46 



PRACTICAL PHYSIOLOGY 



>>o drum is again running at uniform speed 

 take another trace over the first. 



Again swing the lever off the drum 



^'3 by means of the base-piece and then, 



proceeding in the same way, warm the 



j? | muscle by allowing normal saline at 25 



<~ C. to run over it for 2 or 3 minutes, 

 and take another tracing. (Put a plate 

 under the frog-board to catch the solution.} 



&* Number the curves, and note " nor- 



mal," " cold," and " warm " upon them. 



9 Take a time trace, fix, and work out 



| as on p. 41, I. (a), (6), (c) and (d). 



g ,d 4. Effect of Varying the Strength of the 



a Stimulus. 



J-J 1. On the Course of Contraction. 

 gj METHOD. Starting with the lever off 

 "|'S the drum find the smallest stimulus 

 of which will give a contraction, i.e. find 

 .S ^ the furthest point of the secondary coil 

 gj ^ from the primary at which a contraction 

 | can be got. Then take a tracing as 

 "fl w described above and note the position 

 jc 2 of the secondary coil. Now push the 

 ** jg secondary coil nearer the primary, note 

 | | its distance, and take a second record 

 i& when the drum is running at a uniform 

 o g speed. Repeat this, each time moving 

 3 the secondary coil nearer the primary. 

 | | Number the curves and write upon the 

 Zi drum the distance of the secondary coil 

 J from the primary in each. Mark the 

 g ^ point of stimulation, take a time trac- 

 ts ing and fix. Study the effect of varying 

 g-d the strength of the stimulus on (1) the 

 a ^ duration of the phases and (2) the 

 .o extent of contraction. 

 ^ If, with the strongest stimulus used, 

 a shoulder should appear on the ascent 

 | ~ of the curve, consider how it has been 

 g ^ caused. 



<j 2. Ow ^e Extent of Contraction. 



c^~ (1) Disconnect the drum from the 



p.1g g primary circuit, twist the ends of the 



'. g * wires together, and use the mercury 



"* J A ^ e y ^ make and break the current. 



o (2) Bring the lever against the drum 



& unconnected with the driving wheel 



