LESSON XXXIV 

 THE NERVOUS SYSTEM (Continued) 



STIMULATION OF THE CEREBRUM. THE FUNCTION OF THE ROOTS 

 OF THE SPINAL CORD 



1. Cerebral Localization. Procure a pair of adjustable electrodes 

 and connect them with the secondary coil of an inductorium. Arrange 

 the electric apparatus for stimulation with a quickly interrupted cur- 

 rent. Anesthetize a cat and maintain the anesthesia throughout the 

 following experiments: Perform tracheotomy. Place the animal on 

 its side. Make a median incision through the skin covering the skull- 

 cap, and separate the edges of the temporal muscles from the bone 

 underneath. Adjust a trephine, about 1.5 cm. in diameter, to the 

 anterior area of the right parietal bone at a distance of 0.5 cm. from the 

 median line. Carefully work the trephine until it has penetrated the 

 skull. Do not press upon it heavily so as not to break through suddenly, 

 piercing the substance of the cerebrum. Remove the round plate of 

 bone with a pair of forceps. Apply dry cotton, and stop the bleeding 

 by pressing soft wax against the edge of the cut bone. Identify the 

 dura mater and its blood-vessels. 



Observe that the surface of the dura rises with every systole of the 

 heart and also during inspiration. Insert a thistle tube in the trephine 

 opening. Fill it partly with warm saline solution and connect it with a 

 recording tambour. Register these pulsations upon the smoked paper 

 of a kymograph. The cranial cavity is in this way converted into a 

 plethysmograph, registering the cardiac and respiratory changes in the 

 volume of the brain. 



Remove the thistle tube and enlarge the trephine opening by means 

 of a pair of bone forceps until the crucial area of the cerebrum has been 

 completely uncovered. Stop the bleeding by means of wax and cotton 

 tampons. Incise the dura mater, noting the escape of liquor cerebro- 

 spinalis. Reflect the dura and expose the surface of the cerebrum along 

 the crucial sulcus (fissure of Rolando). Place the animal on its right 

 side and unfasten the left fore- and hind limbs. 



Using Fig. 97 as a guide, stimulate the surface of the cerebrum in 

 the vicinity of the crucial sulcus with a weak tetanizing current. If no 

 results are obtained, increase the strength of the current gradually and 

 lessen the depth of the narcosis. Analyze the movements resulting in 

 consequence of the stimulation of these different areas. 



2. The Function of the Roots of the Spinal Cord. Close the wound 

 by means of a continuous suture. Make a median incision through the 

 skin covering the spinous processes of the lumbar vertebrae. By means 

 of forceps separate the fascia and muscle tissue from these processes. 



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