THE RECORDING OF MUSCULAR CONTRACTIONS 33 



method where the muscle is free to shorten and raise a weight so that 

 its tension remains constant throughout (isotonic contraction). 



Action of drugs on muscular contraction. The hyoglossus pre- 

 paration. In a large frog, killed by pithing, cut away the whole of 

 the lower jaw, along with the tongue and hyoid bone. Tie a thread 

 to the tongue near its tip and another near its fixed extremity, and 

 cut this away from the hyoid. The tongue thus separated includes the 

 hyoglossus muscles, which run through it from the hyoid bone, and 

 the preparation can be used in the same way as the gastrocnemius 

 muscle, the hyoid end being fixed by a pin to the myograph cork and 

 the tip connected by its thread with the myograph lever. A smaller 

 weight must be used than in the case of the gastrocnemius, since the 

 hyoglossus muscles are far weaker. Probably the weight of the lever 

 alone will be sufficient. Insert pin-electrodes near the fixed end so 

 that induction shocks will stimulate all the fibres of both hyoglossus 

 muscles. 



If other muscles, such as the sartorius or gastrocnemius, are em- 

 ployed they must be immersed in Ringer's solution (either in a Keith- 

 Lucas muscle-bath (see p. 28) or in the manner shown in Fig. 39 but 

 without the application of heat). The drug is added to the Ringer 

 and allowed to soak into the muscle. 



Veratrin. Arrange the apparatus to take a muscle curve in the 

 usual way. If the speed of the drum is the same as before (one 

 revolution per second), the curve is more prolonged than that of the 

 gastrocnemius, for the contraction of the hyoglossus is slower than 

 that of the gastrocnemius. It is well, however, in investigating the 

 action of veratrin to use a slow rate of cylinder, since this drug enor- 

 mously delays the relaxation of muscle. The cylinder, therefore, should 

 be arranged to revolve once in about ten seconds. 



A normal muscle curve is first described, the point of stimulation 

 being marked in the usual way. Then with a hypodermic syringe 

 a drop or two of veratrin acetate solution (1 in 300) is injected under 

 the mucous membrane of the tongue, so that the drug is brought into 

 contact with the fibres of the hyoglossi. After three minutes take 

 another muscle curve. Describe a time tracing below the abscissa. 

 If the preparation is excited repeatedly, it will be found that the 

 contractions lose their prolonged character, which, however, returns 

 after a period of rest. 



The same method can be used for investigating the action of other 

 drugs upon muscular contraction. 



