492 MUSCLE-NERVE PHYSIOLOGY 



the muscles which guard the orifice (rima glottidis) by which it escapes, and of 

 those (of tongue, palate, etc.) which modulate the sound to the form of speech. 

 Over either of the groups of muscles, by itself, a stammerer may have as much 

 power as other persons, but he cannot harmoniously arrange their con- 

 joint actions. 



LABORATORY EXPERIMENTS ON MUSCLE AND NERVES. 



Physiological experiments on living muscle serve to demonstrate many 

 of the most fundamental particulars of the subject. The muscles, especially 

 of cold-blooded animals, when isolated from the body retain their living 

 attributes for several hours under the ordinary conditions which can be readily 

 supplied in the laboratory. They, therefore, serve as specially favorable 

 experimental material. 



The muscles of frogs, turtles, and other cold-blooded animals illustrate 

 practically all the facts which can be shown by the muscles of warm-blooded 

 animals and are therefore most advantageously used. 



1. The Muscle-Nerve Preparation. The classical muscle-nerve prep- 

 aration is the gastrocnemius muscle and the sciatic nerve. Prepare it 

 as follows: Kill the frog by pithing. This is done by grasping the frog 

 firmly in one hand and with the other making a cut with a blunt scalpel 

 through the cranium just over the medulla, turning the scalpel so as completely 

 to destroy the medulla. Now take a slender knitting needle, quickly run it 

 up into the cranial cavity to destroy the brain, and down the spinal canal to 

 destroy the cord. After a brief spasmodic contraction of the muscles of 

 practically the entire body, the frog remains limp and motionless. In making 

 the muscle-nerve preparation it is better to isolate the tendon first, then the 

 nerve, and finally the femur. The nerve should be prepared as long as possi- 

 ble and should not be allowed to come in contact with the skin. If the prep- 

 aration is to be used in a moist chamber, the skin should be entirely re- 

 moved; if it is to be used in the open air, the skin should be left on. Use 

 care not to stretch the nerve, and protect it from evaporation. 



2. The Irritability of Nerve. Prepare a muscle nerve with its skin 

 on and do not cut away the foot. Mount it by inserting the femur in a 

 muscle clamp, letting the leg extend vertically upward, and the foot hang over. 

 The nerve should lie along the exposed moist femur, one end being slightly 

 free. Stimulate the nerve in the following ways: 



a. Electrical Stimuli. Apply the electrodes from the secondary coil of an 

 induction apparatus to the tip of the nerve. When an induction current of 

 sufficient strength is produced, the muscle to which the nerve is attached will 

 give contractions, thus moving the foot. Notice that contractions occur with 

 both make and break induction. Apply the electrodes from the two poles of a 



