12 



ELEMENTARY PHYSIOLOGY. I. 



comes again in contact with c and the cycle of events 

 starts again. 



In some induction coils there is a central pillar as 



Fig. 5. The extra pillar is for the purpose of equalising approximately 

 the make and break currents. Screw c is raised out of reach of the 

 vibrator, screw / is raised till it nearly touches it. A thick wire is 

 connected with the upper binding screw on pillar a, and with the 

 top binding screw of the primary coil. Thus when the vibrator is 

 draw down it comes in contact with / and the greater part of the 

 current ceases to pass through the primary coil. Since, however, 

 the circuit of the primary coil is still complete, the extra current 

 decreases the rate of electrical change at the 'break' to approxi- 

 mately the same extent as it does at the 'make.' 



in Fig. 5. For ordinary use this is not required, and the 

 screw / should be lowered out of range of the vibrator. 



5. A leg of a frog is given you. Tear off the skin. 

 Sketch the anterior and posterior surfaces, marking the 



