THE PROPERTIES OF THR HEART MUSCLE 



171 



the presence of blood within its chambers. Whether or not rhythmicity is 

 a property of heart muscle, as such, was conclusively settled by Gaskell and 

 by numerous later investigators by a very simple process. Gaskell cut thin 



FIG. 168. 



FIG. 169. 



FIG. 168. The Heart of a Frog (Rana esculentd), from the Front. V, Ventricle; Ad, right 

 auricle; As. left auricle; B, bulbus arteriosus, dividing into right and left aortae. (Ecker.) 



FIG. 169. The Heart of a Frog (Rana esculentd), from the Back. s. v., Sinus venosus opened; 

 c. s. s., left vena cava superior; c. s. d., right vena cava superior; c. i., vena cava inferior; v. p., 

 vena pulmonales; A. d., right auricle; A. s. left auricle; A. p., opening of communication between 

 the right auricle and the sinus venosus. X 2^-3. (Ecker.) 



strips of the apex of the ventricle of the terrapin, which is free from the nerve 

 cells, at least nerve ganglia, and found that they contracted rhythmically 

 for hours. This experiment has become a classic one for the study of the car- 



FIG. 170. Automatic Contractions of Sinus Muscle from the Terrapin's Heart in 0.7 per cent 

 Sodium Chloride. Time in minutes. (New figure by L. Frazier.) 



diac muscular tissue. Strips of cardiac muscle cut from the auricle and 

 from the contractile walls of the venae cavse, or sinus venosus, of the terra- 

 pin also contract rhythmically. If the strips of muscle are kept moist with the 

 same blood or serum, then the rhythm of the sinus is greater than that of the 



