664 DE JAMES W. DAWSON ON 



nervous disorders has long been recognised, and also the role ascribed to the 

 secretions of the protective organs of the body — amongst which must now be 

 enrolled the choroid plexus — in neutralising the products of auto-intoxication. A 

 defective function of these organs will cause an accumulation of such toxins in the 

 body, which will immediately react on the nervous system. Orr, has shown how 

 such a primary intoxication may so lower the resisting power that micro-organisms 

 and their toxins may gain access to the blood-stream. 



Unless we admit, however, that such substances circulating in the blood can pass 

 from the capillaries, how can we explain the action of poisons on the nervous 

 system ? Williamson attributes considerable importance to the cell walls of the 

 capillaries and lymphatics of the central nervous system in reference to the pathology 

 of disseminated sclerosis. He believes that the cells of the capillary walls act as 

 true secreting cells, and when they are stimulated there is an increased flow of 

 lymph into the surrounding tissue. Certain substances, such as toxins produced by 

 micro-organisms, have the power of stimulating the endothelial walls, and as the 

 endothelial walls of the central nervous system of capillaries and lymphatics are 

 extremely delicate and active, the lymph flow is great. Numerous writers suggest 

 that the toxins produce an unrecognisable injury of the vessel wall by which it 

 becomes more permeable, and thus allows of the increased transudation of the lymph. 

 Others think it possible that a transient paralytic dilatation of the vessels permits 

 an exudation, which in other conditions does not pass through the vessel wall or is 

 arrested by the glia filter. The conditions of the cerebral circulation are so little 

 understood, and the vaso-motor mechanism so complicated, that such an irregular and 

 localised vaso-motor action may be quite possible. The presence of large areas of 

 demyelination, such as those seen in Case II, in which every level of the cord showed 

 an almost complete transection, gave the impression, however, that such an extensive 

 demyelination is preceded by acute vascular dilatation, and that the tissues are 

 flooded with toxic lymph which has caused a rapid solution of the myelin. The 

 dilated vessels found in all the " early " areas might also argue in favour of a 

 persistent paralytic dilatation from want of vascular tone in the area. 



None of these suggestions explain why certain areas are chosen while adjoining 

 areas of distribution are, at least primarily, unaffected, and it may be that its causa- 

 tion has appeared unnecessarily mysterious and that it is quite analogous to the 

 irregular distribution of other processes, e.g. the haphazard distribution of areas in 

 experimental toxic myelitis or the atheromatous patches on vessel walls. It cannot 

 be supposed that the tissues are in a state of proportionate equilibrium or equal 

 resistance, and that there are not varying degrees of oscillation and pressure and 

 permeability in the vessels. The filtration from the vessels, including whatever part 

 secretory processes may play in the passage of the lymph through the vessel walls, 

 may thus be related to alterations, the nature of which are as yet little understood, 

 but which have a place in the normal mechanism of the body. 



