touched the zinc. Whether this influence, whatever it may be, is de- rived from the metals alone, or whether the animals contribute to its production, is not eafy to determine. On re-confidering the phenomena exhibited by this newly difcovered influence, we mail perceive that in fome refpe£ts it remarkably refembles electricity, and in others as remarkably differs from it. Like the electric fluid, it ftimulates mufcles to con- traction. Like that, its progrefs is arrefted by glafs, lealing-wax, Sfc. while it is conducted by metals, A a 4 moifture, 360 Analogy between this [Book DC, moifture, &c. Dr. Valli informs us, that he obferved the hairs of a moufe, attached to the nerves of frogs by the tin-foil with which he furrounded them, alter-* nately attracted and repelled by each other, whenever another metal was fo applied as to excite contractions in the frogs. Like the electric fluid, it excites a fenfation of pungency in the tongue ; and paffes with fimilar rapidity through the bodies of animals. It differs from the electric fluid in many refpects. In order to excite the electric power, it is neccffary that there fhould be motion or friction between two fubftances, an electric and a conductor. Animal electricity is produced by two metals, which are both conductors and without friction. According to Dr. Fowler, charcoal is a better con- ductor of electricity than the fluids of animal bodies. Whereas he never could make the influence in queftion pafs through charcoal. Dr. Fowler in oppofition to Dr. Valli alledges, that he could not obferve that the niceft electrometers were affected by this influence. The fame author remarks, that the moft important and characteriftical difference which he has yet been able to djfcover between this new influence and electri- city, confifts in their effects upon the contractile power of animals and of plants. The contractions of animals excited by electricity, have a tendency to deftroy that power upon which contractions depend. But the contractions excited by the application of the metals, have in all his experiments had the directly oppofite effect. The rrore frequently contractions have been in this way excited, the longer they continue excit- able ; and the longer are the parts upon which fuch experiments are made, preferycd from putridity. It Chap. 35.] Influence and Eleffricity. 361 It is faid that aftream of electricity patted tjirough a fenfitive plant, produces an almoft immediate col- lapfe of its leaves; but the influence in queftion produced no fuch effe6t in an experiment made by Dr. Fowler. The fame attentive experimentalift electrified both pofitively and negatively frogs, whofe heads had been ieparated from their bodies. In thefe circumftances the effects of the influence in queftion took place in the fame manner and degree as when no artificial elec- tricity was prefent. When there is a breach of equilibrium in the diftribution of the electric fluid, all that is required in order to reftore the equality of diftribution, is the interpofition of a fmgle conducting fubftance between the place in which it abounds, and that in which there is a deficiency ; whereas if the phenomena of animal electricity are to be attributed to the fame caufe, it does not appear why two conducting fubftances fhould be neceffarjr. In eftablifhing a communication between two op- pofite electricities, as, for example, between the two fides of a charged phial, it is matter of indifference to which the conductor is firft applied ; but it is by no means fo, in producing the phenomena of animal electricity; for if one branch of a conductor is applied to the tin-foil arming a nerve, before the other branch has been applied to the mufcles, it frequently fails to excite contractions. If firft applied to the mufcles, this is very feldom the cafe. From fome trials which Dr. Fowler made with the artificial and natural loadftones, and a -very fenfible magnetic needle, he faw no reafon to fuppofe that this new influence was in any way connected with magnetifm. Animal Animal Elettricity. [Book IX. Animal electricity is even found to differ, in Tome refpects, from that power by which the torpedo, gymnotus, &c. produce their Ihocks. We are told by Mr. Cavendifh, that Mr. Walfh found that the ihock of the torpedo would not pafs through a fmall brafs chain. It. refembles the power of the torpedo, however, in producing its effects almoft equally well, •when both it and the fubject upon which it acts are infukted from furrounding conductors. The ihock of the torpedo, &c. feems to depend entirely on the will of the animal j but the will of the animal has no fhare in the production of the phenomena difcovered by Galvani. That this influence is not the fame with the ner- vous energy appears from its not being flopped by a tight ligature, or by the tranfverfe ineifion of a nerve, provided its parts are again brought into dole contact. The nervous energy is effectually flopped by a tight ligature or a tranfverfe incifion j and placing the divided extremities into the clofeft contact, has no effect in reftoring its influence on the parts of the body to which the divided nerve was diftributed. On the whole, it may be remarked, that the influ- ence difcovered by Galvani refembles electricity more than any other known law of nature. But it differs in fo many inftances even from it, that in the prefent flate of our knowledge, we muft confider it as a newly difcovered law in nature; though future experience and more extenfive obferyation may lead to a different; conclufion. Chap. 36.] CHAP. XXXVI. S E N S A T.I O N. Difficulty of the Subjeft. — Senfationtbe Effeft of certain Relations ejla- blijhed by the Creator.— Objefts of different Senfes. --^Influence of ike Nerves in conveying Senfations to the Brain.'— The Brain the Repo- Jttory of Ideas. — InJliniJ of Animals as connected with the nervous Syftem. — Harmony of the Senfes. — Duration offenfiblelmprejfions.— The Five Senfes. FROM the confideration of the other functions to that of fenfation, the tranfition muft be ab- rupt and without gradation. We now enter on a fubject above all others the moft intricate and difficult, and on which, fince reafon is engaged in difcovering the fource whence it derives thofe ideas on which it acts, we muft neceiTarily reafon in a circle. Senfation is the link by which the Deity has con- nected the material to the immaterial world. With- out fenfation, in vain would the ftars have beipangled the firmament of heaven, in vain would that glorious object the fun have been appointed to illuminate and cherifh the productions of the earth j they could have been nothing to beings who muft have been un- confcions even of exiftence : and the material world would have been a work without utility or defign. Senfation is the confequence of certain eftablimed relations between objects j of thefe relations we can give no account, for they appear equally above our comprehenfion with the principles of gravitation, electricity, or magnetifm. Relations between the matter of light, the objects of vifion, and the eye, produce 364 Relation between external [Boo produce fight ; delations between certain vibrations of the air and the fenforium of the ear produce hearing, and fo of the other fenfes. We by no means, how- ever, can pretend, in. any of thefe cafes, to deter- mine all the intermediate caufes and effects between the quality in a body, which renders it an object of fenfation, and the perception in ourfelves ; nor are we by any means authorized to 'conclude, that our per- ceptions are juft emblems of the objects which occa- fion them. But this circumftance, upon which fo much has been faid, can be to us of little im- portance, fince it ftill remains equally true, that our fenfations are regulated by fixed laws eftablifhed by the Deity himfelf, and fince we mull fuppofe that the Creator of the nniverfe has ordered all things in wif- dom and goodnefs. We are ignorant of the means by which the objects of fenfation affeft the body ; but the moft obvious and fimple idea that we can form on this fubject is, that they act by impulfe. Thus the rays of light are known to travel with aftonifhing velocity, and to pofiefs a power of moving light bodies. Sound is a tremulous motion of the air, capable of being com- municated to bodies in harmonic proportion with it. Odorous particles require the affiftance and motion of air to affect the organs of fcent. The objects of tafte are more perfectly perceived by being prefled between the tongue and palate. In order to feel any thing, it is neceflary that the fkin mould be prefled againfl it with a certain degree of force, or, what is Hill more, effectual, rubbed over its furface. The inilruments, which are defigned to convey the effects produced by material objects on the organs of lenfation to the brain, are the nerves, which have been already defcribed as diftributed to the feveral parts of £hap. 36.] Objefts and our Senjes. 365 of the body, and more particularly to the organs of fenfadon. What is the difference of ftrudture, which adapts the feveral nerves to the federal organs of fen- fation} we know not, nor can we determine whether certain parts of the brain correfpond with the nerves connected with certain organs of fenfation, and are deftined to preferve the ideas received by thefe parti- cular organs, or whether the whole brain is common to the whole flock of our ideas and fenfations ; though thefe have been fubjects of 'much Speculation, it has not even yet' been ascertained, whether any material imprefiion whatever takes place in the brain in confe- quence of imprefiions on our fenfes j and until this queftion is determined, we cannot be prepared to ex- amine the other. That the brain, however, is really in fome way or other the repoficory of our ideas, we may venture to conclude, fmce a perfon who lofes an organ of lenfation does not lofe the ideas previoufly acquired by it ; and fmce perfons fometimes comphin of pain, feated in the extremity of a limb of which they have longTince been deprived. There have been of late years fome curious {pecula- tions among philofophers with refpect to the material caufe of inftinct in animals, and as there is fome plaufibility in their reafonings, it may be worth while briefly to mention the outlines of their fyftem. They fuppofe that the motions of animals, commonly called inftinctive, arife from a connection of the nerves be- longing to different parts in the brain. In this man- ner, when the young bird hears the call of its mother, and opens its beak, they fuppofe this effect to be owing to an original connection between the auditory nerve and the nerves communicating with the mufcles em- ployed in opening the bird's beak. When a new-born quadruped performs the complex action of fucking, in con- 366 SenfiUe Impreflions mot evanefcent. [Book IXi colifequcnce of the application of its nofe to the teat of its mother, they attribute its capacity for executing a function, in which fo many mufcles are employed, to a connection originally exifting between the nerves of its nofe and thofe which belong to the organs em- ployed in fucking. The moft complex inftinctive actions of animals, according to thefe philofophers, may be explained on the fame hypothefis. The qualities of bodies, as perceived by one fenle, are very frequently connected with others perceived in the fame bodies by the other fenfes : thus, apparent uncvennefs of furface, is united with a roughnefs to the touch ; apparent vibration, with found ; and there is a certain analogy between the odours and taftes of many bodies. Thefe conclufions, however, are to be referred to our previous experience, and by no means authorize us to think that there is any fimilitude in the mode of perception between the fenfes of feeing and hearing, feeing and feeling, or tailing and fmelling. It is faid, that there have been perfons who could diftin- guifh colours by the fenfe of feeling j but if they did, it muft evidently have been from fome difference of roughnefs, fmoothnefs, &c. refulting from the mate- rials employed in colouring, and not from any pro- perty inherent in the different colours as objects of fight. It is ordained by our Creator, for the moft impor- tant purpofes, that our fenfations mould not be too evanefcent j and it requires fome time after one im- prelTion is made on an organ of fenfe, before that organ can receive another. This is proved by a very fimple and decifive experiment. All of us h&ve probably obferved, when a ftick lighted at one end, or a coal, is whirled round with a certain degree of velocity, that the whole circle which it performs appears equally illu- minated, Chap. 36.] ttc Powers of Senfation limited. 367 minated, and that we cannot determine at what point of the circle the fire really is, and the fame circum- flance may be obferved in the blending of colours, which are yet marked diftinctly on a wheel before it is turned. The evident caufe of thefe appearances is in the eye ; and in the firft cafe, when we fix our eye on any point of the circle made by the evolution of a lighted coal, the illuminated object again returns to that point before the fenfation previoufly produced is worn off: and the blending of the colours on a wheel is explained in the fame way ; for the impreffion made by one colour remains till the other arrives and mixes with it. It is alfo well known, that perfons who have the beft and quickeft ears for mufic cannot judge ac- curately of more than a certain number of notes in a fecond of time. Innumerable fads, indeed, may ferve to convince us, that the mind cannot well attend to two or more fenfations at the fame time *. Hold your tongue, faid a Frenchman, you talk fo I cannot tafte my meat. The Frenchman was certainly right ; for attention of mind is not lefs necefiary to full percep- tion, than a healthy ftate of the organ of fenfe. All authors are agreed, that our knowledge of ex- ternal objects is entirely acquired through the medium of fenfation, though fome perfons of the higheft rank in literature and philofophy ftill contend, againft Mr. Locke, in favour of theexiftence of certain innate and * The contemptible vanity of Caefar, in pretending to perform feveral mental operations at once, proceeded from a real igno- rance of the human mind. The reply of the juftly celebrated penfionary De Witt was much more judicious, and ought to be imprefled on the mind of all young perfons. On being afked how he contrived to tranfadt fuch a multiplicity of bufmefs in the courfe of a day without negleft or difordcr, he anfwered, " I make it a rule always to attend to one object at. a time." inftinctive ?be Five Senfes. [Book IX. inftinclive principles ; but if I was difpofed to enter into the difpute, this would not be the proper place. The fenfes are five in number: touch, tafte, fmelling, hearing, and fight. Of thefe I fhall en- deavour briefly to treat in their order. I have in general confidered it as more conducive to perfpicuity, to feparate the anatomical defcription of the organs from the functions to which they are fubfervient ; but as the organs of fenfation are fmall, and at the fame time not much connected with the great outlines in the^rudure of the body ; and as the organs of fome of the fenfes, particularly that of hearing, are complex, and very difficult to be retained in the mind, I have, in this inftance, thought u neceffary to depart from the former arrangement. 37.] [ 369 ] CHAP. XXXVII. TOUCH, AND ITS ORGANS. T'/je moft exienfive of the Senfes,—- Organs of Touch.-*- In "what Mart" ner it enables us to judge of the Qualities of Bodies,— Towng Man couched by Chefclden.-— Remarks on his Cafe. IN order to protect the body from injury, almorl every part of it is fo formed as to give warning to the mind when any thing injurious affails it. The whole body may therefore, in the moft extenfive fenfe of the word, be deemed an organ of touch. The in- ternal parts of the body, however, though they are capable of feeling, yet convey no other idea but that of pain, and give us no information with refpect to the nature of what is applied to them. The furface of the body is endued with a much more extenfive power, and informs us of feveral qualities of matter ; but the lips, the tongue, and, above all, the fingers, afford us the moft accurate information of thofe qua- lities of bodies which are the objects of this fenfe. When the epidermis is removed from the true fkin, we obferve fmall obtufe papillae, which feem to be the parts which more particularly receive the impref- fions of external objects. Thefe papillse are fome- what more remarkable in the (kin at the ends of the fingers, and here we may perceive, that they have nerves, though from the extreme minutenefs of them they are hardly obfervable. We judge of heat and cold from the object being hotter or colder than our fingers * ; of the weight of a' body, from its degree * The tongue is a more nice teft of the warmth of a body than the fingers, for we can feel a warmth at the larger end of an egg with the tongue, which is not perceptible by the fingers. VOL. III. B b of 370 Young Man couched ly Chefelden. [Book IX. of prefiure compared with its bulk ; of its moifture, by its coldnefs, or the prefence of water ; of its foft- nefs, by its yielding ; of its hardnefs, by the yielding of the finger; of its figure, by applying our hands to its different parts ; of diftance, by comparifon with what we know to be the length of the finger, hand, or arm. All our conclufions, however, are fo regu- lated by previous experience, and we fo feldom trull to the evidence of touch without alfo calling in the afliftance of vifion, that without the latter fenfe the conclufions drawn from the other would be very li- mited and imperfect. Touch is the fenfe by which •we acquire a knowledge of the diftance of objects, which, independent of experience, obtained by means of this fenfe, Is not to be difcovered by vifion. This circumftance was beautifully illuflrated in the cafe of a young man, as- dated in Chefelden's anatomy. This young man, born blind, and being fuddenly enabled to fee, in confequence of a furgical operation, imagined that every thing he faw touched his eyes, and it was only by repeated trials of the diftance of objects, by means of touch, that he was taught to correct his .error. From this fact, however, it is not perfectly evi- dent, that an infant, born with all its fenfes perfect, would naturally conclude that the objects of vifion touched its eyes. Might not the young man, from being fo accuftomed to judge of objects by their feel, or by applying them to his tongue or nofe, have ac- quired the idea, that nothing could be perceived which was not in contact with the body ? and thus the con- clufion which he drew might really depend on the affociation of ideai Chap.38.] CHAP. XXXVIII. TASTE, AND ITS ORGANS. The Tongue the Organ of Tafte.—Defcriptinn of it.-—Hofw fupplied 'with Nerws.—Mu/cIes of the Tongue.— HO-VJ Rafting is ftr- farmed. TH E tongiie has been already cafually mentioned as in fome refpeds a very accurate organ of touch ; but the fenfe to which it is more particularly fubfervient is that of tafte. The palate is commonly considered as the organ of cade -, but this is a vulgar error, for unlefs the fubftance applied to the palate has fome degree of acrimony, no frnfadon whatever is the conrequence. The tongue, and more particularly at the point, and the fuperior and the lateral parts of it, is the true organ of tafte. The fkin, with which the tongue is covered, is remarkably foft and thin, and is continually preferved moid and warm. On the fur- face of this fkin papilla, much larger than in any other part of the body, and of feveral forts, are ob~ fervable. The-firft kind are few in number, arid arc placed at the back part of the tongue. Thefe are fur- rounded with a fmall furrow, and their form is almoft that of an inverted cone. They are not of a very delicate ftructure, nor are they much concerned in tailing. The fecond kind, which are fn.ialler and fofter than the preceding, and into which the firft gra- dually degenerate, have fomewhat of the form of a mufhroom j they are fcattered on the fuperior furface of the tongue, till, becoming more numerous towards its fides, they are there diftributed in diverging lines. The third kind are of a conical form, are mixed with the other kinds, and are very generally diftributed B b 2 over .37 2. *fbe Tongue tie Organ of arifon between this Senfe and that of cfafte. AS one principal ufe of the organs of fmelling is to aflift animals in obtaining proper food, and to guard them againft what is improper, they are univerfally placed near the mouth. The organs of fmell differ, like thofe of the other fenfes, according to the deftination of the animals to which they be- long. This fenfe in man is far lefs acute than that of many other animals j thus, the dog poflefles a power of fmelling, of which we can fcarcely form a concep- tion, and which we happily do not poflels. Birds of prey, however, are faid to have the fenfe of fmel- ling {till more acute than dogs. The fenfe of fmelling in man is fuch as to fit him for deriving enjoyment from a diverfity of fcents, particularly thofe of flowers, to which dogs and other animals, which do not feed on herbs, feem perfectly infenfible. The organ of fmell is a foft/vafcular, porous mem- brane, furnifhed with papilke, which is fpread on the internal furface of the noftrils. On this membrane are diftributed a great number of nervous fibres, which proceed chiefly from the firft pair of nerves, and which pafs through the ethmoid bone. From the extreme tenuity of the epidermis, which involves the nerves and blood- vefiels in this membrane, he- B b 3 morrhagc 374 Sympathy with the Organ of. XLI. SIGHT. Dejcription of the Eye. — Eyes of different Animals.— How Vifion is performed. — How all the Parts cf an Oljeft are comprehended by the Eye. — An Image of every Qbjeft painted on the Retina of each Eje, and yet only one Objtfl perceived. — Caufe and Cure of fquinting.-*- T'he Senfe of Sight limited.— By what Means we judge of Dijlance. • — State of the Sight at dijj'erent Ages.—Cautiovs for prefer-uing the Sight. TH E eyes, thofe exquifite organs which raife the perceptive powers of the mind to fome compa- rifon with thofe of fuperior beings, and which in an inftant of time admit impreflions from an almoft infinite variety of objects, are in their ftruclure extremely fimple. They are fituated in two cavities, the or- bits, which afford them protection from a great variety of external injuries, and contain a quantity of fat, which anfwers the purpofe of a foft cufhion, on which they may reft, and perform their different motions with eale and fafety. The globe of the eye is immediately covered by the eyelids, which are continuations of the common integuments of the body, doubled inwards, and attached to the eye, by which they produce what is called the tunica conjunctiva. Where the two eye- lids are united together, they form the canthi, or angles of the eyes ; that next the nofe is called the in- ternal large or inferior angle ; the other, on the con- trary, which is next the temples, is called the external fmall or fuperior angle. The edges of both eyelids are furnifhed with rims of cartilage called the tarfi ; on the margins of thefe, which are called eiliary edges, are fituated febacious glands, which diicharge an orly fluid for the purpofe of preventing adhefion. The 2 ciliary Chap. 41.] Structure of the Eye. 385 ciliary edges of the tarfi are furniihed with eye-lafhes. The chief life of thefe feems to be, to prevent duft, and other matters floating in the atmofphere, from fal- ling into the eyes. At the internal angle of the eye is fituated the ca- runcula lachrymalis, which is a fmall reddilh oblong body. This fubftance feems to be glandular. By the aid of a microfcope we obferve upon it a great number of fmall hairs, covered by an oily yellowirti matter. Oji the globe of the eye, near this glandular body, is a lemilunar fold formed by the membrana conjunctiva. This fold, which is called the membrana femilunaris, is fhaped like a crcfcent, the two points of which anfwer to the puncta lachrymalia, which are the be- ginnings of a canal terminating in the cavity of the noftrils. The furface of the eye Is conftantly moiflened by a very fine limpid fluid, the tears, which are chiefly, and perhaps wholly, derived from a gland; fituated in a fmall depreffion of the os frontis, near the external angle of the eye. Its excretory duels pierce the tunica conjunctiva ju'ft above the cartilagi- nous borders of the upper eyelids. As this fluid enters the eye at the fupterior angle; it naturally defcends towards the inferior, and is alfo frequently fpread over the furface of the eye by the motion of the eyelids. When it arrives, after thus having wafhed the eye, at the internal angle, it is conducted by the membrana femilunaris into the punfta lachrymalia, which lead into the facchus lachrymalis, from which it is ultimately difcharged into the nofe. When the eye is irritated by any extraneous fubu fiance, the tears are difcharged in greater quantity, and thus ferve as a defence to this tender organ, and fome- times wafh away the caufe of irritation, or facilitate its VO.L. JIL C « ttmoval, 336 ¥be external Coats of the Eye. [Book IX. removal. Affections of the mind allb fomctimes occa- fion an increafed flow of tears j the efficient caufe of this connection we cannot trace; but the final caufe feems to be to excite fympathy, and urge the unfeeling heart to acts of mercy and benevolence. The ball of the eye is a cafe of a globular form. It confifls of three coats, an external one called the fcierotica, which is white and gliftening like the ten- don of a mufcle; an intermediate one, abounding with blood-veflels, called the choroides; and an internal coat, called the retina, which is an extremely tender film or network, formed by the expanfion of the optic nerve. This defcription, however, applies only to the poftcrior and lateral parts of the eye, for at the lore part of the eye, inftead of the opake tunica fclerotica, we obferve a projecting tranfparent circu- lar part, continued from the fclerotica, which from its fubftance being tranfparent like horn, is galled the cornea. This portion is fomewhat more convex than the - fclerotica, and reprefents the fegment of a fmall fphere added to the fegment of a greater, or, to ex- prefs the fame idea in more familiar language, it may be .confidered as refembling a convex watch-glafs, .fixed on the lefs convex furface of a watch cafe. The tunica choroides extends from the back part of the' eye as far as the termination of t^e- fclerotica, where it is firmly connected by means of a white ring projecting inwards, and called the ciliary circle or liga- ment. From this edge proceeds a very fine weblikc membrane or curtain, called the iris. Its difference of colour in different perfons is a matter of common ob- fervation. In the middle of the iris is an. opening which always appears black, and which is rendered nar- rower or wider by the contractile powers of the iris. This opening is called the pupil, through which the ravs Chap. 41.] The Iris and Pupil. 387 rays of light are admitted to the internal parts of the eye. The tunica choroides is defcribed by fome authors as confifting of two laminas. This defcription, how- ever, applies much better to the eyes of fome animals, particularly to thofe of fheep, than to thofe of man. Thofe who fuppofe the choroides to confift of two laminae, defcribe the external one as terminating at the ciliary ligament, and the internal one as extending further to form the iris. This iris itfelf is defcribed as confifting of two laminas, and it is very certain that two fets of fibres may be obferved, Thefe are fup- pofed to be mufcular, and from the mobility of the iris there feems no reafon to doubt of their being really fo. Some of the fibres are orbicular, and lie round the pupil j others are ftrait, and extend from the cir- cumference of the iris to its center. The iris has mo- tions of fuch a nature, that the pupil is contracted on the approach of a ftrong light, and is dilated in pro- portion as the light is lefs vivid. By this admirable yet fimple contrivance, the eye adapts itfelf to the dif- ferent proportions of light to which it is expofed. If the pupil was always as much contracted as it is when expofed to the light of noon day, a weaker light, fuch as that of the moon, could not be admitted with fufficient freedom to anfwer any ufeful purpofe. On the contrary, if the pupil was immoveably dilated, w£ might take advantage of the fcattered rays of light, but Ihould be diftrefTed and blinded by the glorious effulgence of the mid-day fun. When a flrong lightv fucceeds to darknefs, we are under a neceffity of doling the eye-lids, or of turning away the head, till the pupil has been accommodated to the change by the con- tractile powers of the iris. The choroid coat is internally covered with a flimy C c 2 fubftanc? 388 Pigtwritttm, Iris,&c. [Book IX, fubftance of a dark colour, called the pigmentum ni- grum. The epithet black, however, is not defcriptive of this fttbftsnce in every race of animals. On the con- trary, in the ferret the pigmentum is white, and this cir- cumftance enables that animal to fee in the dark, a faculty well adapted to its habits and mode of life. In man, diftinct vifion in a full light is a more ufeful quality than the power of diftinguifhing objects where the light of day is excluded. The feafon, therefore, of the black colour of the pigmentum is, probably, that thofe rays which pafs the retina, which is a fibrous' fubftarice, may be abforbed, whereas, when it is of a light colour, many of them are reflected and ftrike the retina, thus increafing the power of vifion where there is a deficiency of light, but producing too great an effulgence and glare in ordinary cafes. This reflection is very obvious in the degree of illumination which proceeds from the eyes of a cat in a dark place *. The poflerior part of the iris is of the colour of a grape, and was therefore by the ancknts called the uvea. The eye, being, therefore, every where pro- vided within, except at the entrance of the optic nerve, with a lining of a dark colour, becomes a camera ob- fcura, and the light which is admitted through the pupil, and pafles to the bottom of the eye, is not dif- turbed with light reflected from other furfaces. The ball of the eye is filled with three fubftances, yrmch differ from each other in confidence, but are all called humours of the eye ; they are the vitreous,, the cryftalline> and the aqueous. See plate xv. fig. i> and 2, : * Hunter on the pigmentum of the eye. See his Aniraal ' The Chap. 41.] Humours of the Eye. , The vitreous humour was fo called from a fuppofed refemblance to melted glafs ; It is a clear and gelatinous fluid, very much refembling the white of an egg It fills about three fourths of the globe of the eye, ancj extends from the pofterior part of the eye as far as the ciliary ligament. It is contained in a fine tranfparent capfule or membrajie, and being dexteroufly removed from the globe of the eye, prelerves its confidence for ibine time, being fupported by its capfule, but after- wards runs off, and the capfule ilirinks by degrees. The thin capfule which furrounds the vitreous humour fends off a number of membraneous procefies into the vitreous fubftance, where they form cells, which com- municate with each other, and afford a greater degree of firmnefs and tenacity to the whole mais. The anterior part of the vitreous humour is exca- vated for the reception of the crydalline. This body has the confidence of very firm jelly, and has the form of a lens more convex behind than before. It is moft properly denominated the cryftalline lens, and is in- veiled with a capfule, which is derived from that of the vitreous humour, or at lead connected with it. Steno pbferved, that the lens was compofed of concentric lamellas, and Zinn has difcovered radiated ftreaks of a pearl colour, dividing it into little triangles. The colour and confidence of the cryftalline humour varies at different ages. Till the age of thirty it is very tranf- parent, and alrnoft without any colour. It after wards becomes yellowiih, and that yeilownefs gradually in- creafes. Till the age of twenty the confidence of the Jens is generally uniform throughout ; from this time it becomes hardeft in the middle, and tju's hardnefs gradually increafes, and extends towards the furface *. The * The cryftalline lens in fifh is completely fpherical, and is fnorc denfe than, in terreftrial animals. This difference is to be C c 3 accounted 390 Peculiarities in the Eyes [Book IX, The fore part of the eye is filled by a fluid tranf- parent like the others, but as thin as water, and it is therefore called aqueous ; this occupies all the fpace between the cryftalline lens and the prominent cornea. The iris floats loofely in this fluid, and divides it into two parts called chambers, which communicate with each other through the pupil. The pofterior chamber is that fpace contained between the pofterior furfacc of the iris and the lens ; the anterior is that between the anterior part of the iris and the cornea. The eye receives its blood from the internal carotid artery. The optic nerve does not enter it immedi- ately behind the pupil at its pofterior part, but rather towards the nofe, fo that the diftance between the pupil and optic nerve is greater when meafured round the external fide of the eye next the forehead, than when the internal furface is meafured next the nofe. At that part of the eye where the optic nerve enters, no fenfe of vifion can be excited. The mufcles of the eye have been already defcribed jn another part of the work. For the human eye, fee Plate XV. Fig. i, and 2. The father of the prefent Dr. Monro, of Edinburgh, has publifhed, in his comparative anatomy, fome excel- lent remarks on the variety in the eyes of different ani- mals, thnn which no more ftriking inftance can be pro- duced of the wifdom and defign which pervades creation. f All quadrupeds have, he obferves, at the internal canthus of the eye, a flrong firm membrane with a accounted for from the different refractive power of the medium in which they live. The rays of light, in pafling out of one me- dium into another, undergo a refraction proportioned to the dif- ference^of their denfities. As water, therefore, is a more denfe medium than air, the eyes of fuch animals as inhabit the former muft have a greater refraftive power than thofe which live in the latter, for the produ&ion of diftincl vifion, car- Chap. 4i •] °f 'different Animals. 391 cartilaginous edge, which may be made to cover fome part of their eyej and this is greater or lefs in differ- ent animals, as their eyes are more or lefs expofed to dangers in fearching after their food. This membrana niffitans, as it is called, is however not very large in all thefe animals. Cows and horfes have it fo large as to cover one half of the eye like a curtain, and at the fame time it is tranfparent enough to allow abundance of the rays of light to pals through it. Fifties have a cuticle always over their eyes, as they are ever in danger in that inconftant element, the water. In this there- fore we may obfeYve a fort of gradation. ' All quadrupeds have a feventh mufcle belonging to the eye, called Jufpenforius. It furrounds almoft the 'whole optic nerve, and is fixed into the fclerotic coat as the others are, Its ufe is to fuftain the weight of the globe of the eye, and to prevent the optic nerve from being too much ftretched, without obliging the four ft rait mufcles to be in a continual contraction, which would be inconvenient: at the fame time this mufcle may be brought to affift any of the other four, by caufing one particular portion of it to act at a time. c The next thing to be remarked is the figure of the pupil, which is different in different animals, but al- ways exactly accommodated to the creature's way of life, as well as to the different fpecies of objects that are viewed. Man has it circular, for obvious reafons : an ox has it oval, with the longeft diameter placed tranfverfely, to take in a larger view of its food : cats, again, have theirs likewife oval, but the longeft dia- meter placed perpendicularly ; they can either exclude a bright light altogether, or admit only as much as is neceflary^ The pupil of different animals varies in \videnefs, according as the internal organs of vifion are more or lefs acute : thus cats and owls, who feek their C c 4 prey 392 F-SJ of different Anwmls. fBook IX. prey in the night, or in dark places (and confequently rrmft have their eyes fo formed as that a few rays of light may make a lively impreffion on the retina), have their pupils in the day-time contracted into a very nar- row fpace, as a great number of rays would opprcb their nice organs ; while in the night, or where the light is faint, they open the pupil, and very fully adir.it the rays. In the fame way, when the retina is in- flamed, a great number of rays of light would occafion a painful fenfation ; therefore the pupil is contracted : on the contrary, in dying people, or in a beginning amaurofiSj it is generally dilated, as the eyes on fuch cccafions are very difficultly affected, and in fome meafure infenfible. See Plate XV. Fig. 3,4, 5. e The pofterior part of the choroid coat, which is- called tapetum, is of different colours in different creatures. For oxen, feeding moftly on grafs, have this membrane of a green colour, that it may reflect upon the retina all the rays of light which come from the objects of that colour, while other ray.\ are ab- forbed : thus the animal fees its food better than it does other objects. Cats and owls have their tapetum of a whitiih colour ; and for the fame reafons have the pupil veiy dilatable, and their organs of vifion acute: and we mail find, that all animals fee more or lefs dif- tinctly in the dark, according as their tapetum ap- proaches nearer to white or black colour. Thus dogs, who have it of a greyim colour, diftinguifh objects better in the night than man, whofe tapetum is dark brown, and who, I believe, fees worfl in the dark of any creature; it being originally defigned that he mould reft from all kinds of employment in the night time. The difference then of the colour of the tapetum, as indeed .the fabric of any other part in different creatures, always depends on Ibme particular advantage accruing to Chap. 41-3 S**fi of 'Sight. 393 to tlie animal in its peculiar manner of life from this Angularity *.' It was neceffary, in a former part of this work, to notice the fubjecl: of vifion, in defcribing the effects and phenomena of light f. The eye was then men- tioned as a mere optical inftrument, but after the par- ticular defcription of that organ, which has now been given, a more particular inveftigatian of the ienfe of fight feems to be required ; and ihould the reader find any thing like repetition in what \\t-ill now be fubmitted to him, his candour will, I doubt not, pronounce my apology for endeavouring to render as clear as pofiible a fubjeet which is at once both important and difficult to be underftood. It has been fumdently explained, that from every point of a vifible object the rays, or rather pencils, of light are emitted or reflected in every direction j t>ut to produce vifion, it is neceffary that they fhould be concentrated or converged to a fuch point as to make a forcible impreffion on the retrna. Thus from the luminous body A (Fig. 6.) the rays r} r, r are fent in various directions. Thofe which fail upon the tranf- parent cornea C C are there refracted in fuch a manner as to enter the pupil at p, and in pafiing the cryftalline lens or humour they fuffer a fecond refraction, and are converged to a point or focus at the point a on the re- tina. Now it is evident, that if the rays could have pafled the humours of the eye in their natural direction, that is in the direction of the cone or pyramid C, A, C, they would have made upon the retina a very exten- sive but feeble impreffion, fuch as we know by expe- rience could not produce diftinct vifion ; to obviate this * Monro's Comparative Anatomy, f -See book iii. chap, 7. Of Sight, [Book IX. it is appointed by the all- wife author of our exiftence, that by the force of the refraction which they fuffer in the eye, they fliould form another cone oppofed to the fcrft at its bafe, and the apex of which is at a, and thus an imprefiion fufficiently forcible to produce diftinct vifion is made on the retina. In the preceding inftance, the" luminous body A ••vas confidered as a point, and what has been faid of it will apply to every point of a vifible object, which is capable of tranfmittiug or reflecting to the eye a pen- cil or collection of rays. Thus we may eafily fup- pofe that from every point of the arrow A, D, B, (Fig. 7.) pencils of light may be tranfmitted ; thefe, like all pencils or collections of rays, coming from a j$oint, will diverge, and will fall upon the eye in the form of cones or pyramids, fuch as A, M, C, from the, point A ; D, B ay B by B r, B dy B e, C a, C by C cy C dy and C e can come. But though rays are reflected from every point of the object to every point of the circum- ambient fpace, yet it is evident, that only thofe rays which pafs through the pupil of the eye can affect the * fenfe; 398 Objeffs Jeen Jingle ly two Eyes. [Book IX. fenfe j thefe rays give aljfo the idea of different colours, according to the properties of the bodies which tranf- iriit or reflect them, upon the principles formerly de- monft rated. It is very difficult to explain how it happens that two diftinct images are painted upon both eyes, and yet that we only perceive a fingle object. This dif- ficulty has been attempted to be foived by having recourfe to the power of habit ; but I confefs I can- not help being of opinion with Dr. Reid, that the correfpondence of the centers of the two eyes, on which fingle vifion depends, does not arife from cuftom, but from fome natural ccnftitution of the optic nerves. The cafe of the young man born blind, who was couched by Mr. Chefelden, and who faw fingly with both eyes, immediately upon receiving his fight, is ve*y properly adduced by that refpectable author in favour of this fuppofition. He alfo found, that three young gentlemen, whom he endeavoured to cure of fquinting, faw objects fingly, as fqon as they were brought to direct the centers of both eyes to the fame object, though they had never been ufed to do fo from their infancy ; he remarks too, that there are cafes in which the fulled conviction of an object being Tingle will never make the object appear fo, even by the longeft practice, as in the cafr of looking through a multiplying glafs *. In thofe who fquint, the diflance between the two pupils is confiderably lefs than in other perfons, for when the pupil of the undiftorted eye is feated in the middle of the orbit, as in looking diredly forwards, the pupil of the other eye is drawn clofe to the nofe, fo that the two axes are never pointed at the fame ob- * Reid's Inquiry into Human Mind, p. 267. Chap. 41.] Caufe of Squinting. 399 ject, though the mufcles fo far act in concert with eacfr other, as to move both eyes the fame way at the fame inftant of time. Dr. Jurin obferves, that this vicious habit may eafily be contracted by a child, if he is laid in his cradle in fuch a pofition as to perceive the light with one eye only. The moft common caufe of fquinting is, however, an inferiority in the fight of one of the eyes. Dr. Reid aflferts, that having examined above twenty per- fons, who fquinted, he found in all of them a defect in the fight of one eye. Four of them only had fo much of diftinct vifion in the weak eye as to be able to read with it, while the other was covered j the reft faw nothing diftinctJy with the defective eye *. When the eyes are equally good, we fee witfv both eyes more diftinctly than with one, by about a thirteenth part ; but when the eyes are unequal in their powers, objects appear lefs diftinct with both eyes than with one. It is no wonder, therefore, that fuch perfons mould chufe to make ufe of one eye only, and to turn the other afide ; the weak eye, in this cafe, is generally turned to the nofe, becaufe in that fituation the direction of its axis is as diftant as poffible from that of the good eye j and befides. this, the nofe cot>- ceals many objects from its view. This is, however, not the only caufe of fquinting ; it is fometimes, though rarely, the effect of habit, as was intimated refpecting children being laid in the cradle with one eye turned from the light, or covered. When the eye that fquints is turned outwards towards the temples, that cad of the eye is commpnlv the mere effect of habit. If the eyes differ much in point of goodnefs, the cure will be extremely difficult. When they do not j* Reid';. Inquiry into Human Mind, p. 2^3. materially 4co Power of Sight limited. [Book IX, materially differ in this refpedt, the proper and natural cure is to cover the good eye for fome time j for in this cafe the diftorted eye is obliged to act, and to turn itfelf directly to objects, which in a little time becomes natural and eafy to it. Even a very weak eye acquires ftrength by exercife ; peffbns whofe fquint- ing feemed almoft incurable, having covered their good eye for a few minutes only, have been themfelves furprifed to find the ftrength that their bad eye had acquired by exercife even for that fhort period. When the fquint has proceeded entirely from a vicious habit, a cure has been effected by covering the good eye for a fortnight only *. The power? of this fenfe are limited, as well as thofc of every other fenfe and faculty of man. i ft. The fight is very limited with refpect to bodies in motion ; for with a certain degree of velocity, as that of a cannon ball through the air, they are not vifi- ble, unlefs very luminous. 2. The fame effect is exemplified by the experi- ment of whirling a .lighted coal, as was already in- timated. 3. If two objects unequally diftant more with the iS,me degree of velocity, the more remote will appear the flower. 4th. A vifible object moving with any velocity appears to be at reft, if thf fpace defcribcd in a fecond of time is invifible to the eye. Thus a near object, as the index of a clock, moving flowly, or a remote one, as a planet, moving fwiftly, appears to be at reft. 5th. It is well known, that when the eye is proceeding ftrait forward, as in a boat at fea, a lateral object, either at reft, or moving not fo faft, ap- pears to move the contrary way. 6th. If, however/ * Reid's Inquiry 5nTo the Human Mind, p. 253. thtf Chap. 41.] How tbe ~Eye judges ofDiftanct. 401 the object is at a very great diftance, it will feem to go the fame way, as when a perfon runs by moon- light, the moon appears to accompany him. 7th. If two or more objects move with the fame velocity, and a third remains at reft, it will appear in motion while the moving ones feem at reft ; this is exemplified by the moon and the clouds. There are fix natural methods, by which we judge of the diftance of objects from the eye. ift. By the angle which is made by the optic axes. For want of this direction it has been obferved, that perfons who are blind of one eye frequently mifs their mark in pouring liquor into a glafs, &c. 2.ndly, and I think moft generally, by the apparent magnitude of ob- jects. By depending upon this method we are very frequently deceived in our cftimates of diftance by -any extraoidinary large objects, as in travelling to a great city, church, or caftle, we fancy them nearer than they really are. This furnifhes. us with a rea- fon why animals and other fmall objects fcen conti- guous to large mountains appear exceedingly fmall j for we imagine the mountain to be nearer to us thaa it actually is. When we look down alfo from a high building, the objects beneath us appear much fmaller than they would at the fame diftance on the level ground j the reafon is plainly, becaufe we 'have no diftinct idea of diftance in that direction, and therefore judge by the impreffions upon the retina, whereas cuftom has corrected our judgment in the other cafe. The third method of determin- ing the diftance of objects is by the force and vivid - nefs of the colours, and the fifth is analogous to it, namely, by the different appearance of the minute parts. When thefe appear diftinct, we judge the ob- ject to be near, and the contrary when they appear VOL. III. Dd faint 402 Why the Banks of a River feem contiguous. [Book IX. faint or confufed. 6thly, We are affifted in judging of the diftance of any particular objects, by the other objects which are interpofed. On this account, dif- tances upon uneven ground do not appear fo great as upon a plain ; for the valleys, rivers, and other objects that lie low, are many of them loft to the fight. This too is the rcafon why the banks of a river appear contiguous when the river lies low and is not feen *. In children the pupil is ufually more dilated than in grown perfons. The rea-fon of this appears to be, that in childhood the cornea is more flexible, fo as to be very eafily bent into any curvature necefiary for diftinct vifion, and confequently the pupil has lefs occafion to contract. In grown perfons the cornea is {lifter, they have therefore more neceflity to contract the pupil. In elderly perfons the cornea grows ftill more rigid ; for this reafon they are obliged fometimes to hold the candle between the eye and the paper on which they read ; and their doing fo is a direct indi- cation that they begin to want fpectacles f. Children read much nearer than grown perfons, both becaufe their eyes are fmaller, and becaufe their cornea is more flexible. That elderly perfons fee better at a great diftance than younger perfons is gene- rally allowed. It is a certain and very important fact, that long- fightednefs may be acquired, for countrymen, failors, and thofe that are habituated to look at remote ob- jects, are generally long-fighted, want fpectacles fooneft, and ufe the deepeft magnifiers ; on the other hand, the far greater part of the ihort fighted are to * EfTay on Vifion, quoted by Prieftley. f Porterfield on tl.e Eye, quoted by JPneit. Op. Per. 6. f. 12. be C hap. 41.] Cautions for the Prefervation cf Sight. 40 j be found among ftudents, and thofe who are con- verfant with fmall and near objects ; every one becom- ing expert in that kind of vifi6n which is moft ufeful to him in his particular profeffion and manner of life. Mr. Adams, in his very ufeful efiay on vifion, has given fome rules for the prefervation of the fight> which, for the -benefit of the Itudious reader, I have thought it proper to infert. i ft. Never fit for any length of time in abfolute gloom, or expoied to a blaze of light. From this rule may be deduced the impropriety of going haft ily from one extreme to the other, whether of darknefs or of light, and it may be inferred that a fouthern. afpect is improper for thofe whofe fight is weak and tender* adly. Avoid reading a fmall print. 3dly. Do,not read in the dufk, nor, if the eyes are difordered^ by candle light. 4thly. The eye mould not be per- mitted to dwell on glaring objects, more particularly on the firft waking in the morning 5thly. Th'e long fighted mould accuftom themfelves to read with rather lefs light, and fomewhat nearer to the eye than ufual, while thofe who are fhort fighted mould ufe themfelves to read with the book as far off as poliible* Dd a I 404 ] [Book IX. CHAP. XLII. THE GESTATION AND BIRTH OF ANIMALS* Varieties in the Production of Animals. — Proportion of Males to Fe- malts. — Growth of the Foetus.— Oviparous jfnimals. — Mode of Exi/icnce before Birth. — Weight of a new born Infant.—Mifcella- neous Calculations concerning (he Proportion of Births to that of Deaths in Infancy, &c . WE have hitherto been occupied in confi- dering the functions which relate to the exift- cnce and welfare of animals, let us now direct our attention to thofe which, nmidft the decay of indivi- duals, prefer ve the continuance of the fpecies. Among the more minute, and imperfect animals, there are fome which may be multiplied from frag- ments of the fame fpecies, as the polypus j others grow from the bodies of their parents, and are in due feafon fet at liberty to feek nourifhment for them- felves j fome animals, at a certain period of their exiftence, naturally divide into feveral parts, each of which afterwards becomes a perfect animal of the fame race. As we afcend in the fcale of animal exiftence, a difference of fex prefents itfelf as a leading distinction. We find fome races of animals, of which every in- dividual is pofTefled of both male and female organs; others, among which a fingle female breeds for a whole community, and among which there are very few individuals pofTefTed of fexual organs. In general, however, about half xthe individuals of a fpecies are males and half females. It Chap. 42.] Theories of Bttffon and SpalanzanL 40$ It is in ibme meafure foreign to the objects of the prefent work to enter on thofe theories with which phi- lofophers have amufed themfelves and their readers concerning the generation of animals. Independent of the indelicacy of the fubject, there is another ftrong ob- jection to their introduction here ; fince thefe theories reft upon no other foundation than conjecture, and fome fallacious, and, I think, delufive microfcopical obfervations. I mall, therefore, content myfelf with referring the reader to the natural hiftory of the Count de Buffbn, and for a direct contradiction of his theory to the Abbe Spalanzani. The former of thefe philo- fophers has derived the principle of animal exiftence from the male, and the latter from the female. The generation of fifties appears, indeed, greatly to favour the theory of Spalanzani, for in that inftance at leaft, the rudiments of the young animals appear to be con- tained in the eggs or roe, which the female fifh firft depofits j and the milt which is afterwards depofited by the male appears only to excite them into action and growth. If we admit thus much of his theory, however, we muft attend him a ftep further, and fup- pofe that every female ovum in the ovarium of a female muft itfelf contain ovaria and ova, and by extending the fame idea we muft be led to conclude, that the rudiments of all the animals, which have exifted, do exift, or ever will exift, were originally contained in the ovarium ofithe firft female of the particular fpecies to which they refpectively belong. This has been therefore called the theory of involution, and has been fuppofed equally applicable to animals and vegeta- bles. In the procefs of generation, the firft marks we fee, after impregnation, of the future progeny, is a minute being without limb or feature, connected by a cord to D d 3 th<- 406 Growth of the Toung in the Egg. [Book IX, the internal furface of the uterus, and furrounded by very thin membranes. It feems formed, however, of two mafles joined together, the larger of which is the head and the fmaller the body. As the foetus' advances in growth the body acquires a larger fize with refpect to the head, fmall protuberances make their appearance on the body, which are the future limbs, and the fea- tures begin to manifeft themfelves; In this manner the foetus, gradually acquiring a more determinate ftru£bure, and more evident marks of the fpecies to which it belongs, is at length difengaged from the mother. In different fpecies there is great variety in the perfection of the animal at the time of birth ; the young of the human fpecies is, perhaps, the mod back- ward of any in this refpecl: -, for' a- child, when fix months old, is not fo able to provide for itfelf as a horfe or an afs at the age of as many days. In many races of animals it Ihould be obferved, particularly in birds, the growth of the fcetus takes , place out of the body of the mother. This is indeed the cafe with all animals which fpring from eggs, and in which we have a very favourable opportunity of ob- ferving the progrefs of the fcetus from its firft appear- ance till it has acquired that ftate of perfection at which it is hatched. During the whole period of its growth it is fupported by a limited quantity of nourifhmenc contained within the egg- (hell, and which is that part of the egg called the yolk. The human fcetus is furrounded with three mem- branes; the external of thefe is vafcular, and is called the fpongy chorion ; the middle coat, called the media or true chorion, and the internal one, called the ana- pion, are not fo. Mr. Hunter has found the fpongy chorion to confift of two, layers j that which lines the uterus he calls membrana caduca or dssidua^ becaufe it Chap. 42.] Situation oftheFcrtus, 6?r. 407 is caft off after delivery j _ the portion which covers the ovum, decidua reflexa, becaufe it is reflected from the uterus upon the ovum. The membrana decidua is, according to Mr. Hunter, perforated with three foramina, viz, two fmall foramina, correfponding to the openings of the Fallopian tubes at the fundus uteri, and a larger one oppofite its cervix. The decidua reflexa becomes more thick and vafcular as it ap- proaches the placenta, and conftitutes its maternal part. The foetus appears floating in a tranfparent fluid contained in the amhion, fufpended by the umbilical cord, and the head, being the largeft part, and the in- fertion of the umbilical cord being at a confiderable diltance fron\ it, falls loweftj a circumftance very ne- cefTary to fafe &nd eafy delivery. The foetus, when it has nearly obtained its growth, is curled up in an oval form j its back is round, and turned towards one fide of the mother, making that fide more protuberant; its chin is prerTed againft its bread; with its arms it em- braces its knees, and its heels are clofe to its buttocks. A mod curious but fomewhat complicated branch of the animal oeconomy, is the means which nature em- ploys for carrying on the nourifhment of the foetus. I have already mentioned the umbilical cord, which con- nects the foetus to the uterus. One end of this cord is connected to the fubftance called the placenta, and the other enters the navel of the fcetus. The placenta is a fpongy fubftance as broad as the crown of a hat, and about two fingers in thicknefs, and is commonly attached to the upper part of the uterus. The outer furface of the placenta is foft, tender, and fpongy, and commonly bloody, on account of its feparation from the y.efiels of the uterus. Its internal furface, where it is covered by the membranes, is firm, glofly, and D d 4 beautifully Situation and Growth [Book IX* beautifully marked with the ramifications of blood- vefiels. On the qucfide the blood -veffels can fcarcely be obferved, as they are there very minute. On the outfide of the placenta there is alfo an ap- pearance like a divifion into lobes. The umbilical cord is generally inferted, not into the middle, but to- wards the edge of the placenta, which facilitates its reparation after delivery. With the placenta, as has been fuppofed, the arteries of the uterus have a com- munication, by which, in the firft periods of geftation, the foetus receives a ferous fluid, and in the later pe- riods a large quantity of blood. It has alfo been taken for granted, that the arteries of the umbilical cord communicate with the veins of the uterus, and that thus a circulation of fluids is maintained between the fcetus and the mother. Mr. Hunter, however, after numerous experiments, has adopted a different opinion. By a variety of trials by injection he finds, that fluids thrown into the veflels of the umbilical cord never get into thofe of the uterus ; and on the contrary, thole thrown into the veliels of the uterus find no admifiion into thofe of the umbilical cord ; he therefore concludes, that the human placenta, as well as that of quadrupeds, is a compofition of two parts inti- mately blended, viz. an umbilical or infantile portion, and an uterine portion. The former by maceration, is found to confift of the ramifications of the veflels of the umbilical cord, the other Mr. Hunter confidered as an efflorefcence of the internal furface of the uterus, •which forms a membrane, fending numerous procefies into the fubftance of the placenta ; this latter is the membrana decidua, Mr. Hunter does not pretend to fpecify the nature of the union between thefe two por- tions of the placenta. Th* Chap. 42.] in tht Fat us. 40 9 The veins of the placenta unite into a Tingle trunk, which, leaving the placenta, enters the navel of the foetus. Two arteries, which are continued from the internal iliac arteries, pafs out at the navel of the foetus and enter the placenta; and thefe, with the vein above mentioned, conftitute the umbilical cord. By means of thefe arteries and veins, a communication is maintained between the fcetus and the placenta. The umbilical veflels do not run in a direct courfe, but both the arteries and the vein are mutually twifted about each other. The umbilical cord paries from the fcetus to the placenta, through the liquor amniL The winding courfe of thefe veflels, and the elafticity of the fubftance which furrounds them, protect them in a great meafure from the bad effects which would otherwife happen, from their being ftretched or piefTed, which might put a flop to the circulation. Befides thefe vefTels, however, there is another ia brutes, called the urachus, which conveys the urine from the bladder to a vefifel called the allantoides. In the human fpecies, both the urachus and the allan- toides are wanting. There is, indeed, in the human fcetus, fomething like an urachus, which goes from the bladder of the foetus to the navel, between the umbilical arteries, but it feems to be of no ufe, as it does not communicate with the bladder. The umbilical vein, after it has entered the body of the foetus, divides into two branches, one of which enters the vena portarum to be diftributed in the liver; the other, which is called the ductus venofus, carries its contents to the left vena cava hepatis, which ter- minates in the great vena cava ; and that part of the blood -which paries through the liver alfo arrives at the vena cava. From the vena cava the blood pafTes into the anterior 410 Circulation cf the Blocd in the Fcetus. [Book IX. anterior auricle, whence there is a paffage into the pofterior auricle, -which is clofed up after birth, but \vhjdi now turns the'greater part of the blood received by the anterior auricle, from the anterior to the pofte- rior cavities of the heart. A confiderable quantity of blood, however, notwithftanding this palfage, does pafs into the anterior ventricle j but all the blood which is received by the anterior ventricle is not fent K> the kings, which before birth are too much con- dcnfed to tranfmit fo large a quantity ; part of it is" turned afide by a veflel called the ductus arteriofus, which paries from the pulmonary artery to the aorta. Tims, befides the blood which efcapes paffing through the lungs by means of the pafiage from the anterior to the pofterior auricle, a fecond portion efcapes by the velTel which leads from the pulmonary artery to the aorta, fo that perhaps not more than a fixth part of the blood which paffes through the reft of the body paffts through the lungs before birth, whereas, after thefe paffages are clofed, every drop which is circulated in the body muft neceffarily circulate alfo through the lungs. Thefe pafiages, which are peculiar to the foetus, from caufes not afcertained clofe up very quickly after birth. The blood is returned from the fcetus by the arterias umbilicales which are the in- ternal iliac arteries of the adult, but which in ' the fcetus pafs out at the navel, and are continued to the placenta, The fcetus, which in the early periods of gefta- tion was almoft all head, is ftill at the time of birth of very different proportions from thofe of the adult body ; the head is remarkably large, and the lower extremities remarkably fmall. The growth iif the fcetus in the uterus is by no means uniform. The weight of childrena when born at' the full time, varies from Chap. 42.] Calculations resetting Births } &c. 41 j from fomething more than four pounds to a little more than eleven. By far the greater number weigh from five to eight pounds, avoirdupois. At the end of the third month, the bulk of the foetus, with the membranes and placenta, is very inconfiderable, as is feen in abortions, which are moft frequent at this pe- riod of geihtion. During the courfc of the fourth month the uterus becomes too large to remain within the pelvis, and rifing into the abdomen, gives lome flight degree of protuberance. The foetus now in-- creafes much fafter than before ; but the principal part of its growth is performed during the three laft months of geftation, when the uterus at length rifes as high as the ftomach, preflmg the inteftines towards the backbone. The diftended uterus is now ftimu- lated to contraction, and the pains of child-birth arc fucceeded by the effufions of maternal fondnefs. It appears from a very accurate regifter, kept by Dr. Clark, phyfician to the Lying- inn Hofpital at Dublin, that the proportion of children is about nine males to eight females j — children dying under fixteen days old, as one to about fix and an half; — children ftill-born, as ons to twenty; — women having twins, as one tv fixty $ — women dying in child-bed, as one" to about eighty -fe-ven. There is, however, a greater mortality of male children, owing, as Dr. Clark fuppofes, to their greater fize, and particularly to the fize of the head, which becomes injured in parturition, and confequentty affects the health; and the proportion is reduced to quite equal before the age of puberty. If every mother in a great city was obliged to fuckle her own child, the proportion would be one good nurfe in Jive j and in the country, not one bad nurfe in ten *. * Clark's Observations, Phil. Tr. 76. [ 412 ] [Book IX. CHAP. XLIII. THE GROWTH AND DECLINE OF THE BODY. Increafe of the Bo dy btforg and aftzr Birth. — Difproportitn nf the Parts dscreafes 'with Growth, — What Parts firft ceafe to increafe in Size. — Youth. — Manhood. — Fir/} Symptoms nf Decline. — 'At what Period old dge generally commences. — Symptoms of Age.—Caufts nuhy the Human Frame cannot be of long Duration. FROM the time of conception till birth, the growth of the body proceeds in an accelerated or in- creafing proportion, that is, the growth in the fixth month, for inftance, is greater in proportion than in the fifth ; from birth tili manhood it is gradually lefs and lefs, in other words, the growth of the fecond year is lefs in proportion than that of the preceding, and fo of all the fticcceding years. The reafon commonly affigned for the latter of thefe facts is, that the fibre becoming lefs diftenfible from an increafe of folidity as we advance in age, our growth is confequently lefs rapid. But if the rapidity of growth was proportioned to the laxity of fibre, the foetus ought to increafe mcft rapidly immediately after conception, and more (lowly as its texture becomes more firm. The contrary of this, however, is found to be the fact, fmce, in the early periods of geftation the increafe of the foetus ib very (low, and its growth is continually accelerated till the birth. From this fbtement it muft be concluded, that laxity of fibre is only one among other caufes which favour the increafe of the body. As the body advances in growth, its difprcportions are gradually loft; the head increafes more Chap. 43-1 Symptoms of old Age. 413 more flowly, and the lower extremities with more ra- pidity. The head indeed ceafes to grow much fooner than the other parts ; for thefe, and particularly the thorax, feem to gain fize and ftrength for feveral years after the head, has arrived at its utmoil dimen- fions. At the age of fifteen or fixteen years, fooner in fe- males than in males, and fooner in warm countries than cold, the figns of puberty begin to manifeft themfelves, and feveral changes now take place in the body, which it would be improper to (late. When the body has attained its full growth and ftrength, it does not immediately decline, but remains in a ftate of nearly equal vigour till between forty and fifty years of age. At this time the body begins fenfi- bly to lofe its agility, and the approaches towards old ay;e, which had hitherto been infenfibly going on, now begin to manifeft themfelves. But though the "body has now loft confiderably of i;s agility, yet in perfons of good conftitutions, and who have not been remarkably intemperafie, its ftrength re- mains pretty entire. After the age of fifty, however, the decline of body becomes much more apparent; there is no longer that fpring and vigour of motion; and labour becomes more irkfome and painful. From the age of fixry to that of feventy the health is fre- quently pretty good, but the ftrength fails confiderably. Threefcore and ten years is the age of man ; and though there may be forae remarkable inftances to the con- Jrary, yet, in general, exiftence protraded beyond this period is forrow and mifery. In the whole progrefs of life the body is continually becoming lefs vafcular. The vivid bloom of youth, which is owing to the ramifications of minute arteries in the (kin of the cheeks, fubfides into the moderate hue 414 Growtk and -Decline of tie "Body. [Book IX* hue of middle life, and this into the wrinkled and ihrunk appearance of old age. Similar changes are taking place in other parts of the body, and the coats of the arteries gradually becoming thicker and ftronger •with refpecl to thofe of the veins ; thefe latter become more diftended, and the livid hue of venous plethora fucceeds to the vivid tint of the arterious. A difpo- fition to folidity invades the body in the progrefs of life, and that which in the child was pliant cartilage^ becomes in the old man brittle bone. The quantity of earth in the compofition of the dif- ferent parts of the body is continually increafing ; the mufcles become infenfible to the ufual ftimuli j the vi- gour of the circulation is diminimed; and in the few, the very few, who efcape the numerous pitfalls of dif- eafe and accident, this rigidity and infenfibility increaf- ing, neceflari-ly puts an end to exiftence. That modern difcoveries, or the improvement of the medical art, mould be able to protract for any confiderable period our mortal exiftence, is a notion that will only be entertained by thofe who are ignorant of the phyfiology of the animal frame, and indeed of every other branch of fcience. It is the natural confe- quence of extenfive knowledge to abate our confidence ; •while impudence, dogmatifm, and vain and vifionary peculation, are the genuine offspring of ignorance. Medical ikill may indeed be fuccefsfully applied in oc- cafionally arrefting the progrefs of thole difeafes, which might otherwife prematurely interrupt our mortal ca- reer j yet even in thefe inflances, thofe who have ftudied moft, and practifed moft, will be the moft fen- fible of the impotence of human knowledge in this important art j but he who is at all acquainted with the delicate and fragile texture of the human -frame muft Chap. 43.] Old Age and Deatb. 415 muft be abundantly fcnfible, that it is a fabric which was not meant to endure for ever. In the gradual decline of life, to which all muft fub- mit, let us earneftly embrace that confolation which re- ligion affords us. Thajt which fweetened the cup of - « death to Socrates is through life the cordial of the chrif- tian ; it is a confideration that will moderate prof- perity, and will deprive adverfity of its mod poignant forrows j it will cheer us in life, and at the hour of death it is the only circumftance that can impart a ray of comfort to the human foul. [ 4*6 ] [BookX. BOOK X. GF THE HUMAN MIND. CHAP. I. OF THE STUDY OF THE HtJMAN MIND. Our Knowledge of Mind limited. — Confufed by Metapby/ics. — Plan nf this Inquiry — The Fir/I Part refpe£s the Injlruments and Modes of A3ion of the Human Mind. — The Second, the Springs or afti*ve Powers. — The Third, the mo/l important Qucjticm in Moral:, &c. " TT/r NOW thyfelf," is a faying of great antiquity j JA, and an author, whofe fentiments are defervedly converted into maxims, has aflerted, that " the proper " ftudy of mankind is man." It is, however, a cir- cumftance ftifficient to mortify the pride of reafon, that even on the fubjeft moft interefting to us, we muft be content with a limited portion of knowledge ; we muft not extend our expectations too far. Even with reipecl: to our own minds, there are forne points which appear to be removed beyond the reach of our re- iearches, while others are, perhaps unnecefTarily, in- volved in doubt and difputation. It is unfortunate, indeed, that in no branch of fcience whatever the ima- gination has more wantonly fported than in this ; in no fcience Tiave men appeared fo defirous of deferting the only fure guide, experience -, in no inftance has ir beeji Chap, i.] Danger and Abjurdlty of Metaphyfics. 417 been thought proper to refort fo little to proof and obfervation, or to attribute fo much to conjecture and theory. Metaphyfical fubtleties, and hypothefes carried to a vifionary extreme, have, therefore, greatly contri- buted to confufe this branch of knowledge ; though when extricated from thefe, I apprehend full as much is known in this fcience as in any other, and perhaps more than in moft. On this account I fhall carefully avoid all thofe difputed points concerning identity and diverfity, exiftence, infinity, &c. that haye divided the learned from time to time. I confider them, in truth, as utterly foreign to my purpofe, and as tending to eftablifh no one uieful principle. It will be unneceflary alfo to examine the origin of our ideas, or to enter into nice difquifitions concerning fpace, duration, &c. &c. as fuch inquiries are certainly more curious than ufeful. I (hall further avoid all fanciful theories refpecting the nature of our perceptions. Some of them, 1 confefs, are plaufible, but J rather chufe to lay the ground work of my reafoning on actual experience j let thofe who fo incline, extend at their leiiure their refearches further. That fcheme, which reduces the moral powers of mart to the fewelt principles, if thefe can be demonftrated ade- quate to_every effect, is moft fatisfictory to the rational inquirer. The more of nature we difcover, the more fimple (he appears in her operations : it is unphilofo- phical unneceffarily to multiply caufes. It is evident, for inftance, that there exifts in men a relifh for beauty, as well as for moral excellence, and an antipathy to vice and deformity. But how are thefe affections ge- nerated ? It is an indolent method of philofophizing to ftop at whatever is noc eafily underftood. Final caufes VOL, III. E e ancl 41 8 Materials of [Book X. and inherent inftinft have faved the labour of many a painful inveftigation. With refpeft to the aclual exiftence of innate ideas or principles, the reader will perceive that I am not anxious to renew the controverfy. Innate ideas, I be- lieve, have been in general given up by philofophers fince the time of Mr. Locke. A moral principle has, indeed, been contended for by fome writers of the 'higheft reputation, as being innate in man. It may be coniidered either as a fixth fenfe, as fomething infe- parable from the foul or mind of man, or as a general inftinftive refult of his mental organization. I muft obferve, however, that the exiftence of fuch a principle- has never yet been fatisfaclorily proved, though on the contrary it is not eafy to difprove it ; I fhall, therefore, as much as poffible, avoid the controverfy, and endea- vour, as far as obfervation enables us, to account for the operations of our minds in the fimpleft and eafieft manner, and to have as little recourfe as poflible to prin- ciples which are involved in doubt or obfcurity. The elementary part of this book will naturally di- vide into two branches. The firft part will extend to the end of the eighth chapter, in which I mall endea- vour to explain the inftrumenEs and the modes of a<5Hon of the human mind. The fecond will extend from the ninth chapter to the thirteenth, in which the fprings or incentives that produce action in the mind, and in- fluence its movements, will be examined. The materials, upon which the human mind is prin- cipally to ad, are die traces or veftiges left by external impreflions on the five fenfes. Of thefe a fimple effecl: on any one fcnfe produces what is Cdikdajft^frrtfttfj the word idea fignifying an image or reprefentation in the mind of an action, quality, or fenfation ; thus white fimple ideas. AB Chap, i.] Wiongte. 419 An idea, compounded of feveral fimple ideas, is called a complex idea, as man, horfe, tree, &c. which are evi- dently compounds of a number of fimple ideas of figure, colour, folidity, &c. and fometimes for diftinc- tion's fake, when many complex ideas are compounded in one, the dilciples of Mr. Locke call it a decomplex idea, as homicide. Impreffions on the fenfes are often fo entwined or aflociared together, that the idea of the one fhall not be recollected without that of the other. This junc- tion happens when two impre (lions are made on the fenfes at the fame time : thus the wb'itenefs and rouvd- •nejs of a globe may be afibciated ; the form and the found of a mufical inftrument ; the name with the thing, fo that on the fight of the thing or object we immediately recollect the name. Ideas may affociate with impreflions, if an imprefllon is "made on any of the fenfes, while an idea is predominant in the mind. Thus the fight of a particular place will often recal fome interefting train of thought, that may have been entertained there. When I fpeak of ideas being aflb- ciated, connected, combined, &c. I would be under- itood of the fame thing, viz. the implexion or junction of ideas thus explained. The retention of ideas in the mind is called memory. The act of combining old ideas into new ones, inven-' lion, and frequently imagination or fancy. The act of examining and comparing them judgment Under thefe heads I propofe explaining the primary operations of the mind, and thefe will constitute the firft part of the prefent inquiry. The fecond part of this book will confift of an in- quiry into the common fprings of action in the mind. Thefe I fhall endeavour to prove to be ultimately the fenfes Qtplsajurc and pain. Low is the idea of pieafure, £ e 2 combined 4^0 Plan of Inquiry. [Book X. combined with fome other idea; hatred 'the idea of pain, combined in the fame manner. Defire and averfion aje active love and hatred *. The third part, which extends from the thirteenth chapterto the conclufion of the work, will confift of the application of thefe principles to the inveftigation of fome curious fubjefts, and to the theory of morals. This, as it is the moft extenfive part of the fubjecl, is neceffarily the moft imperfect, and the chapters that conftitute this part, are rather exhibited as confirmations of the preceding principles, than as a complete fyftem. / * The natural appstites of man arr, I. The common call of nourijbment for the body. zd. The de- fire of propagating the fpecies. The natural pleafures of man are, ift. The fatisfyingof thefe appetites. 2d. The general plea - fure refulting from the moderate and proper exercife of the organs 6r faculties. Chap. 2.] [ 421 ] CHAP. II. OF PERCEPTION. tf'hc Senjes the great Source of Information.— T)iftin£licn letnueen Sen- Jilt ion and Perception.— Senfes correct each piker.— Whether the fame Qbje&s produce fimilar Perception: in different Men. — Id:as. THAT the mind is obliged to the fenfes for the great mafs of its information, is now an efta- blimed principle. The proofs of this doctrine I mall decline entering upon for reafons already afligned. I would only cbferve, Firft, That I do not fee why we are furnimed with fenfes by the author of nature, if not, for this purpofe. Secondly, The fenfes feem entirely adequate to all the information we are pofiefied of. Thirdly, Perfons wanting any of the fenfes appear en- tirely deftitute of the ideas of that fenfe. A gentle- man, blind from infancy, affured me, he never re? membered to have experienced in a dream any thing like what the fenfe of feeing is defcribed to be. NaVj thofe who have all the fenfes complete, derive plainly their knowledge from the exercife of them. A child does not fhriflk from a candle till it has felt the pain- ful fenfaticn of burning, or is warned againft it in terms exprcffing pain, of which it forms a judgment from pain already experienced. A very proper diftinction is made by Dr. Stuart, between fenfation and perception. Senfation implies t. i. c. 3. I do not in faft find that any one difcovery has been made in the Science of mind fmce the time of Hobbes, Two 430 Synchronous Aff'octatlcn. [Book &, Twofenfations happening at the fame time will be- come united, and the ideas will be united of courfe ; thus the ideas of the figure and colour of bodies, ad- mitted by the eye, are united, and thefe may be united with another idea admitted by the touch. As the ideas of roundnefs and whitenefs by the former, and folidity by the latter, are aflbciated together in the complex idea of a (lone. If mufic is heard, while we behold the inftrument, the found will be aflbciated with the vifible appearance, and the former will at any time recal the idea of the latter, when we do not fee the in- ftrument*. Names become afibciated with things, and things with actions f. AiTociations formed from impreffions made at the fame time, are called fynchro- * " The names, fmells, taftes, and tangible qualities of na~ tural bodies, fuggeft their vifible appearances to the fancy , and vice verfa." — Hartley on Man, c. i. f. i. prop. 5. f " It is remarkable, how-ever, as being agreeable to the fupe- rior vividuefs of vijible and audible ideas, that the iuggeftion of the. vifible appearance frqm the name, is tic inoft ready of any."— Ibid. ' TRe tranfition from the words to the ideas, is generally much eafier than from the ideas to the words. A perfon who is learning a ftrange language, will be able to underftarsd a book in that language long before he can write cr fpeak It. Even in one's native tongue, one cas readily underftand what is written or fpokeH in the beil and propereft terms, though he cocH not have ufed thefe terms for exprefiing the fame kleas. This proceeds from the influence of cuftom, &c. The ideas are more familiat to us than the words : they are often raifsd by their proper objefts, or fuggefted by other words : and their familiar ify makes them be; fuggelted readily. That this is the true caufe, is confirmed by obferving that where it does not take place, ideas are not fug-- gefted more readily than words are in ordinary cafes. When the ideas expreffed are fuch as we have been little accuilomed to at- tend to, a difcourfe or competition is underftood by us with diffi- culty, as well as when ideas are expref&d by uxafual words,'— Qevard on Gen. pt. 2. f. 2. note. nous Chap. 4.] Succsflfoc Affociatwn. 43 t nous. But it is evident that impreffions remain fome moments on our fenfes, and die gradually away * ; if another impreffion therefore is made while the former remains, they will be aiTcx iated, and the one (hall recal the other to remembrance ; the alTocintion being weaker or ftronger in proportion to the ftate of tha idea or impreffion with refpect to its vividnefs. An idea may in the fame manner be aflbciated with an irn- preffion or fenfation, or two ideas may be afibciated together, and this kind of affectation from contiguity of time may be termed fucceffive. Thofe com- plex ideas which are formed from fynchrorious impref- fions, are more vivid and diftinct than thofe formed from fucceffive ones. Propofitions founded upon fynchronous knpreffions, are little elfe than complex ideas of fenfation ; as in the propofition " the dog barks," the idea of die thing is as much aflbciated .with the action as with any of its qualities : and here is no room for difienr, Unleli we could find that our fenfes had deceived us. Propofitions founded on fucceffive imprefiions, are much more liable to error} yet of thefe confiftsby far the more valuable portion of our knowledge. !{: is remarkable, how in forming thefe proportions, .fre- quent experience leads us to drop the intermediate ideas, and connect the two extremes of the propofition, calling it felf-evident, as if it was really the effect of fynchronous impreffions. <£ We may obferve (fay* Mr. Locke f.) that the ideas we receive from fenfa- tion, areoften in grown people altered by the judgment without our taking notice of it. Thus a globe of any uniform colour, as of gold or jet, being fet before our eyes, the idea thereby imprinted, is of a flat circle va*- * See Sir Ifaac Newton's Optics, and b, ix, c. 41. t P.. 2, c. g. rioufly 432 Sticcejjrve Affectation. [Book X, -rioufly ihadowed. But being accuftomed to perceive what kind of appearances convex bodies are wont to make in us j the judgment alters the appearances into their caufes ; and from that variety of Ihadbw or colour, frames to itfelf the perception of a convex figure of one Uniform colour." A man who reads or hears with attention, takes little notice of the characters or founds, but of the ideas that are excited in him by them. Thus we find the intermediate, affociating ideas are dropped, and the more remote caufes immediately con- nected with the -effects. In the inftance of the globe, the firft complex idea prefented, is that of a circle aflpciated with certain fhades of colour ; on approach- ing and examining it by the touch, we find that this is really a convex figure and of a felf-colour, we there- fore aflbciate the ideas of the convexity and colour with the former idea of the circle fo lhadowed, and the one occurs not alone, but always accompanied with the other, and fo immediately, that we feel it as if it ,had been from fynchronous impreflions. The affo- ciat'ion foon becomes fo flrong that we are liable to be . deceived by it, for when we fee objects well painted on canvas we can fcarcely conceive that they are reprefeated by different fhades on a flat furface, and a child very naturally employs his feeling in order to fatisfy himfelf. It is unneceffary to multiply instances ; it is obvious that the fight of blood never fails to alarm the mind inftantaneoufly, though no more productive f>f fear or horror from its natural properties than any other fluid. " Painters, ftatnaries, anatomifts, archi- tects, fee at once what is intended by a draught, pic- ture, &c*." Something like this occurs in moral propofitioris, as, " intemperance is productive of ill * Hanky oa Man, prop. 23. * health,"- Chap. 4.] Commn Satft: . 433 health." Here it is plain that common experience fa frequently unices the confequence to the caufe, that 9mitting all the intermediate fteps neceflary to form the eonclufioB, the mind is fatisfied with the afTertion, and calls it felf-evident. This is what ibme authors (if I am not miftaken) mean by common Jenfe j and in- deed thcfe conclufions are fo generally right, that al- though it may be for the interefts of virtue, occafionally to examine them by the principles of reafoning, men in moft cafes have very little occafion for any other appeal than to their common feelings, to determine on the ju ft ice or injuftice of particular actions j ideas of juftice being founded in the truth of things, and fo con- firmed by experience, that the conclufions are as ready at hand, and almoft as clear as that " the fun (bines ;" " what is, is ;" or any other of thofe maxims that are really felf-evident. On this principle of aflbciation depends the neceflary fucceffion of ideas in a train, -of which any one may fatisfy himfelf by attending to the operations of his own mind. Ideas are introduced by an agreement in fome of the parts of which complex ideas are compofed. Shakefpear, defcribing a merchant's fears, fays, '** l^Iy wind, cooling my broth, " Would blow me to an ague, when I thought " What harm a wind too great might do at fea. *' I fhould not fee the fandy hour*glafs run, " But I (hould think of {hallows and of flats; *' And fee my wealthy Arg'fie dock'd in fand. " Should I go to church, *' And fee the holy edifice of ftone, " And not bethink me ftrait of dangerous rocks * ?" . It is remarked, that the train of ideas almoft always depends upon the relations of contiguity in. time or * Merchant of Venice, fc, i. VOL. Ill, F i place, 434 Train of Ideas. [Book X. place, caufe and effect, refemblance or contrariety j all of which it is obvious, depend on the principles of aflfociation already explained. It has been fully proved, that ideas are affoeiated by contiguity of time j the former impreflion remaining vivid fome moments after it was firft made, and the other during that time occurring, they become united. That aflbciadon which arifes from unity of place is no other than recol- lection, the place making a part of the complex idea of any action. Caufe and efrect are affoeiated by con- tiguity of time ; for, as Mr. Locke oblerves, " we get thefe ideas from our obfervation of the viciffitude of things, while we perceive fome qualities or fubftances begin to exift, and that they receive their exiftence from the due application and operation of other beings *." The relation of refemblance is no other than recollection of that particular idea, in which the object prefent, and the object remembered, agree. When two ideas are formed, agreeing in any quality or qualities, they are faid to be related ; and the degrees of relation are as they agree in fewer or more qualities. Refembiance in one fimple and very common quality, as black, round, &c. will feldom recal an idea, unlefs very recently or very ftrongly imprinted, the mind be- ing confufed with the multitude of objects pqflefling that quality. The aiTcciation of ideas with -their contraries feems to arife, rft, When the idea fo remembered is only a negative idea, and derives its exiftence from its po- fitive; thus cold is the want or decreafe pf heatj ficknefs is rhe want of health j poverty of riches ; &c. ad, When die ideas are connected in point of time *, * Locke, B. ii. c. 26. f " Eye-witnefles generally relate in the order of time, without any exprefs dcfign of doing to." — Hartley on Man, Chap. 4. ] Influence of the Will. 435 as muft be the cafe in a change from one ftate to ano- ther, fuch are the ideas danger zndfafety. 30, Per- haps two things, which are oppofite, being perceived at once, the mind is more forcibly ftruck by each of them, the ideas are conftquyitly more vivid, and more liable to be recollected. The train of ideas is often regulated by fome end propofcd to ourfelves j for where we have an object in view, fuch ideas as are connected with it will of courfe be fuggefled.- By theie means we are frequently im- pofed on ; a pafiion or an intereft will lead on a train of arguments favourable to them, while we imagine we are acting with the utmoft impartiality *. c The indired influence of the will/ fays Dr. Stuart, ff ever the train of our thoughts, is very extenfive. It is exerted chiefly in two ways: — ift, By an effort of attention we can check the fpontaneous courfe of our ideas, and give efficacy to thofe aflbciating princi- ples which prevail in a ftudious and collected mind ; ad, By practice we can ftrengthen a particular aflbci- ating principle to fo great a degree, as to acquire a ^command over a particular clafs of our ideas.' * ' Should any one be furprifed at this dHpofition in our nature to aflbciate any ideas together for the future, which once prcfented themfelves jointly, confidering what great evils, and how much corruption of affections is owing to it, it may help to account for this part of our conftitution, to confider, " that all our language, and much of our memory, depends upon it;" fo that, were there no fuch aflbciations made, we muft lofe the ufe of words, and a great part of our power of recalling paft events, befide many other Valuable powers and arts which depend upon them." Hutchinfon on the faficnij f, i. p. II. Ffa [BookX. CHAP. V. MEMORY*. IJeas of Memory. —Dijlingiiijbed from Ideas of Ima.ginat2on.~-~ fudg- meni concerning Dijlance of Fafls.— 'Memory inytung end old Per - fans. — -ReccUettion. — • Certainty, IT appears, that ideas of memory are diftin- guifhed from ideas of imagination j ift, By being more vivid ; 2dly, By the aflbciated ideas of time, place, and other circumftances that accompany them. As ideas, by being often repeated, become more vivid, it is a common jemarkj that perfons inclined to habits of falfhood, by often repeating the fame ftory, are themfclves at laft impofcd on by the vivacity of the idea, fo as to miftake it for an idea of memory. Mad- men are almoft always deceived in this way. In dreams, the vividnefs of the new fcene, and no aflb- ciated ideas appearing by which to mark thcfe ideas derived from memory, caufe us to miftake them for a feries of real imprefiions. It feems probable, that we judge of the diftance of fafts recorded by the memory, ift, From the idea growing fainter, yet retaining the principal aflbciated circnmftances j idly, From enumerating ideas of fac~bs, which we know, by the order of ideas, to have fuccef- fively happened fmce that point of time in which the idea firft occurred. ' .The death of a friend, or any interefting event, often related, appears to have hap- • « Memory is that faculty by which traces of fenfations ani ideas recur, or are recalled, ia the fame order and proportion, ac- curately or nearly ..as they were once actually prefented.'— Hartley •» Man, lutroduc. pencd Chap. 5.] Why Memory is weak In Childreny &c . 437 pened but yefterday, as we term it, on account of the vividnefs of the idea correfponding to the nature of a recent event *. Miftakes are here prevented in per- fons, who retain their fenfes, by the fecond means of judging, viz. by enumerating fads that have fince oc- curred, &c. Memory is weak in children; ift, Probably, be- caufe the organs are flaccid and weak ; 2dly, For want of a number of ideas, which experience furnimes, and which afterwards ftrengthen the powers of aflbciation. Memory is flow and defective in old perfons; ift, Be- caufe, probably, a rigidity of fibre may render the or- gans of thought lefs active ; sdly, F'ecaufe the paflions are weaker, there is in reality lefs life, of courfe a flug- gifhnefs of mind will generally accompany that ftate. Imprefiions are eafily made on the fenfes of children, but do not remain. On the contrary, it is difficult to • make fuch impreflions on older perfons as to produce ideas, but when made they are lalling. Hence the ne- ceffity of inuring the mind to action and ftudy through every ftage of life, fuch perfons frequently retaining their mental agility and powers longer than others. Ideas are more eafily recollected, ift, By being vU -vidly and diftinctly impreffed ; sdly, By being ftrongly aflbciated. Thefe two caufes will generally concur, for the more vivid an impreffion is, the longer it re^ mains on the fenfe, and of courfe the more ideas it will be aflbciated with. A fentiment when quoted from a book or a poem by another author, as appoiite to his fubjecl:, often makes a more diftinft and vivid impref- fion than in the original writer. The imprefiion is more vivid, becaufe we are apt to fancy that fome pe- culiar excellence induced another author to quote it; it is more vivid too, becaufe it is more diftinct j it is * Hartley on Man, prop. 42. F f 3 better Modes cr Forms cf Memory* [BookX. better remembered, both for this reafon, and becaufe (like all distinct ideas) it becomes affociated with time, place, and other eircumftances, as well as with the ideas of him whd quotes it *. The following are the modes of memory pointed out by Mr. Locke, which may be of fome ufe as de- finitions. f When an idea recurs without the prefence of the object, it is called remembrance ; when fought after by the mind, and brought again in view, it is re- coBt&SKit ; when held there long under attentive confi- deration, it is contemplation ; when ideas float in the mind, without regard or reflexion, it is called re- i^rie-y when the ideas are taken notice of, and, as it were, regiftered in the memory, it is attention -, wnen the mind fixes its view on any one idea, and confiders it on all fides, Jludy j-.' That ideas are commonly recollected in a train has been already noticed. It has, indeed, been difputed, whether we have any further power in recollection, than, tft, Exciting a certain degree of activity in the mind, and awakening it to the different affociations J ; * ' We remember thatbeft, which we underfland moft perfectly. What we underftand, ftrikes us with its whole force : of what we underftand imperfectly, it is only the part underftood that makes any impreffion on us ; of the reft we have no perception ; even that part makes but a faint impreffion. It would acquire additional force from its connexion with the other parts, if the whole were underflood.'— Ger. on Gen. pare ii. f. 9. f Locke, B. ii. c. 19. J « The mention of a perfon often makes us recoiled, that there is fome purpofe for which we want to fee him ; but fometimes, when we cannot call to mind what it particularly is, the fight of that perfon brings it quickly into our thoughts. In confequehce of the fuperior force of fenfations, which enables them to iuggeft conceptions by means of much weaker relations than idtas can, it often happens, that an object occurring to the fenfes gives a very quick and feemingly unaccountable turn to the courfe of the thoughts.'— -Gerrard en Gen. part ii; f. 3. and, Chap. 5.] Means of fir tngthming Memory. 439 and, idly* When two trains of ideas occur, directing the attention to one in preference to the other. The order of time, place, &c. have great influence in re* collection. In recollecting a company, we are obliged to have refpect to the order of place, to the courfe .of.conver- fation, or fome other of the common relations. > Re- collection in order of time happens from Ib'me part of two ideas becoming entangled with each other, as the inind, when waking, is feldom without ibme idea, fb no one is perfectly gone before the introduction of ano- ther. Recollection from place happens by the tranfi- tion which the mind makes from the firft idea to the place, and from the place to the fecond idea • it is the fame in recollection from refemblance. Recol- lection from caufe and effect is the fame as recollection in order of time 3 only it is to be remarked, that we look upon every thing as being both a caufc and effect of fome other thing, though of what, or in what man* ner, we may be ignorant ; and this is the refuk of ex- perience. An idea frequently recollected becomes aftbciated with a number of other ideas in the different repetitions of it ; it will therefore be more predominant, and more apt to be recalled on future occafions ; and this con- ftitutes the power of habit over our turn of thinking, which may be acquired from reading frequently the fame book, orconverfing much with the fame pedbn. Diftinct memory thus depending on affociation, the fimple ideas are often found to remain, while the cir- cumftances firft connected with them are utterly Lft. Thefe the mind forming into new combinations, we call invention. As memory is fo much dependant on aflbciation, k is evident, that what influences the latter will have F f 4 much 44° Connexion of Memory with Organization. [Book X, much effec~b in determining the peculiar excellence of any man's memory. Some are found to have a me- mory adapted to the remembrance of hillorical facts, fome to poetry, &c. Ideas formerly received are fo many hooks (if I may be allowed the exprefilon) that faften on thofe ideas which aflimilate with them. The diitinctnefs, livelinefs, and conne cled circum- 'flances of ideas, leave almoft no room for mifcakes in judgment, as far as depends on die memory. Ideas of memory, by frequent repetition, may be retained equally perfect and vivid as when firft imprinted ; ic follows, therefore, that when, from the clearnefs and vi- vidncfs of the ideas, we feel that they have remained uncoiifufed in the mind, our reafoning, as far as refpeds them, will fall nothing fhort of abfolute certainty. How far the memory is dependant on the corporeal organs, has been often difputed. Some ftriking in- fiances, to prove a very clofe dependance, have been furnifhed by different authors. An Italian poet is re- lated to have fallen dangeroufly ill, and when he reco- vered, to have forgotten the very letters of the alphabet. Pliny fpeaks of a perfon, who, by a dangerous fall, forgot his mother and friends. Meffala Corvinus, by a difeafe, forgot his own name. Valerius Maximus relates, that a citizen of Athens, by a blow of a ftone on the head, forgot all he knew of polite literature, though in other refpects he retained his memory *. In the Memoirs of the Royal Academy, 171 1, there is an account of a young man, who, in a fever, forgot every thing he knew; but afterwards learned very quickly ; fo, retaining his faculties, he loft his former ideas f- * Plin. Nat. Hift. I. vii. c. 24. , f See inftances of extraordinary memory, Plin. Nat Hift. I. vii. c.*4, We Chap. 5«] Extraordinary Powers of Memory. 441 We muft, however, be cautious of giving too im- plicit credit to thefe relations. Authors, as well as all other men, are too fond of the marvellous. It is cer- tain, that the foul or mind of man cannot aft, unlefs the inftruments with which it is to aft are in a proper ftate. The mind is, therefore, affected by the infir- mities of the bodily frame ; yet, in lunacy, and other mental complaints, medicine is found to have but a feeble effeft. That a perfon, from a mere corporeal injury, can have any one fubjeft eradicated from his memory, while he retains others, is not to be believed. Extraordinary and minute powers of memory arc feldom confident with imagination. The mind, in that cafe, feems to be too much occupied with old ideas to be difpofed to form new ones. 1 have heard a gentle- man, of a remarkably ftrong memory, complain, that when he fat down to compofe, he experienced great dif- ficulty, from beinj incumbered with the thoughts, nients, and language of other authors* [ 442 3 [BookX. CHAP. VI. OF INVENTION, Invention', iv?jat.~— Ideas of Memory and Imagination.— In-ventioie akd Judgment. TH E miad m?,y be equally employed in making true as falfe combinations of ideas ; in forming a fyftem, and connecting ideas by their natural relations, as in depicting Centaurs, and making witty allufions ; in either of which cafes it is faid>to invent. In the former there feems to be a greater mixture of judgment, and this kind of invention, is fubfervient to real fcience. On the contrary, when the invention confifts in draw- ing ftrong and lively pictures or reprefentations, either falfe in themfeives, or heightening by rhetoric real facts, it is called imagination ; when it confifts in wild and unexpected combinations, it is called fancy*. From the two laft chapters it appears, that invention is altogether dependant on the principle of aflbciation. When a perfon is poiTerTed of a mind Efficiently active to be eafily affected with the relations pointed out in the preceding chapters, we fay of him, that he has an inventive genius : a quick difcernment of thofe re-^ lations between complex ideas, will lead him to com- bine them into new ones, or to new arrange the order of his thoughts, which will amount to nearly the farre. In an active mind, the ideas will be more vivid, and fuch a mind will take notice of many relations that would * " When ideas, and trains of ideas, occur, or are called up in a vivid manner, and without regard to the order of former a&ual impreflions and perceptions, this is faid to be done by the power of iiragination or fancy."— Hart. Introd. efcape Chap. 6.] Ideas of Imagination & Ideas of Memory. 443 efcape ordinary perfons. When a mind is mere con- verfant, and more affected with the relation of caufei and effect, fuch will conftitute a genius for the fciences* A genius for the arts is more forcibly ftruck with the- relation of refemblance. Hence, firft, it follows, that the memory rriuft be ftrong to fupply a genius for either arts or fciences' with materials for new improvements ; and, 2dly, The mind muft be active, and eafily affected by the feveral relations. The diftindtion between ideas of memory and ideas of imagination has been already mentioned. Ideas of memory muft neceffarily be more lively than ideas of imagination commonly are at firft. Ideas of imagina- tion are only formed from the ideas of memory, fo that at moft the figure is but at fecond- hand, and muft alfa be lefs perfect than what nature has actually prefented to our fenfes. Yet, if we remember what was faid refpecting the frequent repetition of an idea, it will be found, that ideas of imagination may, by this means, become fully as vivid as ideas of memory, which is the cafe with perfons addicted to falfhood, as has been already remarked. But I will even go beyond this, and aflert, that a number of vivid ideas, being com- bined into one complex one, and each having its dependant train of ideas, the complex, or rather de- complex idea, by frequent repetition, will produce a ftronger fenfation than any one of its conftituent parts. Hence it is a felf-evident fact, that the intellectual pleafures and pains, though deducible from the fen- fible ones, are in reality ftronger and more vivid, as any perfbn may fatisfy himfelf who confiders a little the nature of avarice, ambition, or love. It has been cuftomary to eftablifh a radical diftinc- tion between invention and judgment, as if they were 6 diftind 444 Invention *nd Judgment. [Bock X. diftincl: powers of the mind, and not the fame power differently employed; but the only two great diftinc- tions that I perceive in the human mind are, memory and genius, which, it is certain, do not always meet in the fame perfon. Perhaps the reafon they are feldom* found to exift together *, in any confiderable extent, may be a certain inertnefs in minds of the forme read, •which enables them to retain ideas in the grofs, but vrhich difables them from feparating, analizing, or making new combinations. A very vivid mind is not only ftruck with an object as a whole, bwt every con- ftituent part is obferved, and makes, if I may fo ex- prefs it, a feparate impreflion ; thefe parts are, there- fore,- liable to become feparately aflbciated with parts of other complex images, and the fame vividnefs and activity of mind will produce naturally thefe frequent afibciations. * I woul hence the in oft agreeable ideas are united with them, and fo often repeated, that in time the love of mankind becomes, in a manner, a neceflary part of ourfelvesj and from this fource may proceed the focial affections. Difiike and hatred are the oppofites to love, and re- fult from the idea of pain combined with another idea,. A child fhall have no diflike to a certain medicine, till after it has produced naufea, or fome painful fenfation, and thenceforward he will fcarcely hear it named without exprefling his averfion *. The parTions have been analyzed, and thus reduced to loye and hatred by fome of the oldeft writers on the * The idea of pleafure being annexed to a thing, constitutes it, as we fay, good. The idea of pain (either immediate or related) evil. « Thefe (as Mr. Locke obferves) are the hinges on which, the paflions turn." See Locke, b. ii. c. 29. fubjeft 462 Sources of Defire. [Book X. fubject now extant. It is evident, that defjre and aver- fion are the fame paflions made active. Inanimate things may be the objects of love or diflike. fome ex- ternal objeft ; but molt frequently our ideas of beauty arife from, afibciations, as the fenfe of propriety, eafe, &c. &c. •f- " It is evident that gay colours, cf all kinds, are a principal fource of pleafure to young children ; and they feem tt llrike them more particularly, when mixed together in various ways." — Hartley pn Man, Prop. 22. " In adults the pleafure? of colours are very languid in com. parifon of their prefent aggregates of pleafure formed by ailbcia- tion. — Ibid. Green, the middle colour of the feven primary ones, is moft grateful. J Chefelden's Anatomy, p. 301. The boy couched by ChefeU den was mofl pleafed with red, perhaps, becaufc it was the com-, pleteft exertion of his newly acquired faculty. He dreaded black* probably, becaufe it reftored him to his former ilate, and was in (kfl a partial negation of fenfe, Of Chip. II. S (force of the Beautiful in Comptfition, 465 of colour juft mentioned. 4thly, Flowing eafy motion, without that violence which gives a double fenfation of pain, viz. befides the harfn effect to our fenfes, an afibciated pain, by putting ourfelves in the place of the object, fthly, The agitation which a water-fall, a varied profpect, or an high afcent, produces, may be a fource of that kind of pleafure we afcribe to beauty, even independent of the aflbciated ideas. Hence it folloivs, that figures, which pofTefs variety without any thing harm or abrupt, the waving line, running water, and many of thofe conftituents of beauty remarked by painters, are naturally and primarily fuch. Thefe when fo difpofed as not to contradict any attachment efta- blifhed by cuftom, and ftill more when they coincide with it, as when nature is imitated in a fine landlcape, or defcribed in a poem, never fail to give pleafure j and hence it appears, that authors have miftaken who have defcribed that which is moft fit and regular as the mod beautiful. Admitting, in the inftance adduced by Plato *, that the wooden fpoon might be moft ufcful and proper j yet if even the value is fet afide, I apprehend the golden one would be allowed to poflefs the moft intrinfic beauty. The afibciations that arife originally from the plea- fures of fenfe may become fo diftant, that we lofe fight of their origin ; and to an object in this cafe convey- ing pleafure, men univerfally afiign the epithet beauti- ful. Though it is probable, that moft frequently fome of the primary conftituents of beauty will be com- pounded with it, and of this mixed nature are moft of the objects we denominate beautiful, as a fine houfe, a landfcape, a running horfe, &c. On this account it is worth obferving, we often find a whole to pofiefs \ Hippias Maj. VOL. III. H h beauty, 466 Uniformity find Diwrfity of -Tajie^ [Book X. beauty, which by no means refides in the conftituent parts *. The fimple conftituents of beauty have but little influence when put in competition with the defire of gratifying the appetites, or the fear of pain ; to illuftrate this, I (hall only mention auniverfal and com- mon prejudice. There is nothing really deformed in ferpents ; on the contrary, many of the acknowledged conftituents of beauty, fuch as lively colours, variety^ &c. are found in them •, yet from a knowledge of their noxious properties we cannot by any means bring our- felves to view them with that pleasure which beautiful objects ought to infpire. An object which is beautiful will impart a virtue to every thing connected with it. Things prepofterous and deformed in thefnfelves are reconciled to us when worn by a beautiful perfon ; and hence fafhion derives its extenfivc influence. On the contrary, what is worn by ruftics is leiTened in our eftimation by the awkwardncfs of the wearer. Men admire the very defects of their miftrefles, and oftei* judge of beauty by their peculiarities. " Aovatorem quod arnicas '« Turpia decipiunt coecum vitia aut etiam ipfa hxc «« Dele&antj veluti Balbinum polypus Hagrra •}-.'* i Hence we may in a great meafure account for both the uniformity and diverfity of tafte prevalent among mankind. There are fome objects and qualities, which intereft and are pleafmg to every man ; others, with men differently circumftanced, receive a colour from other ideas, with which they may be connected. The human form is the moft pleafmg of all forms to every" * Hippias Maj. ad. fin. f The robe of magiftracy, even when feen on the ftaSge, is- accounted elegant and refptttabk, and fuggefls correfpondent ideas. * man, Chap, ii.] ' Rural Beauties. 467 man, becaufe from fociety he has derived all his choiceft pleafures j but whether white or black is to be preferred, whether an aquiline or aflat nofe, will, per- haps, depend on early aflbciations to determine. The influence of aflbciation over our fenfe of beauty is further obvious in this, that fcarcely any man exifts, who does not annex to particular fets of features good and bad moral ideas j and thefe will probably be drawn from particular perfons. I knew a celebrated painter, whofe beft hiftorical figures all bore fome refemblance to himfelf ; and others have been known, who con- ftantly copied their own wives as the perfection of beauty. Rural beauties are fo compounded of the primary constituents of beauty, united with fo many things that gratify our appetites and fenfes, together with many complex pleafures, fuch as fports and paftimes, the amorous pleafures, &c. that it is no wonder thefe, with the encomiums of others, which have always an influence on imitative animals, ftiould make them die almoft unceafing theme of poets. Of the beauties of art I lhall treat in another chapter. Hha {BookX; CHAP. XII. OF GUSTO M. Fain from Cufism. — P.l?afx.ri.~sl:i>n. TW O obfervations naturally occur, when we con- template the force of cuftora : i ft, That when we. have been long ufed to fee two things together, we do not with perfect pleafure endure to behold them Separate. This is, in truth, a fpecies of difippointment. The idea appears incomplete ; there is a want, and a painful fenfe of want. Thus a cow with but one horn, or a dog with one ear, is a difagreeable object, though, doubtlefs, if they had been created with but one, two would have been accounted a deformity. idly, It is commonly remarked, .that cuftom will make us love almoft any thing, and will reconcile us to almoft any condition. The force of cuftorn here feems to depend entirely on the principle of afTocia- tion. We have already feen that pleafures are more abundant than pains. There is, therefore, fcarcely any Hate in life, which will not be productive of many agreeable ideas; thefe ideas become connected witkr the objects and actions which have occurred, while they have remained imprefled upon the mind ; the idea, therefore, that imparted the pleafure, and the other idea, will become blended together; nay, the fenfe of .pleafure will be transferred from the former to the latter, fo that it may recur united with a fenfe of plea- fure, even when the object that originally imp -ted the pleafure is forgotten. Thus it is n;: ' " ,mmon to Chap. 12.] Sour f 6 of habitual Vices. 469 to hear perfons fpeak in rapturous terms of their paft fituation, when it is impoffible for them to recount the reafons why it was fo agreeable j or, if they were to attempt to recount them, they would probably not aiTign the true caufes. Actions and things in them- < felves indifferent thus borrow pleafures from others, and by this means attach us to them, as we have feen that fafliions, without any one original principle of beauty, nay, even deformed in themfelves, obtain re- Ipeft and admiration from the beaucy of the wearer. It is thus that card-playing, and fome other habitual vices, not in themfelves pleafarrt, acquire an empire over us. The defire of imitating others has, we will fuppofe, been our firft motive for engaging in them; they have been united in the courfe of our purfuing them with the pleafures of fociety, the occafional grar t-ification of avarice, the pleafure of lurprife, &c. and thus afterwards appear pleafajit themfelves from their borrowed luftre. Whether the love of life itfelfis an innate principle has been difputed ; for though infants fear pain, yet they have no apprehenfion of death, till reafbn has fo far made a progrefs, as to inform them that it is connected with pain, and life with happinefs. The love of life is generated from the fenfe of pleafure refulting from the goods we poffefs in it ; and this affords no inconfider- able proof that the good in the world overbalances the evil. So ftrongly, indeed, are the ideas of life and happinefs affociated, that moft men would rather live miferable, than not live at all: thus again we fee that an affociated affection may overcome and coun- teract the natural affections, and even thofe that gave it birth. It will be unneceffary to add any more in this place gp this fubject, or to endeavour^ to prove more at large H b 3 the 47° force of Cujiom. [Book X. the influence of cuftom. To an attentive reader, many facts throughout the remainder of this work will occur to confirm it, and almoft all that has been faid of a lenfe of beauty derived from aflbciation will ap- ply likewife to moral beauty *. It is - oblervable, that every nation and every age has a fafhion in think- ing as well as in drefs j and the whole caft of thinking will be more uniform than men ufually fuppoie. The fports of nations partake of the nature of their govern- ment, and their political prejudices and interefts. Gla- cliators and mock battles were the favourite amufe- ments of the warlike Romans. Men love what is uncommon at firft, becaufe what: produces mental agitation produces pleafure j and there is no paflion produces fo much mental agitation within the limits of pleafure as admiration ; they Afterwards expect a renovation of that pleafure, which was only the effeft of furprifej and often the very recollection, of that pleafure will keep alive the paffion. * " In the reign of Charles II. a degree of licentioufnefs was deemed the charafteriftic of a liberal education. It was connected, according to the notions of thofe times, with generofity, fmcerity, magnanimity, loyalty, and proved that the perfon who acled in this manner, was a gentleman, and not a puritan,"— -Smith's Th. M. S, Pt. 6. f. 2. In the fame manner as you are induced to love and imitate what- ever is connected with a pleafurable or beautiful objecl, you will endeavour to avoid what is connected with pain or deformity. Hence men often aft in extremes. Lord Boiingbroke afTevted, that what firft gave him a diltafte to religion, was the puritanical feverity in his own family. Chap. 13.] [ 47* 3 CHAP. XIII. THE PASSIONS. Of the Pajfiom in general. — Particular PaJJienf. — djfai&tea Paf- Jions.—* Paternal Love. — Sympathy. — Avarice,*— Ambition.*— Lo-ve. IT may prove of the highefl importance in morals to analyze the feveral affections and paffions. The general. caufe has been already traced to the fim- ple fenfe of pleafdre and pain ; we have feen further what it is that is called a fenfe of beauty * ; and now, from the feveral modifications and combinations of thefe, we fhall, perhaps, be able to form at leaft a conjecture how other more complex paffions come to be formed. ' . Love having been proved to proceed from an idea of pleafure combined with another idea, and diflike, or hatred, from an idea of pain combined in the fame manner; dejireznd averfion .have been (hewn to be no other than thefe paffions more actively exerted. Love in the extreme, without defire, is admiration. Defire, when applied to the gratifying of certain natural wants of our bodies, is called appetite. Joy is the pofleffion of a thing loved, a lively fenfe of prefent good. Grief is a fenfe of difappointment, or good loft. Fear is the fenfe of pain, or averfion, united with grief. Anger * "Hartley denominates the paffions, " aggregates of the ideas, or traces of the fenfible pleafures and pains." How they become united into the molt common affections it is our bufinefs to ex- piain. Hh4 is Analyjis of [Book X. is an extreme of averfion, united with a defire of re- moving the object. Revenge is a continuance of anger. Envy is anger excited through the defire of pofiefling what another man is pofleffed of. Hatred is the con- tinuance of envy or refentment. Hope is a mixture of defire and joy. Pride is felf-iatisfaction, and is to ambition what joy is to defire. Contempt is a low de- gree of hatred or averfion, without any mixture of anger or of envy. Curiofity is defire excited by the natural love of action, often ftimulated by appetite, or quickened by the love of beauty. Shame is fear arifmg from the focial affections j that is, a fear of having done fomething that may leflen us in the efteem of others j it is the oppofite of Vqnity. Defrair is nothing but an excefs of grief. Perhaps the annexed fcheme may contribute to elucidate the progrefs of the paffions. PAIN.— Averfion to an irrational objeft— Hatred to a rational objea— -Grief— Fear— Defpair. \ X x irrational objeft— Defire— Love to rational objefls— Joy — Hope — T.xtacy. Chap. 13.] 'ike Paffions. 473 There is fcarcely any fuch thing as a fimple pafilon ^ even thofe which I have here fpecified are generally compounded with each other. Whatever ideas are predominant will determine the bent of the pafiion, much depending on the peculiar tone of the organs at different times. Some paflions more eafily mix than others. Paffions naturally terminate, when their end is ac- complifhed. This, however, does not happen in all caies. It was remarked, that an impreflion, as it is more vivid, remains proportionably longer on the or- gan of fenfe ; all the component fimple parts of it arc more ftrongly imprefied, and it is afTociated with a greater number of ideas, Impreffions accompanied with pain or pleafure are more vivid in proportion to the degrees of pain or pleafure, and fuch we mud re- member are all paflions. Thefe impreflions and ideas are of courfe more vivid than any others, of courfe affociated with a greater number of ideas, all of which will ferve to recall thern, and thus a pafiion becomes the caufe of its own continuance, and by this means in- fluences our train of thinking. From what has been ftated it appears, that paflions are transferable from one object to another. An idea being often repeated with an idea which we love, and which of courfe gives'" u,s pleafure, we come at laft to love the idea which was at firft indifferent. What is more common than to love the children of thofe whom we efteem, and that for no merit p.r beauty in the children themfelves ? In parental love, the paflion is in part transferred from feif to the offspring. The mother, during her pregnancy, connects the idea of the infant in her womb with a number of agreeable ideas, with pleafure and with hope ; hence maternal love is ftronger at firfl than paternal. The idea of duty, 474 Parental Love. [Book X, duty, and the example of others, tend to increafe the paflion ; afterwards cuftom, and the little cares about them. In is obfervable, that the love of parents is weak at firft j but love ruihes in by little afibciations as from a thoufand fources. On this principle depend fome of the ftrongeft affec- tions that fway the human race. Every defire, for in- ftance, is attended with a degree of uneafmefs j to re- move it, therefore, is pleafure. Now, when men once perceive certain agreeable coniequences from obtain- ing an object, a defire of obtaining it enfues ; this de- fire will be liable to be renewed, and will be renewed (imply as a defire, without any retrofpect to the firft motives. This is evidently the cafe in avarice, where, dropping the immediate fteps between money and happinefs, men form a connection, which does by nq means naturally and immediately exift, and love the treafure for its own fake. The fame might be ob- ferved concerning the defire of knowledge, the delight of reading, planting, &c. Thefe were firft entered on •with a view to fome farther end, but at length become habitual amufements ; the idea of pleafure is affociated with them, when the rirft reafon is quite vanifhed out of our minds ; nay, we find this power of affociation fq great, as not only to tranfport our paflions and affec- tions beyond their juft bounds, both as to intenfenefs and duration, but alfo to transfer them to improper objects, and luch as are of a quite different nature from thofe to which our reafon had at firft directed them*.'' I mall clofe this (ketch of the paOions by a fhort account of fympathy or focial affection, and afterwards^ * Preliminary Differtation to Law's Tranflation of King's Origin of Evil. by Chap. 13.] Sympathy. 473 by the hiftory of thofe moft powerful incentives to ac- tion, avarice, ambition, and the paffion of love between the different fexes. The pleafures of fympathy are generated, ift, by that love to our fellow-creatures, which is the effect of early obligation *. adly, Becaufe the fight of any en- joyment excites in us the pleaiurable ideas of that en- joyment, and unlefs envy interferes, thefe will ever have their due effect. Thefe feelings are increafed by the praife that is beftowed on benevolence, &c. and the hope of reward in another life. Sympathy in the mis- fortunes of others has a double effect j when beheld at a diftance, as in theatrical reprefentations, I believe moft men find fomething rather pleafing than otherwife in them, and this arifes from the pleafure that attends moderate emotion, even though derived from a painful fource. In perfons of very delicate fenfations, this affection often degenerates into actual pain ; and on beholding real woe, it is fuch to all who retain the common characteristics of humanity. Companion, or the defire of relieving diilrefs, is no other than a wifh, of removing pain. The fight of a wound excites im- mediately ideas of pain in our minds, and we feel a fen- fation of the fame nature (though weaker) according to our memory of fimiiar pains, or, as we by defcrip- tion judge of them, from the pains that we really have felt. To relieve diftrefs, therefore, is actually taking ofF pain from ourfelves ; to the act of relieving we give the name genera/it}'. The idea of the pleafure is afterwards excited by hearing of an act of generofity, nay, is affo- * The focial pleafures and affe&ions may, as Dr. Hartley pb- ferves, be much indebted for their, increafe to the pleafures of the palate. Since it has been cuflomary in all ages to fatisfy oar ap- ' petites in the company of our neareft connections, the idea of pleafure will become combin,ed with them. elated 476 slvarife. [BookX. dated with the very word itfelf, the mention of which, I believe, in moil people, excites a grateful fenfation. By thefe. means, the virtue of fympathy may tfe con- ftantly maintained, and every amiable pafiien che- rifhed. It has been already intimated whence the paflion of avarice derives its origin. The natural wants of man, it is true, are very few j yet in the prefent ftate of-fo- ciety, thefe wants are not to be fupplied without fome exertions on our own parts. The firft defign, then, of human beings, is, to acquire fuch a competence as will fatisfy the calls of nature. But obferve what habit does. By a continued purflSir, we grow eager in the chace ; the firft object is loft fight of; we annex the idea of pleafure to the means or the inftruments, and fancy riches to have fomcthing in themfelves defirable. A pafiion different from the firft is now generated j one man's example imparrs frefh vigour to another, and the end of life is forgotten in- the ardour of an imagi- nary purfuit *. When the idea of pleafure is once trans- ferred thus to the inftrument, we fee a child prefer a piece of money to many actual gratifications that might be enjoyed immediately. I knew a covetous man, who hired a very uncomfortable large houfe, a third part of which he did not inhabit, becaufe he thought it a good bargain to procure an houfe of that fize at the fame rate as a fmaller. The fame man left a pfeafant farm and a good eftate, and bought a commiflion in the army, purely becaufe he could procure it at a cheap rate. " Avarice is checked, ift, By the ftrong defires of young perfons, and others, after particular gratifications. 2dly, By confidering the infignificance of riches in warding off death and difeafes, alfo lhame and con- * " Ft prapter vitam, vivendi perdere caufas." — Juv. tempt Chap. 13.] Ambition. 47^ tempt in many cafes j and in obtaining the ple.afures of friendfhip, religion, &c. 3d!y, By the eager purfuic of anyparticular end, as learning, fame, &c*." We may obferve, that avarice is only the pafiion of -little minds, and will be chiefly predominant in uncultivated . perfoos, whofe attention cannot be drawn from it by nobler purfuits; and in old people, whofe fenfual paflions are decayed. Ambition feems to be founded, ift, On the hatred or averfion to poverty, and all its concomitant difad- vantages and inconveniencies. sdly, On the experi- ence that we are indebted to our fellow-creatures for many conveniencies of lit* j and from the habit -gerae- rated even in children, of endeavouring to pleafe them, in order to obtain many objects of pleaiure to our fenfes. 3dly, Many of the conftituents of natural and artificial beauty are poflefled by thofe in high ftations, we therefore annex pleafurable ideas to thofe ftations, and love them on that account. 4thly, Cuftom, and the words ufual in commendation, being applied to fuch perfons, increafe the pafiion. Ambition will take a different courfe, according to the difpofition or caft of thinking in different perfons. Thus if a man is habitually fenfual, his ambition will ftill have an inclination towards what may gratify his appetites. One man, -perhaps, from education or ex- ample, has acquired a habit of admiring fine cloaths ; another, from natural timidity, avoids fhame and po- verty. Commonwealths promote ambition of a dif- ferent kind from that which is prevalent in monarchy. Ambition takes a different courfe, according to the time of life. It is to be remarked, that the primary conftituents of this paUion (as indeed in all others) will be obfcured fometimes by the aflbciated affections. f Hartley, prop. 48. The 47 3 Lovt. [BookX. The praile beftowed on the heads of certain fects of philofophers, led many men to defpife the natural objects of ambition, riches and pomp; ahd the natural diflike to poterty and dirt was fubdued and forgotten. The pafiicri of love (and efpecially between refined perfons) is of a very complex nature; and far removed from the fcnfual appetite, with which it is fometimes even very (lightly connected. It is a well known fact, that an accompliihed woman of fortune and family eloped fome years ago with an Italian eunuch, whom {he married for love. The truth is, that befides the appetite, the focial pafllon,'as before explained; and this, heightened by the protection a weaker perfon feems to claim from us -, the ienfe of beauty j admi- ration of particular accomplilhrnents ; the refpect due to high birth or fortune; the commendation of others, and habit, in many refpects concur more or lefs to form the paffion. Men of the world are all of them fenfible what fuccefs may be derived from a pleafurable ftate of mind, in which the object, whom they wifh to pleafe, may happen to be. On this account they ftudioufly mingle in all the pleafures and amufements, of what- ever kind, in which that perfon is found to delight. It is a maxim of Lord Chefterfield, " Make a perfon in love with themfelves, and they are certain to love you in return *." The pleafure of receiving gifts is directly connected with the object that beftows them ; where prefents cannot be made, praife and commenda- tion are the ordinary means, and if their fincerity is * One of our comic writers prefcribes, that a man muft firA make a woman a friend before he ventures to appear as a lover. net Chap. 13.3 Lovt. 479 hot doubted, feldom fail of fuccefs. I queftion not, but it might almoft fecure the fuit of a lover to be the mefienger of fdrne very agreeable piece of intelligence to his miftrefs. Pleafurable ideas, we know, are natu- rally connected with perfonal beauty, riches, high birth, great qualities, or fame. Some impoftors, un- der the mafk of being perfons of rank, have infmuated themfelves into the good graces of females ; nor could the difagreeable ideas naturally annexed to falfhood and deception, afterwards vanquifh the attachment. In fine, if by any means a man can become the afib- ciate of agreeable ideas, on the principles every where proved, I think, throughout this book, he may foon hope to obtain a part in the affections of his miftrefs ; and this may ferve to account, in fome meafure, for the many whimfical connections we are every day wit- nefles of. tf When Mifs delights in her fpinnet, 0 A fidler may a fortune get ; " A. blockhead with melodious voice, " In boarding fchools may have his choice ; *' And oft the dancing matter's art " Climbs from the toe to touch the heart ; " In learning let a nymph delight, " The pedant gets a miftrefs by't *." There is no greater miftakej than that the world is governed by motives of intereft. Cool felf- intereft acts in very few initances. Where mankind are not fwayed by the natural affections, that is, by thofe ideas with which pkafure is naturally connected, they are generally determined by fome prejudice, that is, an idea with which pleafure or pain is fantaftically com- bined. • ' Cademis and Vanefla. There 480 Pra9ic*biBty of Virtue. [Book X. There is, perhaps, no paflion fo improvable by affa- ciation as love ; it is connected with many ideas that tend to refine, foften, and elevate the foul, and to in- creafe the paffion under the appearance of increafmg prefent pleafure. We are not to wonder, therefore, that it has proved fo copious a means of playing with our feelings in poetical and dramatic compofitions. To feel and fympathize v/ith ambition we muft be particularly circumftanced, and then our thoughts are generally roo ftrongly bent on the purfuit to attend to imagination. Ambition is an afbive, love a fedentary palfion. Some conclufions in favour of the practicability of virtue will enfue from the preceding principles, in the firft place, much of the government of the paflions will hence appear to be in our own power, by avoid- ing pernicious afibciations, and by early care j hence we may learn how to reftrain the enthufiafai of avarice and ambition, by tracing them to their fource. In our choice of friends and books alfo, we may learn to be cautious to avoid thofe from which ill habits or pre- judices may be derived ; we may be inftructed further to be aware of the effects of cufcom in acquiring a fondnefs for trifles, and efpecially for gaming, and other unna- tural propenfities ; we may learn to direct our affections to proper objects, to affociate the pleating with the ufe- ful, or, by force of reafon and refolution, to difentangle thofe improper combinations which we may have formed. This, indeed, feems to be the great ufe of reafon and fcience, viz. to enable us to purfue and un- ravel the chain of affociations, which our affections may have extended, and to difcern plainly the Kttleneft of the common and ruling paflions of mankind. Chap. 14.] [ 481 ] CHAP. XIV. OF REASONING*. Common Sen/e; v indeed, the analogy was true in all its parts, a human being would be altogether as fubj'icT: to the laws of inert matter as a blockt>f marble or of wood. What- ever is fubjedl to an abfolute neceffity, can never be the incipient caufe, or the beginner of motion or ac- tion of any kind ; it muft be altogether under the command and direction of external objects ; it muft be altogether inert or paflive, having no principle of action in itfelf. On this account, as I before inti- mated, there would be much more uniformity in the actions of men, if they were fubject to a. fatal influ- ence, then there appears to be; there would be no difficulty in deciding what muft be their conduct in any given circumftances. A freedom of deliberating, chufmg, and determining upon things, is what every man feels in himfelf f. Ic * The arguments by which the atheifts have attempted to prove this analogy, are the moft abfurd and puerile that can well be ima- gined. " Every efFeft," fay they, " muft proceed from fome caufe, and this caufe muft be dependent on another." The direct con- clunon from this is *' that there is no where any origin or be- ginning of motion, but every thing is neceffarily produced by an eternal chain of caufcfc and effects, without any independent ori- gin." Such reafoning as this exaftly refembles that of the Indian, who fuppofes the earth to reft on a crocodile, the erocodile on an elephant — but what does the elephant reft on ? In fadr, to com- pare the operations of the mind to any of the qualities of matter, is to compare, as Dr. Clarke obferves, a fquare to the colour of blue, or a triangle to a found. It is like the blind man, who being afked what idea he had of fcarlet, faid, he fancied it muft be fomething like the found of a drum. •f " As it is in the motions of the body, fo it is in the thoughts of our minds ; where any one is fuch, that we have power to taka Chap. 20.] frm pbyfical Caufe and EfeSt. $ 1 1 is the dictate of nature and common fenfe ; one of the firft perceptions we have of the operations of our own minds. It does not lie with us, therefore, to prove, that the human mind is free ; but it lies with the op- ponents of liberty to prwe, that it is not free ; and this ought to be done upon direct, pofitive, experi- mental evidence, and not upon fanciful analogies of conjecture. The only argument which the fatalifts have ever been able to adduce, which at all bears upon the point, is this — that men act from motives, and thefe motives are dependent upon fituation and external circum- ftances. This, then, is really the point at iflue be- tween the fatalifts, and the advocates for the free agency of man. The former fuppofe the influence of motives from external caufes to be abfolute and unli- mited; the latter allow the influence of the motives to a certain extent, but they deny that it is abfolute and unlimited. In the prefent ftate of human knowledge, it is, in- deed, a fpecies of dogmatifm not to be endured, to pretend precifely to afcertain how far the influence of external motives extends over the mind of man. That external caufes mould have a certain weight and influ- ence with us, is certainly confident with the wifdom of Divine Providence, and confident with that order and regularity which he has every where eftablifhed. If men were to act entirely independent of all influence from external caufes and circumltances, the world would be an entire fcene of confufion and diforder; if, on the con- trary, they were endued with no power of choice or deliberation, the whole would be an inanimate uniform mafs, fubject to certain and definite laws, as much as it up, or lay it by, according to the preference of the mind, there we are at liberty."— Locke's Eflay, B. ii. c. 24. inert 5 i 1 Point at I/ue wifh tit Fstalijls. [Book X. inert matter. In this, therefore, the fame happy me- dium appears to be eftdbliflied as in other inftances. Man, from his natural relation to external things j from that wonderful connection which exifts between the body and the mind, is fubject to a certain influence from fituation and circumftances j but there is dill in his own mind a power of reflecting, deliberating, and de- ciding upon his motives and conduct. Another argument in favour of fatality is deduced from the prefcience of the Deity. " If God foreknov/s all things (it is alleged) then every event muft be predetermined." But this argutrent refts upon the fame prefumptuous foundation as the preceding, which •would pofitively determine the precife degree of in- fuence that external caufes muft have upon the mind of man. Dogmatifm certainly never was the road to truth, and is utterly inconfiftent with that modefty and humility, whicli is the very characteristic of a real phi- lofopher. The prefcience of the Deity ! Who will dare to fay that he is able to define it ? Who will dare to ailege rhat he underilands every particular circum- ftance and attribute of the Divine exiftence ? To fay that God cannot exercife his own powers in that way which is moil agreeable to the ends that infinite wif- dom propofes, and infinite goodnefs would dictate, is, to define and limit omnipotence ! and to affirm that God cannot conftitute man a free agent, c&nnct in this inftance difpenfe with his own prefcience, is to fay, that God is not omnipotent. This was long my own opinion j and I 'was happy to find it confirmed by the excellent and judicious Dr. Henry More, whofe fentiments on this fubject were pointed out to me by a friend. " It is true (fays he) we cannot otherwife think of God's fore- knowledge, but as being every way clear and perfect, and without poffibility of error, as to thofe objects about Chap. 2®.] Divine Preference. 513 about which he judges or pronounces. And furely he does always judge and determine of things according as they are \ that is to fay, of a contingent thing, as it is contingent ; and of a neceflary thing as it is neceflary. Whence it comes to pafs, that thofe things which are contingent and proceed from a free principle of acting, are allowed to be feen by God's confent. " But, not to confine God's omnifdence within nar- rower, nor afcribe to it wider bounds than we do to his omnipotence, which all fuppofe to be an ability to do whatever implies not a contradiction ; let us difpatch the difficulty in a few words, by faying, that the fore- knowledge of contingent effeRs, which proceed from a free -principle of affing, does either imply a contradic- ^ tion, or it does not. If it does imply a contra- ; diction, then fuch effects are not the object of God's omnifdencey nor determined by it, nor rightly fuppofed to be determined at all. But if it does not imply a contradiction, then we actually confefs, that divine pre~ Jcicnce, and bitman freewill, are not inconfiftent, but that they may (land together." The mod decifive argument, however, againft the fatalifts, is, the extravagant conclufions to which this gloonay and comfordefs doctrine leads, and the horrible confequences which are attached to it. If man is a •neteffary agent, he cannot poffibly be an accountable being; for how prepofterous is the thought, how in- confiftent would it be with every principle of juftice, to punifti any being whatever, or in any degree, for what he could not have avoided ? In a theological view, therefore, this doctrine appears to conduct di- rectly to atheifm ; for we cannot conceive of the Deity in fuch a manner as to fuppofe him wantonly cruel or unjuft. To fay that future puniihments are not to be (as the orthodox party conceive) eternal in their dura- tion, does not remove the difficulty j to puni(h at alt VOL. III. L I for 514 Extravagant and Melancholy [Book X, for involuntary offences, is cruelty and injuftice. The fyftem of free agency, on the contrary, is confident \vich all the attributes of God, and is highly confolatory and inftruftive to man. This fyftem refts upon the cleared bafis of juftice. Man is created free.; he has good and evil placed before him, with the ftrongeft and moll conciriating motives in the Chrifdan difpen- fation to purfue the one, and to avoid the other. If he perverfely takes the wrong courfe, and proves in- corrigibly wicked, 'every principle of reafon and equity, fincVions the jnftice of his pnnifliment. — Into the na- ture of that punifhment, it is not our prefent bufincfs to inquire. It wiH donbtlefs be fuch as to fatibfy infi- nite juftice, yet tempered' by the fweet and fakftary ex- ercife of infinite mercy. If the- divine laws are thus outraged by the prepof- tcrous hypothefis of a fatal necefiity ; human laws, I fear, will not ftand upon a much firmer foundation. To punifh any criminal for an error which he could not avoid, is certainly not only cruel, but wicked in the extreme; and yet fuch muft be the cafe, if the doctrine of the fatalifts is true *. * In the courfe of a very few years, it will fcarcely be credited, that 3. bock has been lately published on this very principle, and the argument of the author is briefly this. Man is a neceflary agent, he is therefore not an accountable being; his actions are all determined by his fituation and circumftances, taking in amongft thefe his education and the degree of knowledge he has. been enabled to acquire. What are called crimes therefore are only miftakes, perfectly involuntary on his part, and he therefore (whether he is a thief, a murderer, or a parricide) ought not to ti punijbed, but ivftrufled and reafcned with. As no criminal cught to be punUhed, all laws or regulations mult be perfeft'y nugatory in fociety, and even pernicious ; marriage is law, and therefore it is pernicious, and ought to be abolifned. — It is happy for the caufe of truth, when fuch bocks are published ; for if the farc^ftic genius of a Swift could have more effectually burlefqued the doctrine of neceflity, I am ao judge of irony. On Chap. 20.] Conferences of Fatalifm. $1$ On the whole, it is the part of true philofophy to avoid equally the dangerous extremes of an arrogant dogmatifm, which profeiTes, like the ignorant oppo- nents of Socrates, to know every thing, and of that perplexing fkepticifm which would deprive the human underdanding of capacity and intelligence. As finite: beings, many facts are neceflarily placed beyond the reach of our refearches. They are neither fuited to our faculties, nor our fituation in this life • and where we have rso bafis of fact on which to reafon, error will generally be the confequence of our indulging in vifi- onary {peculations. To confole us for this deficiency, we may (till re- mark, with fatisfaction and gratitude, that if much is concealed, much alfo is known. There is an immenfe fund of practical knowledge perfectly within the grafp of our faculties. There isfcarcely any human fciencej which, to know it well, is not fufficient to employ the mod protracted exiirence of man. I twill be more confident with happkiefs, as well as with modefly, to acquaint ourfelves with thefe, before we launch into the unfathomable abyfs of metaphyfical fpeculation ; nor indeed can any thing be more difgufting, than to hear a loquacious difputant, who is unacquainted with the plained and moil ufeful branches of knowledge, pre- fuming to arraign the appointments of omnifcience, to "re-judge his jufticej" to annihilate the intellectual, and to confufe and difturb the moral world. Much greater is his merit, much founder is his judgment, who fabricates the fimpleft machine, cr plans or exe- cutes the plained undertaking that may be practically ufeful to mankind. Yet we may innocently amufe our curiofityj we may innocently gratify our third of knowledge ; we may innocently exercife our faculties. But let us, in the name 516, Utility recommended. [Book X* name of reafon, exercife them on their proper objects ; let us feek for knowledge where it is really to be found ; let our curiofity employ itfelf where fact, experiment, and obfervation, may lead to fome certain conclufion. The book of nature is open to us ; the material world is difplayed for our infpection, and for our improve- ment ; the intellectual world is covered with an almoft impenetrable veil. What God has chofen to reveal of himfelf in the holy fcriptures, may be eafily compre- hended j what he has chofen for the prefent to keep in referve, no mortal efforts will ever be able to develope. The fimpleft and moft unlearned perfon who ftudies with a pure heart, and an undepraved mind, the facred volume, is practically wifej the brighteft underftand- ing, the moft exalted genius, who attempts to go be- yond it, becomes inevitably a fool. N D E X. A. ABSORPTION, III. 310. Acids, II. 10. • • • animal, III. 78. — — vegetable, III. 41. Adams, Mr. I. 54. Agate, II. 93. Agriculture, III. 32. Air, I. 362. — Balloons, I. 509. Air, alkaline, &c. I. 403. Air, atmofpheric, I. 404. 416. Air, fixed, I. 385. Air gun, I. 431. Air, hepatic, I. 402. Air, inflammable, I. 391. Air, nitrous, I. 397. Air, phlogifticated, I. 382. Air, properties of, I. 416. Air pump, I. 423. Air, vital, I. 371. Alabafter, II. 56. Alkalies, II. 5. Alum, II. 72. Amber, II. 277. Ambition, III. 477. Amethyft, II. 86. Animals, ftrudure of, III. 86. Antimony, II. 143. Argil, 11.71. Arfenic, II. 120. Arteries, III. 240, 241, Arts, III. 487. Albeltos, II. 67. Afphaltum, II. 275. Afibciation, 111.429, VOL. III. Attraction, I. 16. - = — of cohefion, I. 16. - ' capillary, I. 17. - • of combination, 1> 18. Avarice, III; 476. Aurora Borealis, I. 355* Azotic gas, I. 382. Balloons, air, I. 509. Balfams, III. 51. Barbadoes tar, II. 275. Barometer, I. 421. Barytes, If. 49. 69. 70. Bafaltes, II. 106. Battery, electrical, I. 333. Beauty, III. 463. Bell, I.44I. Bifmuth, II. 139.' Black, Dr. his great difcoveries, I. 90, 91. Black lead, II. 262. Bleaching, II. 14. Blood, III. 8 i. - — circulation of, III. 302. Body, human, its growth and decline, III. 412. Boerhaave, I. 89. Boiling, I. 123. Bologniari ftone, I. 167. i8jt' Bones, III. 93. Borax, II. 44. Boyle, I. 2. 87. 98. 164.' Brain, IIL 266* Brafs, II. 154. M m Brea 373- - - 441- 9°- UNIVERSITY OF CALIFORNIA LIBRARY Los Angeles This book is DUE on the last date stamped below. 41584 JRARYQ^ fcmiittrfp ^i33NV-soi^ "^aaAttia^^ — — ^ fcuwasiH^ V\\N)NIVER% ^lOSANCElfj; ^ 3 OFCAIIFO/? 3£^£ % * ^ it 5 v ^ \\EUNIVER% e ^lOS-ANCELfx.> I I ^ 5VM.^— S 'J I 1.-" 1.5 *