[ 334 ] 
PHYSIOLOGY. 
' | 
PHYSIOL'OGY, f. [from the Gr. Qvms, nature, and 
>oyo;, doCtrine.] Implies, in accordance with its deriva¬ 
tion, the whole range of natural philofophy, or the know¬ 
ledge of nature in general f and in this fenfe we find it 
ufed by fome of the ancients Its meaning, however, has, 
in modern times, been reltrifled to a knowledge of the 
ftruClure and functions of the animal and vegetable 
kingdoms. But vulgar or technical language calls by 
this name a hiftory of the funGtions of man while in 
health., leaving his Jiru 6 lure under that divifion of fcience 
called Anatomy, the more general knowledge of the 
funiSHons of animals under that named Zoology, and 
defcribing under Pathology the phenomena of the fame 
functions in a Hate of fuffering or difeafe. See thofe ar¬ 
ticles in this Encyclopaedia. 
The. above-mentioned reftriflion embraces then an en¬ 
quiry into the movements of the wonderful ftrufture of 
man; a fubjeftof all others, except perhaps metaphyfics, 
the moll important and interefting. 
The hiftory of Phyfiology, from its clofe connexion 
with other branches of the healing art, has already re¬ 
ceived ample notice under the article Pathology. The 
opinions of the ancients, the experiments of the moderns, 
and the chief difcoveries of both, have been there fully 
detailed. There remains only, therefore, for the hiftori- 
cal branch of this article, that we fhould notice thofe philo- 
fophic fpeculations, fyllematie works, and general ar¬ 
rangements, which have obtained notice and circulation, 
rather as philofophic than medical fyftems. Thefe could 
not, ofcourfe, be entered into under Pathology, on ac¬ 
count of their extent, their want of immediate influence 
on the practical part of that fcience, and their bearing on, 
and connexion with, zoological refearches. 
The Pythagorean doftrine (the earlieft worth notice) 
confiders man as a microcofm, or an epitome of the uni- 
verfe, in which are produced the fame phenomena as in 
the larger world, only to a lefs extent. The author ad¬ 
mitted more than one intelligent principle, conducting 
all the operations of the human body. He fuppofed that 
the human foul, nouriftied by the blood, fixed by the 
veins, the arteries, and the nerves, as fo many vifible 
frtuations, became obedient to the general luivs of univer- 
fal harmony. He did not pretend that the eternal powers 
of numbers had prefcribed all the phenomena of nature, 
and that the force of numerical harmonies regulated the 
motions of the bodies which filled the univerfe, as he has 
been made to exprefs himfelfby his difciples. But he 
was contented with aflerting, that every thing in nature 
was brought about according to the qualities and propor¬ 
tions of numbers, without attributing to them an intrin- 
iic virtue and a pofitive exiftence. He perceived that the 
phenomena of the animal economy fucceeded each other 
with a ftriCt regularity, by which they concurred in 
maintaining order; and in this order he found the prin¬ 
ciple of the exiftence and prefervation of all beings; a 
principle without which they could not exift. He confi- 
dered the fouls of men as emanations from the general 
foul of the univerfe, or anima nmndi. 
Alcmceon cor.lidered the brain as the feat of the foul. 
He fuppofed found to be produced by the reverberation 
of the air within the cavity of the ear; and he thought 
that tafte was owing to the moifture of the tongue. He 
compared the body of a fcetus to a fponge, which obtain¬ 
ed its nourifhment by the fuClion eftablifned over every 
part of its fubftance. According to him, the motion of 
the blood was the effential principle of life ; and he fup¬ 
pofed that the ftagnation of this fluid in the veins pro¬ 
duced fleep, and its aflive expanfion brought back the 
waking ftate of the body. Health confifted in the equi¬ 
librium and well-proportioned mixture of certain primary 
qualities ; and that, whenever any of thefe became too 
predominant, difeafe was the confequence. 
Empedocles, like the difciples of Pythagoras, fought 
among the properties of numbers for the general princi¬ 
ples both of phyfical and moral fcience. In uniformity 
with this.fyftem it was, that he reckoned the four ele¬ 
ments, and admitted among the particles of thefe mate¬ 
rial principles a kind of afxeflion and averfion, of defire 
and antipathy, capable of l'eparating and reuniting them, 
as occafion might require. He believed that refpiration 
commenced within the uterus, where the infant was pro¬ 
vided from each parent with certain organic particles, 
which tended to unite into one uniform whole. Anax¬ 
agoras, convinced that we muft- attribute the arrange¬ 
ment of matter to the intelligence of a fuperintending 
being, imagined that the body of every animal was formed 
of homogeneous particles, wdiich were brought together 
by a fort of affinity. It appeared to him, that bodies 
which were endowed with thought, were compofed of 
fenfible elements; that thefe elements remained unalter¬ 
able, and that no power in nature could exert any aflion 
on them. 
Democritus explained the principal phenomena of or¬ 
ganized bodies by the affion and re-aftion of atoms, 
which he fuppofed to be endowed with powers eflentially 
aftive, and fufceptible of repelling and attracting each 
other. According to him, generation confifted in the 
cohefion of homogeneous atoms. He conceived the heat 
inherent in the elements of the body to be the foie aftive 
principle with which man was animated ; and that by in- 
creafe of this he became capable of life and motion. He 
beautifully and truly compared the organs of the fenfes to 
mirrors, on which were painted the images of things; and 
he reduced all fenfations to the fenfe of feeling, which he 
fuppofed to be more or lefs delicate according to circum- 
ftances. 
According to Plato, the human body does not contain 
within itfelf the caufe of the phenomena which are the 
confequence or the attendants of life. It is only a paffive 
fubjeft, on which the foul exprefies the feries of its func¬ 
tions, like the canvafs on which the painter traces the.con- 
ceptions of his inventions. He diftinguifhes two princi¬ 
ples of aftion in man : a rational foul, on which depend 
reflection and intelligence; and an irrational foul, on 
which depend life and motion. The latter is difiufed 
through every part of the body; and it is by means ot 
thefe parts that it feels, fuffers pain, or enjoys pleafure. 
Thus, by means of the heart it is fufceptible of courage 
and of paffion: by the liver, of defire. The head is the 
feat of reafon ; the cheft, and efpecially the heart, the 
feat of ftrength and anger; the lungs, the general coolers 
of the body. One divifion of the irrational foul, which 
pofl'efl'es an appetite for food, and all the neceflary re- 
frefhments of the body, is found in the epigaftric region; 
which, in the language of Plato, is a fort of liable, in 
which refides a voracious animal. During nutrition, the 
vital parts affimilate to their fubftance the aliments which 
are prefented to them; and this affimilation is the confe¬ 
quence of an affinity that takes place between thefe parts 
and the nutritious juices. He thus feems to regard nu¬ 
trition as the effefl of a combat between the aliments and 
the parts of the animal. A young animal will receive 
more nouriffiment than one which is old,.becau(e the 
force of its body has more efreft in overcoming the force 
of the nutritious fubftances. 
As the reciprocal aftion of the fold and the body on 
each other did not appear to him capable of being ex¬ 
plained on the fuppofition of immateriality, he propofed 
r the 
