666 DR JAMES W. DAWSON ON 



may be the cause of disseminated sclerosis. Before Noguchi's discovery of the 

 spirochseta pallida in the cortex, Mott and Sewell had defined these relations thus : 

 (l) the syphilitic organism is in itself the causal organism; (2) there is produced 

 within the body as the result of syphilis a toxin, and this post-syphilitic toxin is the 

 cause ; or (3) syphilis produces an impairment of the nervous system and so pre- 

 disposes it to degeneration from auto-toxins and other causes. It is in this final 

 sense we look upon Redlich's and Marburg's conception — that acute infectious 

 diseases of very varied etiology may produce once for all a specific impairment of 

 the nervous system, and so predispose it to degeneration from auto-toxins. It has 

 also been suggested that the original agent may cause, in addition to the evident 

 areas of degeneration, alterations in other portions, and that these later, not from a 

 persistence in the organism of the causal agent, but from excess of function, strain, 

 or circulatory disturbances, may degenerate. Again, that the presence of degenera- 

 tive processes in the central nervous system may suffice in themselves for the 

 production of further areas of degeneration. For either of these views there is no 

 foundation nor analogy. In the absence, therefore, of any positive evidence as to 

 the determining factor, it can only be presumed that relapses are due either to 

 the intermittent evolution of a toxin, or to an unknown organism which, in the 

 interval between a remission and a relapse, lies latent and inactive. The causation 

 of pernicious anaemia, as we have seen, is thought to be due to the similar inter- 

 mittent evolution of a toxin, and the discovery of the spirochseta pallida in the cortex 

 in general paralysis is a sufficient analogy for the latter alternative: Mott has 

 suggested that this organism may exist in a latent, granular, or intracellular form 

 in the parenchyma of the nervous system, where it cannot be reached by drugs such 

 as arsenic, mercury, and antimony. 



3. The Factors which cause a Modification in the Action of the Causal 

 Agent and the Relation of the Process to Acute and Chronic Myelitis. 



The variations in the histological picture have been ascribed by different 

 writers to two main causes : the fact that the process was observed at different 

 stages, and to the different nature of the etiological factor in individual cases. 

 Apart from such basal differences and from the variations due to the influence of 

 complications, there are modifications in the development of the process which 

 can be attributed only to the fact that its progress, assuming one common causal 

 factor, is not always typical, uniform, and progressive. 



Ainley Walker, in discussing the relative changes in the tissue elements in 

 inflamed areas, points out that stimulation and injurious irritation differ only in 

 degree, and that whatever is capable of causing injury will, if sufficiently diminished 

 in intensity, exert a stimulant action. On the other hand, stimulation, if sufficiently 

 intensified or long maintained, becomes irritation and produces injury. He further 

 points out that one and the same agency may have a different effect on different types 



