1.) That a large proportion of patients suffering from disseminated sclerosis give a history of exposure to damp, especially of the hands and feet. 2.) That a large proportion give also a history of association with rats at home or at work. 3.) That a study of the occupation of those dying of the disease in England and ';ales in 1925 shows a heavy incidence in those occupations which would expose the worker to the above etiological factors. 4.) That the geographical distribution of cases in isnerica, and to a lesser extent in London round inland waters is in keeping with the clinical and occupational findings. 5.) That bacteriological opinion suggests a leptospira related to leptospira icterohaemorrhagiae as the casual organism of disseminated sclerosis, and that there is a strong probability that these organisms have an ineffective and a non-ineffective phase. 6.) That in general the association of rats, 'damp, and disseminated sclerosis is too frequent to be dismissed as merely accidental) without further investigation.