LESSON L 



EXCRETION (Concluded) 

 THE INNERVATION OF THE BLADDER. PILOMOTOR REACTIONS 



1. The Function of the Hypogastric Nerves. Anesthetize a cat and 

 maintain the anesthesia throughout the following experiments: Per- 

 form tracheotomy. Open the abdominal cavity by a median incision 

 in the linea alba. Identify the urinary bladder, and raise its fundus 

 sufficiently to expose the fatty tissue investing its cervical portion. 

 By careful dissection isolate the nerve-fibers which ascend from here to 

 the fundus. Place them in shielded electrodes, and arrange the elec- 

 tric apparatus for stimulation with a tetanizing current of medium 

 strength. 



Insert a small hook in the top of the fundus of the bladder and 

 connect it by means of a thread with the end of a writing lever (suspen- 

 sion method). Counterpoise the lever so as to place the musculature 

 of the bladder under a certain tension. Place cotton moistened with 

 warm saline solution around the base of the bladder to protect the 

 abdominal organs against evaporation and thermal influences. Allow 

 the drum to revolve at a slow rate and stimulate the hypogastric fibers 

 until a contraction of moderate height has been obtained. 



Cut one nerve and stimulate the central end of this nerve. Note 

 that the bladder is now made to contract reflexly through the hypo- 

 gastric center and intact nerve on the opposite side. 



2. Pilomotor Effects. Unite the margins of the wound in the 

 abdomen by a few sutures. Make a median incision through the skin 

 covering the base of the tail and posterior extent of the vertebral 

 column. Reflect the muscles. Clip away the spinal processes and 

 adjoining laminae of several vertebrae near the base of the tail. Apply 

 a cotton tampon until the bleeding has stopped. Incise the dura 

 mater and identify the chorda equinae. Isolate several of its constituent 

 nerve-fibers close to the base of the tail and place them in loose liga- 

 tures. Smooth the hairs of the tail' and place the latter upon a sheet 

 of white paper. Note its volume. Stimulate the nerve-fibers just 

 isolated successively with a weak tetanizing current, until one is found 

 which causes an erection of the hairs of the tail. Again smooth the 

 tail and repeat this experiment. Explain the mechanism by which 

 hairs are erected. Kill the animal by an overdose of ether. Repeat 

 the stimulation of these pilomotor fibers after an interval of several 

 minutes. Note that this mechanism remains effective for some time 

 after death. 



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