300 DISEASES OF THE SPINAL MARROW AN D ITS MEMBRANES. 



canal, had penetrated ii.to the canal, after destroying the vertebrae or 

 their processes. 



Tumors in the spinal canal interrupt the communication between 

 the brain and peripheral nerves; hence they cause paraplegia and 

 anaesthesia of the lower part of the body. According as they simply 

 induce atrophy of the spinal medulla by pressure, or cause inflamma- 

 tion of it by the irritation of the parts about them, the paraplegia and 

 anaesthesia are preceded by moderate or by very severe symptoms of 

 irritation. Of course, the seat of the growth modifies the extent of 

 the symptoms. The fact that, in tumors, there is usually less pain in 

 the back, but more peripheral neuralgia preceding the paralysis, arid 

 that the paralysis often did not begin at the same time on both sides, 

 but gradually extended from one side to the other, is not absolutely 

 decisive in the differential diagnosis between tumors of the spinal me- 

 dulla and chronic myelitis. We can only make an absolute diagnosis 

 in those cases where the cancer extends from the spinal marrow out* 

 ward. The development of carcinoma, tubercles, or parasites in other 

 organs, at least justifies the suspicion of a similar disease in the spinal 

 canal being the cause of a slowly-progressing paraplegia. Treatment 

 is entirely powerless against all tumors of the spinal medulla. 



CHAPTEK VI. 



HYDROEHACHIS CONGENITA SPINA BIFIDA. 



HYDRORHACHIS congenita is divided into internal and external. 

 The former depends on a collection of serum in the dilated foetal cen- 

 tral canal. It causes atrophy or entire destruction of the spinal me- 

 dulla (amyelia) by pressure, or else splits it more or less completely. 

 Hydrorhachis externa consists in an abnormal collection of water in 

 the subarachnoid space. In both forms the vertebral canal may eithei 

 remain closed (hydrorhachis incolumis), or there is, at the same time, 

 a more or less extensive opening of the canal (hydrorhachis congenita 

 dehiscens). 



In spina bifida we find a sac filled with serum, and covered by the 

 spinal membranes on the spinal column, which communicates with the 

 spinal canal, as a result of rudimentary formation of one or several 

 vertebral processes. Such tumors are usually located in the sacral 01 

 lumbar regions, more rarely in the cervical or dorsal. Their size varies 

 from that of a walnut to a child's head. The skin covering them i? 

 sometimes normal, sometimes thinned ; occasionally, at the summit, it 

 has entirely disappeared; then the sac is exposed, the place appears 

 excoriated, and is occasionally covered with pus and granulations. 



