678 PHYSIOLOGY. 



which conduct muscle-sense to the cerebellum. Tactile and muscular 

 sensations are abolished by locomotor ataxia. 



One-sided section of the posterior and lateral columns causes: 

 (a) suppression of skin sensations, or anaesthesia, in the whole half 

 of the body innervated by nerves which enter the cord below the side 

 of section; (b) loss of motion on side of section. There is very fre- 

 quently observed on the side of hemisection a zone of hyperaesthesia ; 

 this is due either to removal of inhibition on that side or inflamma- 

 tory irritation of the central extremity of the cut cord. 



It has been shown by Woroschiloif in Ludwig's laboratory that 

 the lateral columns are a pathway for sensory impulses. I have 

 shown with Dr. Robert M. Smith similar results in a series of sections 

 of the lumbar part of the spinal cord. 



Section of the posterior and lateral columns does not exercise 

 any influence upon sensibility to pain and temperature. But this 

 is not the case when the gray matter is cut; so that it must be 

 inferred that these impulses ascend through the gray substance to 

 the brain. 



Syringomyelia is the term applied to that condition when there 

 is complete abolition of the conduction of pain and temperature. It 

 is due to vacuolation of the gray matter of the cord. 



FIBERS FROM THE CENTERS OF THE MEDULLA OBLONGATA. The 

 vasomotor nerves, which come from a center seated in the medulla 

 oblongata, run clown the lateral column to penetrate the gray sub- 

 stance and anterior roots. Hence, section of the lateral columns 

 produces a dilatation of the arterioles innervated by vasoconstrictors, 

 which leave the cord below the point of section. 



The nerves leaving the respiratory center also run through the 

 lateral columns and enter the gray substance, to communicate with 

 it and leave by the anterior roots, 



In the middle third of the lateral columns I have found running 

 both sweat and inhibitory fibers. Both sets of fibers, I have discovered,, 

 decussate : the former in the spinal cord, the latter in the medulla. 



Skin Reflexes. The most important skin reflexes in man are : 



1. THE PLANTAR REFLEX, which is caused by tickling the sole 

 of the foot. The involved center lies in the lumbar cord. 



2. THE CREMASTERIC REFLEX. If the skin of the upper and 

 inner surface of the thigh in man be excited, the corresponding 

 testicle will be seen suddenly to rise by contraction of the cremaster 

 muscle. Its center lies between the first and second lumbar nerves. 



