658 DR JAMES W. DAWSON ON 



conditions, must be ascribed to true acute myelitic conditions, for Pierre Marie 

 regarded the primary participation of the blood-vessels as an anatomical proof of his 

 clinical theory of the relationship. Cases of acute infective infiltrative myelitis, 

 with organisms present in the foci, have been described by Purves Stewart and 

 others, and there are also other cases in which it is impossible to state the exact 

 nature of the infection. Further, the experimental investigations of Marinesco, 

 Hoche, Homen, Salle, and others have corroborated the organismal cause of certain 

 forms of myelitis by the production of focal areas of infiltrative myelitis as a result 

 of the infection of micro-organisms. These writers believe that organisms exert 

 their action primarily upon the wall of the blood-vessel. 



The forms of myelitis have been classified by Taylor and Buzzard as infective, 

 toxic, and syphilitic. The last-named variety shows changes which we have already 

 noted as being readily recognised, and as quite distinct from the changes in dis- 

 seminated sclerosis, so that it need not be further considered. The experimental 

 work we have above referred to has shown that areas of infective and toxic myelitis 

 may be produced by a number of bacteria and bacterial toxins, and a comparison of 

 the histological changes in the two forms with those of similar conditions in man 

 gives the following as the general differential histological characteristics. In infec- 

 tive myelitis we have dilated and engorged vessels, with an excess of nuclear 

 elements in the adventitial sheath, probably derived from the proliferation of the 

 structural elements of the adventitia rather than from the blood (Taylor and 

 Buzzard). Later there is proliferation of the glia elements and changes in the nerve 

 cells and fibres, partly due to oedema and to the vascular changes, and partly to the 

 toxic products of the invading organisms. In toxic myelitis, on the other hand, the 

 changes are much less marked : the patchy areas of degeneration are unaccompanied 

 at first by any cell infiltration of the vessel-adventitia or of the tissue, and there is, 

 as a rule, marked swelling and varicosity of the axis cylinder and myelin sheath. 

 The later reactive changes in the glia depend on the intensity of the primary change. 



From the evidence of an infiltrative poliomyelitis, caused by the virus of polio- 

 myelitis ; from the recorded cases of acute infiltrative myelitis in man ; and from 

 the experimental production of infiltrative myelitis by bacterial injection into 

 animals, it is natural to assume that organismal infection is more often associated 

 with primary inflammatory (proliferative) changes in the blood-vessel walls. Taylor 

 and Buzzard, however, point out that some organisms may at one time and under 

 certain circumstances determine an infiltrative form of myelitis and at other times a 

 toxic, and that we are not fully acquainted with the laws which govern such different 

 results. It must also not be forgotten that toxins circulating in the blood or 

 lymphatics may also produce lesions first in the vessel walls ; the work of Orr and 

 Rows has definitely proved that a cellular reaction in the adventitia may be due to 

 a chronic lymphatic intoxication — the presence of numerous plasma cells in this 

 reaction is the expression probably of a chronic inflammatory process. The balance 



