588 PHYSIOLOGY OF THE NERVE CELL AND THE SPINAL CORD 



Goltz has made the following observations on dogs with the spinal cord cut 

 between the thoracic and lumbar regions. Erection of the penis was induced 

 by mechanical stimulation either of the penis itself or of the hypogastrium, by 

 pressure upon the bladder, and by excessive fullness of the bladder and of the 

 rectum. The bladder was emptied in perfectly normal fashion as the result of 

 mechanical stimulation of the anus. Rhythmical contractions of the anal sphinc- 

 ter, which could be inhibited by stimulating the sciatic, were induced by insert- 

 ing a finger into the rectum. Contractions of the uterus and vagina were obtained 

 by stimulating the sciatic. 



In the cat the center for micturition is located between the second and 

 fifth lumbar nerves ; that for the anal sphincter between the sixth and seventh 

 lumbar. In man the center for the bladder is said to lie at the extreme end of 

 the spinal cord near the points where the third and fourth sacral nerves make 

 their exit. 



The spinal cord also contains centers for the secretion of sweat. When 

 the spinal cord of a cat is severed below the medulla and the animal is then 

 asphyxiated, sweat appears in from two to three minutes. The same is true 

 also after cutting at the level of the ninth thoracic vertebra. 



The vasomotor and respiratory nerve centers occurring in the spinal cord 

 have already been considered at pages 238 and 325 respectively. 



Finally,, mention should be made again of the cilio-spinal center (page 

 529) discovered by Budge. This center is of special interest because, although 

 situated in the cord, it presides over an organ in the head. 



10. CONDUCTING PATHWAYS IN THE SPINAL CORD 



A. ELECTRICAL STIMULATION OF THE CORD 



Before we take up the subject proper, we must dispose of one question 

 which has been very actively discussed in its time, namely, whether or not 

 the efferent fibers in the cord are capable of being stimulated directly by 

 electricity. All authors agree that muscular contractions can be produced 

 abundantly enough by electrical stimulation of the cord; but it has been 

 claimed by some that these contractions either were caused by direct stimu- 

 lation of the root fibers or that they were reflexes discharged by stimulation 

 of the posterior columns and of the afferent fibers contained in them. 



Biedermann, however, among others, has shown that the efferent pathways 

 can actually be stimulated directly. He proceeded in the following manner. 

 The spinal cord of a frog was first split by a frontal section into dorsal and 

 ventral halves. Since the cord had also been cut transversely farther up, 

 there was found in it, as usual, a descending demarcation current (cf. page 

 48) which increased its excitability for a current in the same direction 

 i. e., for a current whose cathode coincided with that of the demarcation 

 current. Now it was shown that the ventral half of the cord was excitable 

 at its upper end for descending induction currents, while a considerably 

 stronger current was necessary to evoke a muscular contraction from a point 

 ferther down. That is, the current already traversing the cord on account 

 of the injury was reenforced to a sufficient extent by a weak induction shock 

 applied where the current of injury was stronger, and by a strong induction 



