PATHOLOGY OF SENSIBILITY 29 



All the sensory stimuli, caught in the periphery of the 

 body, are sent to the spinal cord and to the brain. For a 

 better understanding of the matter we shall limit ourselves 

 to the spinal cord. The same line of thought may be fol- 

 lowed concerning sensibility of the head, which is conveyed 

 to the oblongata by the trigeminal nerve. 



Thus the stimuli for touch, pain, temperature and the 

 proprioceptive sensibility reach the intervertebral ganglions 

 and then proceed through the posterior roots. Here in 

 America Ranson found after careful investigations that 

 there are many unmedullated fibres in the posterior roots. 

 He believes that these conduct the protopathic sensibility 

 of Head. 



What happens when all these stimuli are brought by the 

 posterior roots into the spinal cord? In the conception of 

 Head and others a new grouping of the sensory impulses 

 arises as soon as they reach the central nervous system. 

 One group reaches the gray substance on the same side and 

 here the first sensory neuron ends. A new neuron issues in 

 the cells of the posterior horns. It mostly crosses and pro- 

 ceeds upwards in the antero-lateral part of the spinal cord. 

 The other group avoids the gray substance and ascends 

 in the posterior column on the same side. It ends in the 

 nuclei of Goll and Burdach, which lie at the upper border of 

 the spinal cord. Here it is that the second sensory neuron 

 begins, crosses in the oblongata and ascends to the optic 

 thalamus. 



The investigations of Petren, Fabritius, Head, van Valken^ 

 burg and others have made us pretty well acquainted with 

 the physiological significance of these two systems. The 

 sensory pathways in the posterior columns of the spinal 

 cord conduct stimuli of deep sensibility and a part of the 

 tactile impulses. The other system comprises the stimuli 

 for pain, heat and cold and the remaining part of tactile 

 sensibility. Many investigators consider the sensibility 

 of the posterior columns as a higher form. It enables us to 



