426 
membrane. It now returns essentially alter- 
ed, through the pulmonary veins, intothe left or 
jfliore properly posterior auricle ; this cavity 
contracts in the same manner with the , right 
or anterior ; there is a very partial reflux of 
blood into the pulmonary veins, while the 
greater portion is conveyed to the left ven- 
tricle, whence it circulates through all the parts 
of the body ; its return into the auricle being 
prevented by the tricuspid, into the ventricle 
from the aorta by the semilunar valves. 
In the natural course of circulation, the 
above order of successive motions is not pur- 
sued ; for the contraction of both auricles is 
simultaneous, as well as of the ventricles, 
while the dilatation and contraction of the 
auricles and ventricles are alternate to each 
.other. 
The quantity of blood propelled by each ven- 
tricular contraction cannot much exceed two 
ounces ; the force by which the heart acts 
has been made a matter of mathematical cal- 
culations ; but all these calculations, like the 
speculations of the chemical physiologist, 
cannot fail to be erroneous, while the pe- 
culiar nature of the vital force and action is 
disregarded. Keil estimated the power of 
the heart to be some ounces, whild Borelli 
calculates it at 180,000 pounds! 
Dr. Harvey, the discoverer of the circu- 
lation, conceived the whole of the circulatory 
process. to be effected by the heart; in this, 
however, he was erroneous, for the function is 
likewise greatly dependant upon — 
The action of the arteries. These vessels, 
as it respects the number, distribution, and 
coats, have already been described in Ana- 
tomy. It is a remaikable fact, as stated by 
Mr. J. Hunter, that the elastic power is al- 
most the only one with which the parietes of 
the larger arteries are furnished; while in 
those of smaller diameters, muscularity or 
Irritability predominates : and that this last in 
the capillary vessels exists almost exclusive- 
ly. “ '1'hus the passage of the blood into 
the large trunks in the vicinity of the heart 
is principally occasioned by the propulsion 
communicated by this organ ; and the circu- 
lation in the large vessels, as mentioned by 
Lazarius, is rather an hydraulic than a me- 
dical phenomenon ; but in proportion as it 
becomes distant from the centre several 
causes retard it ; and the blood could not ar- 
rive at every part, were not the arteries, 
which are more active in proportion to their 
smallness and distance from the heart, to act 
and propel it towards all the organs.” 
(Richerand.) So erroneous was- the opinion 
of Dr. Harvey. 
The mechanical sources of the blood’s re- 
tardation are, 1st, increase of space occupied 
h’ the arteries ; for the collection of all I 
the branches from a trunk would form a 
larger area than that of the parent branch. 
2d, The resistance made by the curvatures 
of the arteries ; this mechanism, its cause 
and effect, are beautifully illustrated in the 
tortuous course observed in the internal 
carotid which goes to the brain; by such 
mechanism an inordinate How of blood into 
this organ is in a great measure obviated. 
3d, Friction is said to impede the blood’s 
motion; and lastly, its course is retarded by 
the angular distribution of the arterial rami- 
fiyatious. 
e pulse of the arteries is vulgarly attri- 
■PHYSIOLOGY. 
buted to the alternate contractions and dila- 
tations of the heart ; but it is principally oc- 
casioned hv that portion of the blood which 
is propelled into the aorta, coming in cqn- j 
tact with the antecedent columns (for the 1 
arteries are always full), and thus communi- 
cating an impulse; but being obstructed by 
this resistance, it forces itself against the 
sides of the vessels, and gives them their pul- 
satory motion. 
The. pulse is more frequent in children, 
in females, and in persons of much irritabi- j 
lity. In man, and individuals who are cha- 
racterized by strength and regularity of ex- 
citement, it is less frequent but more vigor- 
ous. In early infancy, the pulsations are 
from 120 to 150 in a minute; towards the 
end of the second year, they are about 100 ; 
at puberty 80, manhood 70 to 75, and in 
elderly persons 60 or under. There are 
great varieties in this respect ; Mr.. Astley 
Cooper mentions in his lectures having seen 
an adult with a natural pulse as low as 27, 
and it sometimes is more than 100. 
Capillary vessels. Arteries are described' 
by some physiologists as terminating in anas- 
tomois, in exhalants, in veins, in cellular 
textufe, and in glands ; others view the only 
proper terminations of these vessels to be 
that of their continuation into veins, which 
are connected with the arteries by the inter- 
vention of the capillary vessels. “ The ori- 
gin of the veins is only from the most mi- 
nute extremities of the arteries, which are 
become capillary from the great number of j 
divisions, and return upon themselves with a 
change of structure. 
Dr. Harvey supposed that this- communi- 
cation was effected by an intermediate cellu- 
lar substance ; this, however, is the case only i 
in some parts of the body, as in the placenta, 
the spleen, and corpora cavernosa penis. 
In the capillary vessels the- colour of the 
blood is lost, there not being here a sufficient j 
mass of fluid to circulate such a collection j 
of red globules as is necessary to- constitute 
redness. 
Action' of reins. The venous is much 
more capacious than the arterial system of 
vessels. “ It is estimated that out of twenty- 
eight or thirty pounds of blood, which is about 
the fifth part of the weight of the body in an 
adult man, nine parts are contained in the 
veins, and four only in the arteries.” 
In the arteries the circulation is effected by 
the action of the heart, or of their own mus- 
cular and contractile power;, in the veins, 
however, these circulatory powers have so 
trivial an energy, that nature has guarded 
against impediments in the course of the blood 
through these last, in some instances, indeed, 
lias facilitated this course, by sitch a distribu- 
tion of the vessels as shall ensure an action of 
the muscles in propelling the vital fluid. The 
motion too of the neighbouring arteries as- 
sists the venal circulation, as also the valves, 
in like manner with those of the lymphatics, 
which divide the column of fluid into a num- 
ber of small streams, equivalent to the dia- 
meters of the spaces thus formed. 
Although on account of the comparative 
tardiness of venal circulation, and its not hav- 
ing such obstacles as arterial, there is no pulse 
in the veins,; yet, in the vicinity of the heart, 
a species of undulatory motion is communi- 
cated to these vessels, principally occasioned 
by the reflux of blood before spoken of. 
Demonstrations of the circulation. If am 
artery is opened, the blood is thrown out 
from the side next the heart ; if a vein is 
pierced, the contrary is observed. If, again, 
a ligature is made on an artery, the course 
of the blood is arrested above the ligature; 
if on a vein, below it. Moreover in the semi- 
transparent vessels of frogs and some other 
animals, the direct passage of the blood from, 
the heart to the arteries, and thence to the 
veins, may be actually seen by the aid of a. 
microscope. 
Of the blood. 
The blood circulating in its vessels has the' 
character of an homogeneous fluid ; when se- 
parated, however, from the body, or with- 
drawn from the sphere of vital influence, it 
shortly divides itself into different parts. Im- 
mediately upon separation it exhales a strong 
vapour, to the presence of which have, with 
some inaccuracy of language, been attributed- 
all its vital properties. After remaining a 
short time at rest, the blood separates into 
two distinct parts : the serum, w Inch, accord- 
ing to the experiments of modern chemists, 
holds dissolved albumen, gelatine, soda, phos* 
phat and muriat of soda, nit rat of potash, and 
nniriat of lime ; and the crassamentum, con- 
sisting of the colouring part, which is con- 
sidered as an albumen more oxygenated and. 
more concrescible than that of serum, holding: 
in solution soda, phosphat of lime, and an ex- 
cess of iron. Secondly, of the fibrine, foi merly 
called coagulable lymph, which has a con- 
siderable analogy to muscular fibre, and when 
distilled gives out a great quantity of ammo- 
niacal carbonat. 
.The above principles exist in the blood in. 
a greater or diminished proportion, according, 
to the constitution and health of the in- 
dividual. In pale dropsical habits the serum 
is by far more considerable in quantity than 
its other parts; while the oxygenated albumen,, 
or colouring part (o.ita n ng iron, is under 
these circumstances deficient. In diseases at- 
tended with high excitement, thelibrine is in. 
greatest propo; donate abundance. 
The order w<e have observed would now- 
lead us to describe the respiratory process, 
and the several purposes it serves in the ani- 
mal economy ; to notice in detail the action, 
of the thorax, of the lungs, the alteration of 
air effected by respiration, the consequent 
alteration in the blood, and the disengagement 
of animal heat; for these particulars, how- 
ever, we refer to the article Respiration, 
and proceed to enquire into the function — 
Of secretion. 
Secretion is that process by which is se- 
parated from, the blood-vessels generally, but 
in one or twer instances, directly from the 
lymphatics, every species of animal fluid. 
These are divided by Fourcroy, and other 
physiologists, into, i.st, the saline, as the 
sweat and urine; 2d, the oleaginous, or in- 
flammable, as the fat cerumen of the ears, & c. 
3d, the saponaceous, as bile and milk ; 4th, 
the mucous, as those which are found on 
the surface of the intestines; 5th, the albu- 
minous, among which is classed the serum of 
the blood ; 6th, the fibrous, another part of 
the last-mentioned fluid. 
One of the most important and astonishing 
■facts connected, with secretion is, that from 
precisely the same fluid (the blood), are ela- 
