104 GENERAL PROPERTIES OF LIVING TISSUES 



cause fatigue. A peristaltic contraction wave 

 usually passes from the anode in both directions 

 along the intestine. 



Place the cathode on the intestine, and the 

 anode on an indifferent point. Close the key. 



A small, indistinct thickening will be seen in 

 the cathodal region. 



Thus the intestine, while it serves admirably to 

 illustrate a polar action of the galvanic current, ap- 

 parently differs from the tissues already considered 

 in that closure causes contraction at the anode in- 

 stead of the cathode. The exception is only appar- 

 ent, and its explanation is that the point at which 

 the electrode touches the peritoneal surface of the 

 many-layered intestinal wall is not the physiologi- 

 cal anode or cathode ; i. e. not the point at which 

 the current actually enters or leaves the muscular 

 coat. This matter is discussed on page 110. 



5. Smoke a drum. Eaise the drum off the fric- 

 tion bearing by turning the screw at the top of the 

 shaft to the right. Arrange two muscle levers 1 

 and the electro-magnetic signal (Fig. 27) to write 

 on the drum in the same vertical line. Place the 

 electro-magnetic signal, together with a simple 

 key, in the circuit between one dry cell and the 

 rheochord. Bring the slider near the positive 

 post of the rheochord. 



1 Or heart levers (Fig. 53, page 311). 



