H E A
681
HE A
i
possible, in sea-water; but, where that cannot be procured, dis-solve an ounce of salt in a bason of water, and wash the skin withthe solution, after which put on the clothes without drying theSkin. This operation strengthens the muscular fibres, and coversthe skin with a kind of saline crust, which, in the opinion of Dr.Hales, effectually prevents all febrile infections. With these pre-cautions, he asserts, a person of a sound constitution may enjoy asgood a state of health in the hottest as in the most temperate cli-mates.
II'BEARING, a sensation , whereby, from a due motion impress-ed on the fibrillar of the auditory nerve, and communicated thenceto the sensory, the mind perceives and gets the idea of sounds.See Anatomy and Acoustics.
HEART , \_heort, Sax. hertz, German,] the muscle which byits contraction and dilatation propels the blood through the courseof circulation, and is therefore considered as the source of vitalmotion. See Anatomy.
Heart, Experiments to ascertain the Force of theBlood in the. Physiologists and Anatomists have from timeto time attempted to make estimates of the force of the blood inthe heart and arteries; but have differed as widely from eachother, as they have from the truth, for want of sufficient data.This set the ingenious Dr. Hales upon making prop hr experi-ments, to ascertain the force of the blood in the veins and arteriesof several animals. If, according to Dr. Keil’s estimate, the leftventricle of a man’s heart throws out in each systole an ounce or1.638 cubic inches of blood, and the area of the orifice of the aortabe =0.4187, then dividing the former by this, the quotient 3.9 isthe length of the cylinder of blood which is formed in passingthrough the aorta in each systole of the ventricle; and in the 75
pulses of a minute, a cylinder of 292.5 inches in length will pass jthis is at the rale of 1462 feet in an hour. But the systole of theheart being performed in one-third of this time, the velocity of theblood in that instant will be thrice as much, viz. at the rate of4386 feet in an hour, or 73 feet in a minute. And if the ventriclethrows out one ounce in a pulse, then in the 75 pulses of a minute,the quantity of blood will be equal to 4.4 pounds 11 ounces, and,in 34 minutes, a quantity equal to a middle-sized man, viz. I5Spounds will pass through the heart. But if, with Dr. Harvey andDr. Lower, we suppose 2 ounces of blood, that is, 3.276 cubicinches, to be thrown out at each systole of the ventricle, then thevelocity of the blood in entering the orifice of the aorta will bedouble the former, viz. at the rate of 146 feet in a minute, and aquantity' of blood equal to the weight of a man’s body will pass inhalf the time, viz. 17 minutes. If we suppose, what is probable,that the blood will rise 7 + 4 feet high in a tube fixed to the ca-rotid artery of a man, and that the inward area of the left ventri-cle of his heart is equal to 15 square inches, these, multiplied into7 + 4 feet, give 1350 cubic inches of blood, which presses on thatventricle, when it first begins to contract a weight equal to 15.5pounds. What Dr. Hales thus calculated from supposition, withregard to mankind, he actually experimented upon horses, dogs,faliow-does, &c. by fixing tubes in orifices opened in their veinsand arteries ; by observing the several heights to which the bloodrose in these tubes as they lay on the ground ; and by measuringthe capacities of the ventricles of the heart and orifices of the ar-teries. And, that the reader may the more readily compare thesaid estimates together, he has given a table of them, ranged iuthe following order ;
The several animals.
Weight of each.
Height of the blood in thetube from the jugularvein.
Height of the blood in tubesfixed to arteries.
Capacity of the left ventri-cle of the heart.
Area of the orifice of theaorta.
Velocity' of the blood in theaorta.
Quantities of blood equalto the weight of the ani-mal, in what time.
1
How much in a minute.
Weight of the blood sus-1 tained in the left ventri-
j cle contracting.
N° of pulses in a minute.
Area of transverse section ofdescending aorta.
Area of the transverse sec-
tion of ascending aorta.
Pounds.
Inches.
Feet.
Inches.
Cubic inches.
Square inches.
i
Feet and inchesin a minute.
Minutes.
Pounds.
Pounds.
Square inches.
Square inches.
Man
160
On
7 6
1.659
0.4187
56.65
34.18
8.32
51.5
75
straining.
4.318
113.3
17.5
9.36
Horse 1st
8 3
2d
9 8
3d
825
12 52
9 6
10
1.036
86.85
60
13.75
113.22
86
0.677
0.369
Ox
1600
12.5
1.539
76.95
88
18.14
38
0.912
0.84
right, left.
Sheep
91
54 9
6 5|-
1.85
0.172
174.5
20
■ 4.593
36.56
65
0.094
0.07 0.012
Doe
4 2
9
0.476
0.383
0.246
right, left.
Dog 1 st
52
0 6
6 8
1.172
0.196
144.7
11.9
4.34
33.61
97
0.106
0.041 0.034
2d
24
5 7
2 8
1
0.185
130.9
6.48
3.7
0.102
0.031 0.00b
-3d
18
5
4 8
0.633
0.118
130
7.8
2.3
19.8
0.07
0.022 0.00b
-4 th
124
4
3 3
f
i
0.5
0.101
120
6.7
1.85
11.1
0.061
0.015 o.oo;
voL.ii.— no. ivi. o a- Hearth