44

ment, he fufpended the execution of his intended voyage to America.

In the year 1796, he was appointed profeffor in Anderfon's Inftitution at Glasgow, where his lectures were attended in an unparalleled manner. In confequence of this he was invited to read at other places, which not only proved profitable at the time, but alfo gave him great hopes of future fuccefs. This tranfient gleam of profperity, however, foon received a ferious check by the death of Mrs. Garnett, which happened in December 1798. From that time, the remainder of the doctor's life feems to have received very fhort refpites from a feries of unpleafant, and unfortunate

Occurrences.

In 1799, Dr. G. was appointed profeffor of philofophy, chemiftry, and mechanics at the Royal Inflitution, which was at that time established in London. But even in that fituation, which might have been expected to offer a permanent provifion, fortune proved adverfe to him; for a variety of irritating circumftances which he met with in that Inftitu tion, foon induced him to refign his place in it. Thus, being once more left unprovided, he procured a houfe in Great Marlborough Street, and began to read public lectures in it. He was alfo engaged to read lectures at other places; and was at the fame time (1802) elected phyfician to St Mary le Bonne Difpenfary. But this accumulation of employment, however flattering it might be to his hopes, exceeded the powers of his weak conftitution, and in fact his health" fuffered confiderably from it. Yet he might have lived fome years longer, had not a typhous fever, which he caught in the courfe of his attendance at the Difpenfary, put a period to his life on the 28th of June, 1802.

Thus was loft to fociety a man, the ornament of his country, 11 and the general friend of humanity. In his perfonal attachments, he was warm and zealous. In his religion he was fincere, yet liberal to the profeffors of contrary doctrines. In his political principles, he faw no end, but the general good of mankind; and, confcious of the infirmity of human judgment, he never failed to make allowances for error. As a philofopher, and a man of fcience, he was candid, ingenuous, and open to conviction; he never dealt in mystery, or pretended to any fecret in art; he was always ready in explanation, and defirous of affifting every perfon willing to acquire knowledge. Virtue was the bafis of all his actions; fcience never poleiled a fairer fabric, nor did fociety ever fuftain a greater lofs." P. xxi.

Dr. G. ftate's the difficuly of explaining, in a popular courie of lectures, a fubject fo complicated and fo extenfive as that of the animal economy. On this confideration he hopes to obtain the indulgence of his hearers. He adduces feveral arguments to prove the interefting nature of the fubject, and the very great ufe of the inveftigation; fince by the knowledge of phyfiology, i. e. of the proper actions of the parts of the human body, we are enabled to avoid noxious, and to adopt useful practices, for the prefervation of our health, and conflitutions. After these confiderations, the author gives a fhort and comprehenfive, but elegant, view of the human body; namely, of the different parts of which it is composed, the bones, the mufcles, the nerves, the fanguiferous vefiels, the brain, &c; briefly mentioning the principal uses of those parts, their mutual actions, and their dependence upon each other; as well as upon external objects. The latter part of this lecture contains a fketch of the fubfequent lectures..

In the fecond lecture Dr. G. explains the procefs of refpiration, and for this purpofe, he firft defcribes, in a fummary way, those parts of the animal body which are more immediately fubfervient to refpiration; viz. the larynx, the wind pipe, and the lungs. He then ftates the principal properties of the air, and thus fhows that the nature of the atmosphe rical fluid, is the caufe of the admirable effects which are produced in the course of refpiration; fuch as the mainten ance of the animal heat, the abforption of the purest part of the air, which is neceffary for the formation of certain animal fluids; alfo the production of other gafes, and fo forth. This he explains entirely upon that theory of refpiration, which is at prefent almoft univerfally acknowledged by men

of fcience.

All thefe circumftances," this author fays, may be accounted for, by the principle we have laid down; the decompofition of oxygen in the lungs.

"There have not been wanting, however, fome very eminent phyfiologifts, who have contended that animal heat is produced chiefly by the nerves. They have brought forward in proof of this the well known fact, that when the fpinal marrow is injured, the temperature of the body generally becomes diminished; and that in a paralytic limb the heat is lefs than ordinary, though the ftrength and velocity of the pulfe remain the fame. Thefe facts, and others of a fimilar nature, have induced them to believe, that the nervous fyftem is the chief caufe and effential or gan of heat; and they have adduced fimilar arguments, to prove that nutrition is performed by the nerves, for a limb which is paralytic from an injury of the nerves, wastes, though the circu

lation continues. The truth is, that the nerves exert their in Quence upon there, and all other functions of the body, and mo dify their action. The liver fecretes bile, but if the nerves leading to it be destroyed, the fecretion of bile will ceafe; but who will fay, that the bile is fecreted by the nerves? The nitric acid will.

vent, theve metals, and this folution will go on more

quickly if heat be applied; but furely the nitric acid is the fol vent, the heat being only an aiding caufe," P. 31.

The fubje&of the third lecture is the circulation of the blood, and in order to explain this molt important function, Dr. G. begins by defcribing, in his ufual concife and elegant manner, the organs which nature has formed for this purpose, He then fhows how the action of thofe organs, namely, the heart, the arteries, and the veins, forces the blood to move in a conftant circuit through every part of the animal body. This he compares, though not with very friking fimilarity, to the circulation of the aqueous fluid over the furface of the earth.

The principal circumftances which are apt to accelerate, or to retard the ufual circulation of this blood through the fanguiferous veffels, are likewife pointed out in this lecture; and among thefe we find the explanation of a phenomenon which has always been attended with difficulty, and which, however, is fill in want of further examination and illuftration, notwithstanding Dr. Garnett's explanation, which is as follows,

"While we are on this fubject, it may not be improper to take notice of the effects of fwinging on the circulation, which have been found by Dr. Carmichael Smyth, and others, to diminish the ftrength and velocity to fuch a degree, as to bring on fainting. Thefe effects have never been fatisfactorily accounted for; but they would feem to admit of an eafy explanation on mechanical principles: they are undoubtedly owing, at leaf in a great mea fure, to the centrifugal force acquired by the blood.

T

"By a centrifugal force, I mean, the tendency which revolv ing bodies have to fly off from the centre, which arifes from their tendency to move in a ftraight line, agreeably to the laws of motion. Hence a tumbler of water may be whirled in a circle vertically without fpilling it, the centrifugal force pufhing the water against the bottom of the tumbler. In the fame manner when the human body is made to revolve vertically in the arch of a circle, this centrifugal force will propel the blood from the head and heart towards the extremities; hence th circulation of the blood will be weakened, and the energy of the brain diminifhed. The contrary, however, will take place on a horizontal fwing, as I have frequently obferved, both on myfelf and others ;;

Tt4

for

for the centrifugal force in this cafe will propel the blood from the extremities towards the head. P 4010 w war or hist

W

After the above paffage, the author speaks of the spoilation of the arteries, and of the indications arifing from the frequency, the ftrength, the regularity, and other qualities of thofe pulfations. He remarks, that the conclufions concerning the flate of the body, which are derived from thofe peculiar qualities of the pulfations, are frequently wrong, when they are entirely dependent upon obfervation, with out the aid of reafoning. He then lays down certain pol tulates, upon which he grounds his reasoning and his obfervations concerning the above-mentioned indications.

The fourth lecture treats of digeftion and nutrition, toge ther with fome other functions which are more immediately connected with them. This branch of phyfiology is likewife treated in a manner fimilar to the fabjects of the preceding lectures. The parts fubfervient to maftication, fwallowing, and digeftion, are firft defcribed, and then their actions in the proceffes of digeftion, nutrition, &c, are briefly, but very intelligibly explained.

In the fifth lecture, which treats of the fenfes in general, this author endeavours to explain how the human being becomes acquainted with the external world; that is, with the objects which furround him; by means of the senses; for he becomes acquainted with their hardnefs by the fenfe of feeling, of their colours by his fight, of their odoriferous qualities by the fmell, and fo forth.

After fome general obfervations on the powers of the human mind, Dr. G. defcribes the organisms of the fenfes, together with their actions, as far as the prefent flate of knowledge will enable us to understand this most difficult part of phyfiology. In this he proceeds with great regularity and perfpicuity; confidering, in the firft place, the general laws of fenfation, and then proceeding to examine the laws which are peculiar to each fenfe. But ia this lecture the laws peculiar to the touch only are no ticed. The last paragraph of it is here fubjoined.

"Feeling is by far the moft ufeful, extenfive, and important of the fenfes, and may be faid, indeed, to be the bafis of them all. Vifion would be of very little ufe to us, if it were not aided by the fenfe of feeling; we shall afterwards fee that the fame obfer. vation may be applied to the other fenfes. In fhort, it is to this fenfe that we are indebted, either immediately or indirectly, for by far the greateft part of our knowledge; for without it we fhould not be able to procure any idea with refpect to the magni.

tude,

tude, diftance, fhape, heat, hardnefs or foftnefs, afperity or fmoothnefs of bodies; indeed, if we were deprived of this fenfe, it is dif. ficult to say whether we fhould have any idea of the existence of any external bodies; on the contrary, it feems probable that we fhould not." P. 91. 102A

The fenfes of taste and of smell are examined in the fixth lecture; and the feventh treats of found and of hearing, it

The eighth lecture, which is rather longer than any of the preceding, contains the admirable fubject of vifion; and here, in conformity to the other lectures, Dr. G. first deferibes the human eye in all its parts, and then proceeds to explain the nature and properties of light; how vision in general is performed, and in what manner the eye conforms itfelf to fee diftin&tly at different diftances. Concerning what is called the feat of vifion, this author confiders the opinions of the principal philofophers who have bestowed their attention on the fubject, to which he briefly adds his

own,

It is mentioned in almoft every elementary work on natural philofophy or on optics, that there is a place in the bottom of the eye, which is infenfible of light; fo that we cannot perceive that object, the image of which falls exactly on that fpot; fuppofing that the other eye is kept shut This fpot is where the optic nerve enters the eye, and in which place only the choroides is deficient. Speaking of this fpot, Dr. G. fays,

up.

"M. Le Cat, though he ftrenuously fupports Mariotte's opinion, takes notice of a circumftance, which, if he had properly confidered it, might have led him to a contrary conclufion: from a beautiful experiment he obtains data, which enable him with confiderable accuracy to determine the fize of the infenfible fpot in his eye, which he finds to be about or of an inch in diameter, and confequently only about or of the diameter of the optic nerve, that nerve being about of an inch in diameter. I find that in my eye likewife, the diameter of the infenfi. ble fpot is about of an inch, or fomething lefsit Whence it is evident that vifion exifts where the choroid coat is not prefent, and confequently that the choroid coat is not the organ of vifion." P. 151... de fon shy vì vd ei pails » In the fequel, this author likewife takes notice of other interefting queftions refpecting vifion. how y Having thus, in the preceding lectures, taken a view firft ct of the general ftructure, and of the functions of the living body, and then of the fenfes through which we become ac cquainted with the external objects, this judicious author ex