1 88 



BIOLOGICAL LECTURES. 



Engelmann illustrates -this by an ingenious model (Fig. 6). 

 A piece of an E string of a violin about 5 cm. long, previously 

 soaked in water, is fastened to the rigid end of the rod a, of 



H 



m 



c 



i 



\^ 



-:» 



a^t^ 



g 



Fig. 6. — Diagrammatic Model of tlie Muscle. (After Engelmann.) 



ab, while the upper end of the string is fixed on the shorter 

 arm of the lever H. To this string different tensions may be 

 imparted by weights d, di. 



Round the string, but without touching it, runs for a length 

 of about 20 mm. and in about 20 curves a spiral of thin plati- 

 num wire. The poles of the wire are connected with two wires 

 coming from the poles of a Grove or Bunsen battery of three 

 or more cells. The whole is immersed in a glass of about 50 

 cc. contents, and filled with water of about 55°-6o° C. A ther- 

 mometer is placed through the aperture of the ebonite cover. 



When no change in the position of the lever occurs, close for 

 some seconds the circuit of the battery through the spiral ; the 

 lever rises. Upon opening the circuit it falls. The thermometer 

 in the glass indicates scarcely any rise in temperature. 



