THE CIRCULATION OF THE BLOOD 



85 



lay the rubber tube across the frog-board myograph and pass a 

 thread from the proximal end of the board around the pulsating 

 tube and thence to the thread-eye of the tracing lever as shown in 

 Fig. 47. 



A block or cork will hold the tube in place. Pulsations of the 

 tube will be transmitted to the thread and in turn to the lever and 

 may be traced upon the kymograph. 



Observations. (1) If the finger be held upon this elastic tube 

 while the bulb is being rhythmically squeezed a series of impulses 

 or pulsations will be felt by the finger. Place one finger upon the 

 elastic tube near the bulb; another finger near the capillary. Let 

 the bulb be pumped with sudden but infrequent contractions. May 

 one note the difference in the time of pulsation felt by the two 

 fingers? If so, which is felt first, and why? What is the cause of 

 the pulsation? 



FIG. 47 







Myograph in use as a pulse-writer : K, kymograph ; L, tracing lever ; S, short arm of elbow 

 lever ; M, section of frog-board myograph ; T, cross-section of rubber tube ; C, block of cork 

 against which the tube rests ; WT, weight-link ; P, pivot. 



(2) To get a tracing of this pulse, pass the rubber tube across the 

 cork board as shown in the figure; adjust to kymograph and take 

 tracing. Vary the character of the bulb contractions as follows, 

 taking one complete rotation of the drum for each variation : 



(a) Slow initial contraction of bulb and slow relaxation. 



(b) Slow initial contraction of bulb and quick relaxation. 



(c) Quick initial contraction of bulb and slow relaxation. 



(d) Quick initial contraction of bulb and quick relaxation. 



(e) Same as (d) with slow rhythm (1 contraction per second). 

 (/) Same as (d) with rapid rhythm (3 contractions per second). 



(3) Make a careful study of these tracings and determine: 



(a) The characteristic and essential features. 



(b) The accidental and non-essential features. 



(c) The cause of the essential features. 



(d) The cause of the non-essential features. 



