418 ADVANCED PHYSIOLOGY 



frog. If electrodes are placed on the exposed anterior end of the cord, 

 and a stimulus given from a battery current, or from an induction coil, 

 the effect on the whole posterior part of the body will prove that the cord 

 is the conductor of the shock. The above method is the neatest ; but 

 essentially the same result is obtained by probing the exposed cord with 

 a needle. 



Page 305. Spinal nerves can be easily shown by removing the organs 

 in the body cavity of a frog, after which the spinal nerves, including the 

 brachial and lumbar plexuses, show without further dissection. Their 

 number is less than in man, being ten only ; it will also be easy to notice 

 that two go to the arm (fore-foot) and are called the brachial plexus. 

 Four pass to the hind leg, and together are called the sciatic plexus. The 

 same terms are used in human anatomy. 



Page 307. The features of a nerve fiber as described here can be made 

 out by separating a spinal nerve of a frog into its component fibers, and 

 mounting them on a slide in salt solution under the microscope. 



CHAPTER XIX 



Page 314. Simple reflexes may be shown upon a frog whose head has 

 been removed or whose brain is destroyed. The latter method is neater, 

 while the former more evidently shows that the brain is absent. Suspend 

 the frog so that its body hangs downward, and then gently pinch the toe 

 or dip it into weak hydrochloric acid. 



Touch a minute spot on the flank with strong acid and note that the 

 hind leg will scratch it even with brain lacking. This well illustrates a 

 spinal reflex. 



Page 324. The main components of the sympathetic system of 

 nerves in a large frog show quite clearly as soon as the digestive tract and 

 reproductive organs are carefully removed. Do not tear out the mesen- 

 teries or the sympathetic chain will probably be ruined. It is delicate 

 but appears lying parallel to the back-bone, some of the way against it. 

 The sympathetic system can be better shown in a cat if dissected by a 

 person knowing the anatomy well. 



CHAPTER XXI 



Page 340. The parts of the eye mentioned in the next few paragraphs 

 can be best shown in a model : the external muscles are generally shown 

 on the head of a manikin. 



Have pupils note how rapidly the muscles closing the eyes operate; 

 only about .05 of a second is required to close the lid. 



