REPCIRT ON ANIMAL PHYSIOLOGY. 135 



subcarbonate of soda, in order to prevent coagulation of the blood 

 when the extremity of the horizontal portion was introduced into 

 an arter}'. The instrument being so introduced, the mercury 

 was found to oscillate in the parallel branches ; and the degree of 

 oscillation and altitude of the mean point was measured by means 

 of a graduated scale on the long limb, when the instrument was 

 held so that this should be perpendicular. The oscillation was 

 caused b)' the respiration of the animal, the mercury falling on 

 inspiration and rising on expiration. The mid point was found 

 (correction being made for the weight of the column of solution 

 of subcarb. sod. in the short branch,) to stand always at the 

 same place, whatever artery it might be into which the instru- 

 ment was introduced, upon an average of many observations for 

 each ; and gave the height of a column of mercury equal to the 

 mean pressure of the heart, thus shown to exert the same force 

 throughout the whole arterial system. This mean pressure^, mul- 

 tiplied by the area of the aorta, gives the statical force of the left 

 ventricle. 



The mean pressure was found to be in no degree proportional 

 to the weight of the heart, and to differ so little in animals of 

 very unequal size that Poisseuille is disposed to attribute the 

 variations to individual circumstances of health, age, &c. ; and 

 thinks it not unreasonable to conclude that the blood is moved 

 in great and small animals, and in different species, Avith the same 

 force. From such principles it will follow, that the statical force 

 of the heart in different animals will be proportional to the 

 square of the diameter of their aortas. The mean pressure in 

 the Dog, the Horse, the Mare, was between the limits 140 and 

 180 millimetres. Taking the mean of these limits, and measur- 

 ing the aorta, the weight of a column of mercury equal to the 

 statical force of the heart (that with which the blood moves in 

 the aorta) is found in Man to equal 4lbs. 3oz. ; in the Horse, 

 lOlbs. lOoz. The statical force with which the blood movies in 

 the radial artery in man under the same pressure equals half an 

 ounce. 



If the account which I have given of the beat of the pulse be 

 correct, that of the heart against the sides of the chest will de- 

 pend upon the contraction of the ventricles. I ought to men- 

 tion, however, that Corrigan, and Carson, and Burdach are op- 

 posed to this opinion, and rather deduce the beat from the dis- 

 tension of the venti'icles, the contraction of the auricles imme- 

 diately preceding that of the ventricles. The last experiment 

 which I have found on this subject is that of Miiller*, per- 

 formed in conjunction with Prof. Albers. The chest of a Goat 

 * Physiologic, p. 165. 



