470 APPENDIX 



unimportant for example, the direction of the current and the relations 

 of the ions bearing it. The more physics the student knows, the better 

 will he grasp physiology, which is largely organic physics and chemistry. 



Didactic Rules for Using the Electrical Apparatus, etc. Dry-cell. 

 This is a modified Leclanche battery-element, the electricity being 

 generated by the action of salammoniac on the zinc plate and conducted 

 inward to the carbon plate by hydrogen and ammonia anions. Hence 

 the carbon, the negative plate, is the positive pole of the cell, and in a 

 conductor completing the circuit outside the cell the current passes from 

 the carbon (anode) to the zinc (cathode). This is an open-circuit cell 

 and its poles must never for a minute be left connected by a conductor 

 when not in use. Each cell has a pressure of more than one volt. 

 Always remove the wire from one of its poles when its use is finished for 

 the day. 



The Inductorium or Induction-coil. The strength of the momentary 

 currents induced in the secondary coil depend on (A) the strength of the 

 battery-make and -break; (B) on the closeness of the two coils to each 

 other; and (C) on the angle between the rings of wire of the two coils 

 (this angle determining the number of the inducing lines of force). The 

 instrument is used in three sorts of ways : (1) to give single make induction- 

 shocks; (2) to give single break induction-shocks; and (3) to produce 

 a current of alternating induced electricity, each double vibration of the 

 automatic armature producing two alterations of this current. To pro- 

 duce single make or break shocks the left-hand binding-post and the 

 middle binding-post are attached to the battery wires, the short-circuiting 

 key left open, and the battery-current made and broken with the simple 

 key. The break induction-shock is stronger than the make induction- 

 shock (because of the absence of the conflicting extra-currents in the 

 primary coil at the break). To produce (3) the alternating current, the 

 right and left corner binding-posts are employed. Stimulation is applied 

 by opening the previously closed short-circuiting-key on the secondary 

 coil while the simple key in the primary or battery circuit is held closed. 

 The short-circuiting key must be kept closed except while using the 

 alternating current in order to avoid explosive tension at the secondary 

 electrodes. Never bend in any way the vibrating filament of the hammer- 

 armature : ask the instructors to make any adjustments which may occa- 

 sionally be necessary. 



When, as is customary, it is desired to stimulate with a make-shock or 

 with a break-shock only, the other in either case must be carefully kept 

 from stimulating, for else two contractions instead of one would be 

 occasioned. To do this, use the short-circuiting key on the secondary 

 coil in the appropriate way. To use a make-shock only: Close the simple 

 key in the circuit (the short-circuiting key being open); this does the 

 stimulating. Hold down the simple key and close meanwhile the short- 

 circuiting key; then release the simple key. To use a break-shock only: 

 Close the short-circuiting key; close the simple key in the circuit and 

 hold it down. Open the short-circuiting key; then on releasing the simple 



