THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 669 



seminated encephalomyelitis, but, in spite of the seeming inconstancy of the 

 symptoms and the irregular incidence in the position of the areas, it seems justifiable 

 to regard disseminated sclerosis as an inflammatory process with a subacute onset 

 and slow progressive course — often distinguished by remissions and acute or sub- 

 acute relapses which depend upon the development of new areas, and to regard the 

 final cause as a true specific " noxa," which may be either a metabolic disturbance 

 or a special infective stimulus. 



4. Route of Conveyance of the Causal Agent to the Tissues. 



Writers admit two paths of infection of the central nervous system — the one, 

 which has been looked on as the more constant, — the blood stream, and the other 

 the lymph stream. The possibility of lymphogenous infection of the nervous 

 system has received much attention since experimental evidence was established 

 in favour of the spread of rabies and tetanus by the lymph channels of the nerves. 

 Its increasing recognition in this country is largely due to the work of Orr and 

 Eows, who have taken as the principle of their research the fact, demonstrated by 

 numerous experiments with organisms and coloured fluids, that the lymph stream 

 in peripheral nerves is an ascending one and capable of conveying infection to the 

 central nervous system. The main current of this ascending lymph stream is said 

 to lie in the inner meshes of the peri-neural sheaths, and when it reaches the cord, 

 chiefly by the posterior roots, it for the most part passes along the entering posterior 

 nerve roots into the substance of the cord, and the remainder is distributed in the 

 inner meshes of the arachnoid around the whole surface of the cord. The lymphatic 

 path within the cord has, in the main, an outward direction, as is demonstrated by 

 the presence of fat granule cells, containing the degenerated products of the nervous 

 tissue within the adventitial spaces, but the experiments of Homen, Salle, and 

 Marinesco, together with numerous histological observations, leave no doubt that 

 it admits of a current inwards: — thus admitting an invasion by cellular elements, 

 micro-organisms, and toxic substances. 



In the experiments of Orr and Eows, celloidin capsules containing a broth 

 culture of an organism were placed in contact with the sciatic nerve. The path of 

 the toxic lymph could be traced by the inflammatory reaction in the sciatic nerve, 

 posterior root ganglia, and along the spinal roots. If the capsules were placed 

 near to the spinal cord, in order to lessen the distance along which the infection 

 had to be conveyed, this reaction was evidenced within the cord substance itself, 

 and its characteristics depend entirely on the potency of the | irritant. When the 

 capsules had not burst and the tissues were attacked by toxins only, the reaction 

 was of a plasma-cell type, but when the capsules had burst and the organisms had 

 grown in the tissues, there was an intense proliferation of cells of poly blast type. 

 As the same animal was used and the same organism, the differing reaction must 

 be attributed to the difference in quantity and potency of the irritant. The reaction 



TRANS. ROY. SOC. EDIN., VOL. L, PART III (NO. 18). 93 



