2l6 PRACTICAL PHYSTOLOOY. [XXXTX. 



as fig. 137 will be obtained, where the drum goes round several 

 times before the relaxation is complete. 



(p.) Note that, if the " veratrised " muscle be made to contract 

 several times, the effect passes off— only a simple twitch being 

 obtained — but is re-established after rest. A high temperature 

 also causes it to disappear. 



(/.) The direct action of veratria on muscular tissue may also be 

 studied by the apparatus described in Lesson XLIII., and by this 

 method it is easy to compare the form of the curve before and 

 after the action of the poison (fig. 137). The drum makes many 

 revolutions before the lever comes to the abscissa again. 



{(J.) Investigate the effect of heat and cold in modifying the 

 curves obtained. Under heat the veratria influence passes off. 



LESSON XXXTX. 



ELASTICITY AND EXTENSIBILITY OP MUSCLE— 

 BLIX'S MYOGRAPH. 



1. Extensibility and Elasticity of Muscle. 



(a.) Dissect out the gastrocnemius of a frog with the femur 

 attached, fix the femur in a strong clamp, attach the tendon to a 

 muscle-lever with a scale-pan attached. Neglect the weight of the 

 pan, and see that the lever writes horizontally on a drum. It is 

 better to do the experiment with the sartorius (or with the semi- 

 membranosus and gracilis, Lesson XXIX.), as they have parallel 

 fibres. 



(h.) Place in the scale-pan, successively, different weights (10, 

 20, 30, 40 . . . 100 grams). On adding 10 grams, the lever 

 descends; remove the weight and the lever ascends. Move 

 the drum a certain distance (about 3°), and add 20 grams to the 

 scale-pan. This time the vertical line drawn is longer, indicating 

 greater extension of a muscle by a greater weight, but nevertheless 

 the muscle lever will rise to its original height on removing the 

 weight. Repeat this with other weights. With the heavier 

 Aveights see that everything is securely clamped. If the apices of 

 all the lines obtained be joined, they form a hyperhola. The 

 muscle, therefore, has not a large amount of elasticity, i.e., it is 

 easily extended by Hght weights, and on removal of the weight it 

 regains its original length, so that its elasticity is said to be perfect. 

 The hyperhola obtained shows further that the increase in length 



