868 THE SPINAL CORD. 



Tiirck first showed, in the frog, that it is demonstrable behind a total 

 transection as well as after a partial lesion. I have seen it extremely marked 

 in the dog after high spinal complete transection, e.g. in the brachial region. 

 The lightest touch on the skin of the shoulders or arms appeared to cause 

 acute sensation, though there was no redness or sign of vascular disturbance 

 in the skin. It has been suggested that the hyperaesthesia is due to 

 vasomotor disturbance ; but Foster l points out that irritation or paralysis of 

 the cervical sympathetic is not shown to cause any disturbance of sensation in 

 the skin of the ear, and a one-sided hypersemia of the cord itself is difficult to 

 postulate. It has been noted immediately after the establishment of the 

 lesion, which is against its being of inflammatory origin ; it does certainly 

 usually become more marked a few days after the establishment of the lesion. 

 Its persistence for many weeks excludes its explanation by " injury 

 currents" set up in the spinal nerve fibres. WoroschilofPs seems the best 

 explanation, namely, the removal of tonic inhibitory influences ; although to 

 state this is, in our present knowledge, to say little definite. In the cat, 

 immediately after high spinal transection, e.g. from the first cervical level as 

 far back as the sixth, a peculiar condition is often observable in front of 

 the section, e.g. in the sensorial field of the trigeminus. A single touch on 

 the snout elicits vigorous licking of the spot touched ; the mere approach of 

 the warm can used to protect the animal from cold evokes screwing-up of the 

 eyes and mouth ; salivation is often profuse ; a touch on the vibrissse produces 

 exaggerated facial movement; there often seems to be some photophobia. 

 But in the dog and monkey, although there are indications of a somewhat 

 similar condition, they are but slight. Perhaps related to the Fodera hyper- 

 sesthesia is that heightened sensitivity, which a field of skin, supplied by a 

 portion of an afferent spinal root, exhibits after severance of the rest of the 

 root and of adjoining roots in front of and behind it. Similarly the knee- 

 jerk (cat) is extremely brisk when the two segments to which its reflex arc 

 belongs are isolated from all the rest of the cord, by spinal transections just in 

 front and behind. This reaction recalls the observation by Brown-Sequard, 

 that after section of the dorsal columns it is the posterior face of the section 

 that is the more sensitive, and that of the two next adjacent dorsal spinal 

 roots it is the one on the posterior side of the lesion that is the more 

 excitable. Here injury currents were perhaps playing a part, for the obser- 

 vations were all made soon after the establishment of the lesion. But it has 

 been shown that a semisection carried out on the same side a few segments 

 further back reduces the hypersesthetic symptoms, Vulpian 2 says actually to 

 in excitability, excito-motility as well as sentience suffering extinction. 



TONIC FUNCTIONS OF THE CORD. 



Among the reflex functions of the spinal cord are some that, on 

 account of the comparatively prolonged and steady character of their 

 centrifugal effect upon the extrinsic tissues, are described under the term 

 " neural tonus." It is in certain parts of the musculature that this tonus 

 lies best open to examination. The sphincters of the anus, urinary bladder, 

 and larynx, by a continued degree of steady unwilled contraction, guard 

 their respective orifices. Destruction of the spinal cord abolishes their 

 action for a time, but in the instances of the anal and vesical sphincters 

 an efficient amount of tonic contraction is eventually regained. The 

 sphincter muscles can, like other muscles, be excited reflexly through 

 the cord to that status of decreased extension and increased tension 

 which constitutes tetanic or voluntary contraction. But in addition 

 to these intercurrent relatively brief contractions, they exhibit under 



1 " Text-Book of Physiology," 1891, pt. 3. 2 Compt. rend. Soc. de HoL, Paris, 1855. 



