680 DR JAMES W. DAWSON ON 



histological study it has been pointed out that it is not a question of one central 

 vessel, a portion of the longitudinal course of which is affected, but rather of a 

 blood-vessel stem with its terminal branches or a division of its branches. It is 

 probable that the circulating toxin escapes from the capillaries and transition vessels 

 in the sense that the area of supply of the ramifications is affected. It has been 

 suggested that the toxin may have a chemiotactic influence on certain portions of 

 brain tissue, but it is difficult to conceive of such an irregularly and widely 

 distributed chemiotaxis unrelated to definite functional nuclei or fibre-systems. 

 The toxin may, however, conceivably select certain areas of blood supply, for it is 

 known experimentally that certain substances can influence the blood supply of 

 regional parts of the brain, and Meynert has suggested that this may be the 

 explanation of the maniac depressive psychoses, which he looks upon as neuroses 

 of the vaso-motor system limited to certain cerebral areas. The recent experiments 

 of Orr and Rows also point to the possibility of a localised affection of the vaso- 

 motor system due to the action of toxins on the sympathetic nerves. In the 

 present state of our knowledge, as it is impossible to determine the final causal 

 agent, it is equally impossible to determine the factor which allows of its diffusion 

 through certain terminal areas of the ramification of a blood-vessel. 



(v) It is suggested, however, that the restriction and distribution of the 

 pathological process is in some way related to the selective action of the toxin on 

 certain areas of the blood supply, or that unknown factors determine an irregularly 

 distributed paralytic dilatation, with an increased filtration through the vessel walls. 



It is, further, necessary to explain not only the presence of this morbid agent in 

 the blood-vessels, the restriction and distribution of its effect, but also its continued 

 presence in the body through a series of years, during which its action is apparently 

 exhausted, remains quiescent, and again breaks out. Clinically the remissions and 

 relapses are the outcome of this peculiar action, and anatomically it finds expression 

 in the areas in different stages of development in the same cases. Allowing that it 

 is microbial in origin, we may find an analogy in cerebro-spinal syphilis, in which 

 there are also the same exacerbations and remissions. If we admit, rather, its toxic 

 origin, the closest analogy is probably found in pernicious anaemia, where it is 

 thought likely that both the haemolysis and the cord changes are due to the same 

 toxin. The source of the toxin is here also uncertain, but the fact that gastro- 

 intestinal disturbances are so common in this disease lends support to the view that 

 it is of intestinal origin, and that its intermittent evolution or its insufficient 

 elimination lead to the remissions. Such analogies can again not be final, and in 

 the latter case the parallel breaks down from its incompleteness. There is no known 

 association of disseminated sclerosis with any changes in the gastro-intestinal tract 

 or elsewhere : the connection, if any, with glands of internal secretion has never 

 been worked out : the general metabolic changes occurring in the body have not been 



