206 



PRACTICAL PHYSIOLOGY. 



[xxxvn. 



(c.) To determine the greatest amount of work obtainable, 

 various heights must be tried to get the largest product, care 

 being taken not to fatigue the muscle. 



4. Curve of Heat-Eigor. (a. ) 

 Arrange a frog's gastrocnemius to 

 record by means of a crank-myo- 

 graph on a slow-revolving drum, 

 weighting it with 30-50 grams. 

 Inscribe the continuous change of 

 form of the muscle produced by 

 pouring water at 70 C. on the 

 muscle. 



(b.) Or, use the following appa- 

 ratus devised by Ludwig, where, 

 however, the sartorius is used in 

 place of the gastrocnemius, as it 

 has parallel fibres (fig. 124). 



5. Chordogram. Engelmann 

 (Croonian Lecture, R. S. 1895) has 

 shown that, when a short length 

 (5 cm.) of an E violin string, pre- 

 viously swollen in water, is fixed 

 so as to record any alteration in 

 its length, on suddenly heating the 



FIG. 124. Apparatus for obtaining the curve string the lever rises, and on cool- 

 of a sartorius in heat-rigor. ing the lever falls and a curve is 



recorded just like a contraction 



curve of muscle. Or a string may be made to swell by dipping in hot water 

 and then soaking in concentrated glycerin. This can then be heated in air 

 and the movements recorded. 



LESSON XXXVII. 



PENDULUM-MYOGRAPH SPRING-MYO GRAPH 

 DESPRETZ SIGNAL. 



1. Pendulum-Myograph Muscle-Curve. 



(a.) Cover the oblong glass plate with glazed paper, smoke its 

 surface, and fix it to the pendulum. The plate must be so adjusted 

 that the pendulum, on being set free from the "detent" (fig. 125, 

 C), shall be held by the " catch" (C). Test this. 



(b.) Arrange the primary circuit for single shocks as in fig. 125, 

 interposing the trigger-key or knock-over key of the pendulum- 

 myograph (K')'. Short-circuit the secondary coil. 



(c.) Fix the femur of a nerve-muscle preparation in the clamp, 

 attach the tendo Achillis to the writing-lever (S), and place the 



