254 



THE CIRCULATION OF THE BLOOD 



logical saline in a specimen tube of about i by 3 inches in size, and the 

 arrangement of apparatus figured makes it possible easily and quickly to 

 change this solution for any other that may be desirable. 



Contractions of the ventricular strip in saline usually begin in from 10 to 

 40 minutes after the preparation is made and go through a regular sequence 

 of slight increase in rate and amplitude for from 10 to 20 minutes, followed by 

 a very constant rate, but gradually decreasing amplitude for a period of from 

 2 to 3 hours, figure 171. 



This preparation makes possible many instructive experiments tendino- 

 to show fundamental properties of cardiac muscle. The preparation con- 

 tains no nervous mechanism and its behavior may be safely attributed to 

 the muscle substance itself. 



FIG. 215. Heart of the Terrapin to Show the Method of Cutting the Apex Strip. V, 

 Ventricle; Au, auricles; Vc, venae cavae; Ao, aorta. 



Try the following experiments: Submit the strip to saline solutions of 

 different temperatures, varying through steps of 5 degrees from o C. to 

 40 C. Try the effect of the different ingredients in Ringer's solution; com- 

 bine potassium with saline, figure 172; calcium with saline, figure 173; and 

 potassium, calcium, and saline. Also try Locke's solution; solution of blood 

 diluted with saline; solution of milk with saline in the proportion of one 

 part milk to four of saline. 



Cut and mount strips from the auricle and from the sinus, letting the 

 latter extend out on to the vena cava. In these last preparations care 

 must be taken to balance the lever, as a slight overtension paralyzes the 

 muscle. Immerse these strips in pure serum, compare their behavior with 

 that of the ventricle in pure serum. The sinus and usually the auricle 

 will be found rhythmic in serum, while the ventricle, if it contracts at all, 

 will contract with a very slow rhythm. Often there is a distinct progressive 



