340 OF THE CIRCULATION Of THE BLOOD. 



woorara if artificial respiration be maintained ; on suspending the artifi- 

 cial respiration the mean pressure rises, and curves (Traube's curves) then 

 begin to appear, which gradually become more and more marked, and are 



FIG, 145. 



synchronous with the suppressed respirations ; they are probably partly 

 dependent on the relation of the gases in the blood to the vaso-motor 

 centre, and partly to the direct action of the imperfectly arterialized blood 

 upon the vessels themselves. 



259. The rate of movement of the blood in any artery can only be guessed 

 at as regards the human subject from the comparative results of experiments 

 upon the lower animals ; but several methods have been suggested, by which 

 it may be ascertained in them with some approximation to truth. One of 

 these, employed by Volkmann, aud termed by him the Hsemodromometer, 

 is exhibited in Fig. 146, where A shows the instrument as it is inserted be- 

 tween the two cut extremities of an artery or vein. In this position the 

 blood continues to flow in the original direction ; but by a simple mechan- 

 ical arrangement its course can be suddenly diverted (as in B), through the 

 bent tube filled with serum in the direction of the arrows. The rapidity of 

 the current may be readily estimated by timing its course along the scale at 

 the side. Ludwig has suggested an instrument which he has named a 

 "Stromuhr" or Meter, the principles of which are represented in Fig. 144. 

 This consists of an arched glass vessel with two legs, of which B and c are 

 considerably dilated, aud the extremities of which are inserted into the ves- 

 sels; that directed towards the heart, c, being filled with pure olive oil, whilst 

 the other directed towards the capillaries is filled with defibrinated blood. 

 If the capacity of the limb c up to the point M be known, and the time occu- 

 pied in filling it be noted, it is easy to calculate the quantity of blood passing 

 through the artery in a given period. At D is a mechanical arrangement by 

 which the current of blood through the two limbs may be reversed, and the 

 experiment repeated on the same animal. A third instrument adapted for 

 measuring the rapidity of the blood-current is that represented in Fig. 147, 

 devised by Vierordt, and termed by him the " Hsematochometer." This 

 consists of a small glass cell filled with water, with two mouthpieces lor in- 

 sertion into the vessel, and a light vertically suspended and easily movable 

 pendulum, placed close to the point of entrance of the current from the 

 upper extremity of the divided artery. The amount of deviation from the 

 perpendicular produced by the instreaming blood on the pendulum, as meas- 

 ured by the scale, indicates the velocity of the current. Volkmann gave 

 the rapidity of the stream in the carotid of the Horse as from 12-17 inches 

 per second, and in the Dog, at about 12 inches per second. In the crural 

 artery of the Dog, it had fallen to (5^ inches, and in the metatarsul of the 

 Horse, to 2 inches per second. Vierordt estimated it at 1(H inches per 



