2i4 PRACTICAL PHYSIOLOGY. [XXXVIII. 



in the result. The contraction is both much longer and lower, and 

 tlie latent period is also longer. 



('•.) Pour on to the muscle warm salt solution and take another 

 tracing. Observe the result. Do not overheat the muscle or heat- 

 rigor results (fig. 134). 



Other Methods, — {d.) Adjust a piece of wire gauze over the leg, and allow 

 it to project beyond the end of the plate ot the myogra})h. Heat the gau?* 

 with a spirit-lamp. Take a tracing. The contraction is shorter than in 1 

 {h. ). Do not overheat the muscle. 



(g.) A piece of lead-piping of narrow diameter (J inch) can be bsnt into the 

 form of a cylinder, and the muscle placed within it. Water of various 

 temperatures can then be passed through it. 



(/. ) The muscle may be attached to an ordinary horizontal writing-lever. 

 Surround the muscle with a double-walled box, with an inflow and outflow 

 tube, through which water at diff'erent temperatures can be passed. A 

 delicate thermometer is placed in the chamber with the muscle. 



(g.) A convenient method is to allow the muscle to rest on a small circular 

 brass box, fitted into the wooden plate of the crank-myograph. The box (B, 

 B) is provided with an inflow and an outflow tube, through which water of 

 the desired temperatuie can be passed. 



S^Q^^C^^'^^^^'^^^ 



250 OV. 



Fig. 135.— Pendulum-ilyograph Curves, showing the Influence of the Load on 

 the Form of the Curve. 



2. Influence of Load on Form of Muscle-Curve. 



(a.) Arrange an experiment with the pendulum-myograph as in 

 Lesson XXXVII., using either a muscle-lever or a crank-myograph. 

 Or, arrange a crank-myograph (after-loaded) to write on a cylinder, 

 the cylinder being arranged to break automatically the primary 

 circuit as at p. 202. Take all the curves on the same base line. 



(b.) Take a tracing with the muscle weighted with the level 

 only. 



(c.) Then load the lever successively with different weights (5, 20, 

 50, 70 ... 100 grams), and in each case record a curve and observe 

 how the form of the curve varies (fig. 135). 



('/.) In each case record the abscissa and time-curve. 



3. Influence of Veratria on Contraction. 



(a.) Destroy the brain of a frog, and inject into the ventral 

 lymph-sac a few drops of a i p.c. solution of sulphate of veratria. 



