R K S 
RET 
R E T 
5/4 
creases; which is not true. The theory, in 
consequence, was abandoned even bv J)r. 
black, himsell: at least he made no attempt 
to support it. , 
^ (.raw ford and Lavoisier, who considered 
ad the changes operated by respiration as 
taking place in the lungs, accounted for 
ihe origin of animal heat almost precisely 
in the same manner with Dr. Black. Ac- 
cording to them the oxygen gas of the air 
combines in the lungs with the hydrogen and 
carbon emitted by the blood. During this 
combination, the oxygen gives out a great 
quantity of caloric, with which it had been 
combined; and this caloric is not onlv suf- 
ficient to support the temperature of the 
body, but also to carry off the new-formed 
water in the state of vapour, and to raise 
considerably the temperature of the air in- 
spired. According to these philosophers, 
then, the whole of the caloric which supports 
the temperature of the body is evolved in 
the lungs. Their theory accordingly was 
liable to the same objection with Dr. Black’s ; 
but they obviated it in the following man- 
ner: Dr. Crawford found, that the specific 
caloric of arterial blood was 1 . 0300 , while 
that ot venous blond was only 0 . 8923 . lienee 
he concluded, that the instant venous blood 
is changed into arterial blood, its specific 
caloric increases; consequently it requires 
an additional quantity of caloric to keep its 
temperature as high as it had been while ve- 
nous blood. '1'his addition is so great, that 
the whole new caloric evolved is employed ; 
the temperature of the lungs must necessari- 
ly remain the same as that of the rest of the 
body. During the circulation, arterial 
blood is gradually converted into venous ; 
consequently its specific caloric diminishes, 
and it must give out heat. This is the rea- 
son that the temperature of the extreme parts 
of the body does not diminish. 
This explanation is certainly ingenious, 
but it is not quite satisfactory : for the dif- 
ference in the specific caloric, granting it to 
be accurate, is too small to account for the 
great quantity of heat which must be evolved. 
If is evident that it must fall to the ground 
altogether, provided, as we have seen reason 
to suppose, that the carbonic acid gas and 
w ater are not formed in the lungs, but during 
the circulation. 
Since the air enters the blood, and com- 
bines with it in the state of gas, it is evident 
that it will only part at first with some of its 
caloric ; and this portion is chielly employed 
in carrying off the carbonic acid gas, the 
azotic gas, and the water. For the reason 
that the carbonic acid leaves the blood 
at the instant that the air enters it, seems to 
be this : The air combines with the blood, 
and pari of its caloric unites at the same in- 
stant to the carbonic acid, and converts it 
into gas: another portion converts the wa- 
ter into vapour. The rest of the caloric is 
evolved during the circulation, when the 
oxygen of the air combines with hydrogen 
and carbon, and forms water and carbonic 
acid gas. The quantity of caloric evolved in 
the lungs seems not only sufficient to carry 
off the carbonic acid and water, which the 
diminution of the specific caloric must facili- 
tate ; but it seems also to raise the temper- 
ature of the blood a little higher than it was 
before. For Mr. John Hunter constantly 
found, that the heat of the heart in animals 
was a degree higher than any other part of 
the body which lie examined. Now tills 
could scarcely happen, unless the tempera- 
ture of the blood was somewhat raised during 
respiration. 
d ims we have seen two uses which respir- 
ation seems to serve. The first is the com- 
pletion of blood by. the formation of fibrina ; 
the second is the maintaining of the temper- 
ature of the body at a particular standard, 
notwithstanding the heat which is continually 
giving out to the colder surrounding bodies. 
But there is a third purpose, which explains 
why the animal is killed so suddenly when 
respiration is stopped. The circulation of 
the blood is absolutely necessary for the 
continuance of life. Now the blood is cir- 
culated in a great measure by the alternate 
contractions of the heart. It is necessary 
that the heart should contract regularly, 
otherwise the circulation could not go on. But 
the heart is stimulated to contract by the 
blood : and unless blood is made to undergo 
the change produced by respiration, it ceases 
almost instantaneously -to stimulate. As the 
blood receives oxygen in the lungs, we may 
conclude that the presence of oxygen is ne- 
cessary to its stimulating power. 
REST, the continuance of a body in the 
same place, or its continual application or 
contiguity to the same parts of the ambient 
or contiguous -bodies ; and, therefore, is 
opposed to motion. See Motion. 
Rest, in music, the same with pause. 
RESTAl RATION, in architecture, the 
act of repairing t hose parts of a building that 
are gone to decay, in such a manner as to 
give it its original strength and beauty. See 
Architecture. 
RESTIO, a genus of the triandria order, 
in the dicecia class of plants. The male calyx 
is an ovate spike of membranaceous scales ; 
the corolla is proper, hexapetalous, and per- 
sistent. The female calyx and corolla are as 
in the male ; the germen is roundish, and 
is sex-sulcated ; there are three erect and 
persistent styles; the capsule is roundish, 
with six plaits, and is rostrated and trilocular; 
the seeds are oblong and cylindrical. There 
are twenty-eight species, all natives of the 
Cape, some of them resembling rushes ; and 
used for making brooms, thatching houses, 
&c. 
RESTITUTION, of medals. See Me- 
dal. 
RESTORATIVE. See Medicine, and 
Materia Medica. 
RETAINER, in law, a servant who does 
not continually dwell in the house of his 
master, but only attends upon special occa- 
sions. 
RETAINING fee, tlie first fee given to 
a serjeant or counsellor at law, in order to 
make him sure, and prevent his pleading on 
the contrary side. 
RETARDATION, in physics, the act of 
diminishing the velocity of a moving body. 
See Resistance. 
RETE mirabile, in anatomy, a small 
plexus, or net-work, of vessels in the brain, 
surrounding the pituitary gland. See Ana- 
tomy. 
Rete mucosum. See Cutis. 
RETENTION, is defined, by Mr. Locke, 
to be a faculty of the mind, whereby it keeps 
or retains those simple ideas it has once re 
ceived by sensation or reflection. 
Retention, is also used in medicine, &c. 
for the state of contraction in the solids or 
vascular parts of the body, which makes 
them hold fast their proper contents. In this 
sense retention is opposed to evacuation and 
excretion. 
RETICULA, or Reticule, in astrono- 
my, a contrivance for the exact measuring 
the quantity of eclipses: 
1 he reticule is a little* frame, consisting 
of thirteen fine silken threads, equidistant 
from each other, and parallel, placed in the 
focus of object-glasses of telescopes ; that is, 
in the place where the image of ihe lumi- 
nary is painted m its full extent ; of conse- 
quence*, therefore, the diameter of the sun 
or moon is seen divided into twelve equal 
parts or digits; so that ‘to find the quantity 
of the eclipse, there is nothing to do but to 
number the luminous and the dark parts 
As a square reticule is only proper for the 
diameter, not for the circumference, of the 
luminary, it is sometimes made circular by 
drawrng six concentric equidistant circles. 
This represents the phases of the eclipse 
perfectly. 
REilNA, in anatomy, the expansion of 
the optic nerve on the internal surface of the 
eye, whereupon the images of objects beina- 
painted, are impressed, and by that means 
conveyed to ihe common sensory in the 
brain, where the mind views and' contem- 
plates their ideas. See Optics. 
RETORT, in chemistry, a kind of hollow 
spherical vessel. See Chemistry. 
RE l RAXI T, in law, is where a plaintiff 
comes in person to the court where his ac- 
tion is brought, and declares lie will not 
proceed in it, in which case the action is 
barred for ever. A retraxit differs from a non- 
suit in this, that it is always where the plaintiff 
or demandant is personally in court. See 
Nonsuit. 
RE I R RNCHMENT, in the art of war, 
any kind of work raised to cover a post, and 
fortify it against the enemy, such as fascines 
loaded with earth, gabions', barrels of earths, 
sandbags, and generally all things that can 
cover the men and stop the enemy. But 
retrenchment is more particularly applicable 
to a fosse bordered with a parapet ; and a 
post fortified thus is called post retrenched, 
or strong post. 
Retrenchments are cither general or par- 
ticular : general retrenchments are new for- 
tifications made in a place besieged, to cover 
the besiegers when the enemy become mas- 
ters of a lodgment on the fortification, that 
they may be in a condition of disputing the 
ground inch by inch, and putting a stop to 
the enemy’s progress in expectation of re- 
lief. 
RETROGR ADATION, or Retrogres- 
sion, the act or effect of a thing moving 
backwards. 
The retrograde motion of the planets is an 
apparent motion, whereby they seem, to an 
observer placed on the earth, to move back- 
wards, or contrary to the signs. See Astro- 
nomy. 
RETURN, returna, or retorna, in law, is 
used in divers senses. 1. Return of writs by 
sheriffs and bailiffs is a certificate . made by 
them to the court, of what they have done 
in relation to the execution of the writ di- 
