652 DR JAMES W. DAWSON ON 



at a stage when the secondary infiltration of fat granule cells and the cellular 

 reaction to their presence had occurred. 



Alongside of the vessel lesions and dependent on them, Borst, Schmaus, and 

 other writers have described disturbances of the lymph circulation. The sequence 

 of the process is a little difficult to follow, for the change may be evidenced by a 

 slight oedema and rarefaction of the tissue around a vessel with a dilatation of its 

 adventitial lymph spaces, or it may be marked by a closure of the lymph spaces and 

 a lymph stasis in the tissues from obstruction to the return flow of the lymph. 

 Borst thought that a chronic inflammatory meningitic change initiates the process, 

 leading to a closure of the epi-cerebral and epi-spinal spaces of His ; the blood-vessel 

 changes, especially around the para-central vessels, cause a closure of the adventitial 

 lymph spaces, leading to a dilatation of the peri-vascular lymph spaces, and, with 

 increased distension, the formation of cysts. As the congested lymph passes into 

 the surrounding tissue, there comes about a hyperlymphosis with the formation 

 of " Lichtungsbezirke." The obstruction to the outflow of the cerebral-spinal fluid 

 by the obliteration of the adventitial lymph spaces and the closure of the epi- 

 cerebral and epi-spinal spaces are therefore the causes of the disturbed lymph 

 circulation. The acute infection which precedes the disease is stated to give rise 

 to chronic inflammatory and proliferative processes in the meninges and vessel walls. 

 In dependence on the lymph stasis a swelling and degeneration of the nerve fibres 

 in the "Lichtungsbezirke" is brought about, and a later compensatory growth of 

 neuroglia. The present writer's views in regard to the changes in the lymphatics 

 and meninges have been stated elsewhere, and it is necessary here only to note that 

 in these observations, in uncomplicated cases, no alteration in the meninges to which 

 any significance could be attached could be found. The chronic inflammation in the 

 vessel walls, with a closure of the lymph spaces, is to be regarded as entirely a late 

 change, so that while I agree with Borst that the fundamental basis of the process 

 underlying disseminated sclerosis may probably be a flooding of the tissues with 

 toxic lymph, I disagree with him regarding the mechanism by which this is 

 brought about in the early stages. In late stages the condensed vessel wall, with 

 adhesion of the adventitial spaces, on its side may contribute to the production of 

 a vicious circle in which hyperlymphosis plays a part. 



It is thus seen that I am in more or less disagreement with all the views related 

 to the primary nature of the vascular lesions. 



(3) The Etiological Factors. 

 In turning now from the nature and origin of the process to its determining cause, 

 we find that there is no positive knowledge of the nature of the agent causing this 

 disease. The etiological factors postulated may be discussed under two groups : 

 developmental and external. 



