

PERIPHERIC ORGANS OF THE CIRCULATION. 143 



180 to 200 grammes of blood into the system of the arterial 

 cone, the effect of which is to maintain in it a pressure equal 

 to one-fourth or one-fifth of the weight of 

 the atmosphere. The auricle, on the con- 

 trary, being placed at the summit of the 

 venous cone, has the effect, by its relaxa- 

 tion, of diminishing the pressure and nulli- 

 fying it at the extremity of the cone ; we 

 have, indeed, already compared its effect to 

 that produced by blood-letting. There re- 

 sults a gradual lessening of the pressure in 

 the interior of the hydrostatic apparatus 

 formed by the two cones ; this diminution of 

 pressure causes the blood to circulate from 

 the left ventricle to the right auricle : in 

 other words, the want of equilibrium gives 

 rise to a constant current towards the point 

 where the pressure is feeblest. Fig> 42 _ Diagram Ol 



The pressure of the blood, at any point the greater and les- 



t. ^ % i , er circulation.* 



of the circulatory apparatus, corresponds to 

 the distance at which this point is placed from the ventricu- 

 lar and the auricular summit of the double circulatory cone : 

 the pressure is greatest ( or j^ of the atmosphere) at the 

 level of the ventricular summit, that is, in the aorta; in the 

 auricular summit, that is, in the vena cava, it may be said to 

 be (or T J^) of the atmosphere. It will thus be 1 i^ in the 

 capillaries, which are placed half-way between these two, 

 extremities. At any other point in the arteries it may be 

 represented by any number between -ffo and ^^, according 

 to the position of the point under consideration, and the case 

 is the same with regard to the venous cone. Thus, when an 

 artery is opened, especially near its beginning, a jet of blood 

 is seen which rises to a great height (as much as two meters); 

 while from an opening made in the veins the blood only 

 drops, unless artificial pressure is applied, as, for instance, by 

 placing a ligature on the veins (as is done before bleeding 

 the arm). 



* A, Greater circulation. V, Left ventricle. a ? Aorta and its arterial cone, 

 c, c, Capillaries of the body in general, v, Veins which go to form the vena cava 

 (venous cone). 0, Right auricle. 



Bj Lesser circulation. V, Right ventricle, t;', Pulmonary artery, with its 

 divisions (arterial cone of the lesser circulation). c', c', Pulmonary capillaries, 

 a'. Pulmonary veins (venous cone of the lesser circulation). O', Left auricle. 

 (The shaded part of the figure represents that part of the vascular system which 

 is filled with blood from the veins.) 



