in Anatomy, a musculous part of the animal body, situated in the thorax, on the anterior part of the diaphragm, between the two laminae of the mediastinum, wherein the veins all terminate, and from which all the arteries arise; and which, by its alternate contraction and dilatation, is the chief instrument of the circulation of the blood, and the principle of life. See ANATOMY, No 121, 122.

Several ingenious persons have from time to time attempted to make estimates of the force of the blood in the heart and arteries; who have as widely differed from each other, as they have from the truth, for want of a sufficient number of data to argue upon. This set the truly ingenious Dr Hales upon making proper experiments, in order to ascertain the force of the blood in the veins and arteries of several animals.

If, according to Dr Keil's estimate, the left ventricle of a man's heart throws out in each systole an ounce or 1.638 cubic inches of blood, and the area of the orifice of the aorta be = 0.4187, then dividing the former by this, the quotient 3.9 is the length of the cylinder of blood which is formed in passing through 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: this is at the rate of 1462 feet in an hour. But the systole of the heart being performed in one-third of this time, the velocity of the blood in that instant will be thrice as much, viz. at the rate of 4386 feet in an hour, or 73 feet in a minute. And if the ventricle throws out one ounce in a pulse, then in the 75 pulses of a minute, the quantity of blood will be equal to 4.4 lb. 11 oz. and, in 34 minutes, a quantity equal to a middle-sized man, viz. 1.83 lb. will pass through the heart. But if, with Dr Harvey and Dr Lower, we suppose two ounces of blood, that is, 3.276 cubic inches, to be thrown out at each systole of the ventricles, then the velocity of the blood in entering the orifice of the aorta will be double the former, viz. at the rate of 146 feet in a minute, and a quantity of blood equal to the weight of a man's body will pass in half the time, viz. 17 minutes.

If we suppose, what is probable, that the blood will rise 7+1/2 feet high in a tube fixed to the carotid artery of a man, and that the inward area of the left ventricle of his heart is equal to 15 square inches, these multiplied into 7+1/2 feet, give 1350 cubic inches of blood, which presses on that ventricle, when it first begins to contract, a weight equal to 15.5 pounds.

What the doctor thus calculates, from supposition, with regard to mankind, he actually experimented upon horses, dogs, fallow-does, &c. by fixing tubes in orifices opened in their veins and arteries; by observing the several heights to which the blood rose in these tubes, as they lay on the ground; and by measuring the capacities of the ventricles of the heart and orifices of the arteries. And, that the reader may the more readily compare the said estimates together, he has given a table of them, ranged in the following order. <table> <tr> <th rowspan="2">The several animals.</th> <th colspan="2">Weight of each.</th> <th colspan="2">Height of the blood in the tube from the jugular vein.</th> <th colspan="2">Height of the blood in tubes fixed to arteries.</th> <th colspan="2">Capacity of the left ventricle of the heart.</th> <th colspan="2">Area of the orifice of the aorta.</th> <th colspan="2">Velocity of the blood in the aorta.</th> </tr> <tr> <th>Pounds.</th> <th>Ounces.</th> <th>Feet.</th> <th>Inches.</th> <th>Cubic inches.</th> <th>Square inches.</th> <th>Feet and inches in a minute.</th> <th>Minutes.</th> <th>Pounds.</th> <th>Square inches.</th> <th>Square inches.</th> </tr> <tr> <td>Man</td> <td>160</td> <td></td> <td>7</td> <td>6</td> <td>1.659</td> <td>0.4187</td> <td>56.55</td> <td>34.18</td> <td>4.38</td> <td>51.5</td> <td>75</td> </tr> <tr> <td>Horse 1st</td> <td>8</td> <td>3</td> <td>8</td> <td>3</td> <td>3.318</td> <td></td> <td>113.3</td> <td>17.5</td> <td>9.36</td> <td></td> <td></td> </tr> <tr> <td>Horse 2d</td> <td>9</td> <td>8</td> <td>9</td> <td>8</td> <td></td> <td></td> <td></td> <td></td> <td></td> <td></td> <td></td> </tr> <tr> <td>Ox</td> <td>825</td> <td>12</td> <td>52</td> <td>9</td> <td>10</td> <td>1.036</td> <td>86.85</td> <td>60</td> <td>13.75</td> <td>113.22</td> <td>86.0677</td> <td>0.369</td> </tr> <tr> <td></td> <td>1600</td> <td></td> <td></td> <td></td> <td>12.5</td> <td>1.539</td> <td>76.95</td> <td>88</td> <td>18.14</td> <td>38.0912</td> <td>0.84</td> </tr> <tr> <td>Sheep</td> <td>91</td> <td>5</td> <td>96</td> <td>5</td> <td>8</td> <td>0.172</td> <td>174.5</td> <td>20</td> <td>4.593</td> <td>36.56</td> <td>65.09407</td> <td>0.012</td> </tr> <tr> <td>Doe</td> <td></td> <td>4</td> <td>2</td> <td>9</td> <td></td> <td>0.476</td> <td></td> <td></td> <td></td> <td>0.383</td> <td>0.246</td> </tr> <tr> <td>Dogs 1st</td> <td>52</td> <td>0</td> <td>6</td> <td>8</td> <td>1.172</td> <td>0.196</td> <td>144.77</td> <td>11.9</td> <td>4.34</td> <td>33.61</td> <td>97</td> <td>0.106</td> <td>0.041</td> <td>0.034</td> </tr> <tr> <td>2d</td> <td>24</td> <td>5</td> <td>7</td> <td>2</td> <td>1</td> <td>0.185</td> <td>130.9</td> <td>6.48</td> <td>3.7</td> <td></td> <td></td> <td>0.102</td> <td>0.031</td> <td>0.009</td> </tr> <tr> <td>3d</td> <td>18</td> <td>5</td> <td>4</td> <td>8</td> <td>0.633</td> <td>0.118</td> <td>130</td> <td>7.8</td> <td>2.3</td> <td>19.8</td> <td></td> <td>0.07</td> <td>0.022</td> <td>0.009</td> </tr> <tr> <td>4th</td> <td>12</td> <td>8</td> <td>4</td> <td>3</td> <td>3</td> <td>0.101</td> <td>120</td> <td>6.7</td> <td>1.85</td> <td>11.1</td> <td></td> <td>0.061</td> <td>0.015</td> <td>0.007</td> </tr> </table>