REPORT ON ANIMAL PHYSIOLOGy. 133 



nal canal. In all the invertebral it is placed above the gangli- 

 onic string, and above the abdominal canal*. 



Treviranus has given a table in v/hich the weight of the heart 

 is compared with that of the body, in the different classes of ver- 

 tebral animals. In the Mammalia it varies from ^\j to y^o ; in 

 Birds, from yV to yi^ ; in Amphibia, from ^ io to ^ ig ; in Fishes, 

 from gj-o to y|y. So that, assuming its power to circulate the 

 blood through the body to be in proportion to its weight rela- 

 tively to that of the body, he concludes that its influence de- 

 creases with the descent of the animal in the series f- 



AVhether the arteries in any degree assist the heart in effecting 

 the circulation of the blood, is a question upon which physiolo- 

 gists are by no means agreed. That the heart is able to perform 

 this office alone, is proved by those cases where the circulation 

 in the limb was continued, though the main arteries were com- 

 pletely ossified and incapable of contraction ; and that it does do 

 so in all cases has been inferred, from the fact that there is no 

 systole and diastole observable in the smaller arteries and ca- 

 pillariesj whilst the blood is seen to flow more quickly in the 

 veins on contraction of the heart. Poisseuillet has detailed ex- 

 periments in which he has shown that the artery certainly dilates 

 and contracts under the heart's action, which had been denied 

 by Bichat and Parry, the cause of the pulse assigned by them 

 being a motion of the entire artery in space, without alteration 

 of diameter. By means of a metal cylinder capable of being 

 opened like a box, he surrounded a portion of the carotid artery 

 of a horse with water. A small graduated glass tube projected 

 from the cylinder : the water rose and fell in the tube on expan- 

 sion and contraction of the heart, thus evincing the varying vo- 

 lume of the artery. With another apparatus he measured the 

 recoil of the same artery, having detached a portion of it from 

 the body. A glass tube was fixed to each extremity of the ar- 

 tery laid horizontally. Both tubes then turned perpendicularly 

 downwards for a space ; then one perpendicularly upwards, the 

 other upwards at an angle of 45°. 'The former had a stop-cock 

 at the extremity near the artery, the other at the distant extre- 

 mity. The artery, filled with water, was submitted to a given 

 pressure by mercury and water, which filled the oblique tube, 

 and mercury alone, which balanced it in the other. The artery 

 being thus distended, the stop-cocks were turned. When that 

 at the extremity of the oblique tube was opened, the recoil of the 

 artery caused the mercury to rise in it, and to drive off a portion 



* P'idc Buvdach, vol. iv. p. 451. 



t Erschcinuntjen unci Gesetse des Organischen Lehens, p. 225. 1831. 



X Mnjendie's Journal, vol. ix. p. 48. 



