THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 673 



VI. 



CONCLUSION. 



The three divisions of this study have now been completed : in the first an 

 analysis and classification were given of the more important writings on this 

 subject ; in the second part the essential features of the histological process were 

 set forth and an endeavour was made to avoid the needless* repetition of examples 

 and details by the selection of such examples as were necessary to a complete view 

 of the subject ; and, finally, it was attempted to bring out in order the nature of 

 the questions that come into consideration in a study of the pathological process 

 underlying disseminated sclerosis. In the critical discussion which this involved 

 it was clear that no general and complete interpretation of the subject could be 

 given, and that imperfectly known factors had to be suggested for the solution 

 of several of the problems. It may have seemed, on the one hand, that difficulties 

 have been suggested where everything was clear : if this be so it is because it was 

 difficult, sufficiently clearly, to define the real point at issue ; on the other hand, 

 in one or two cases, it has been noted that the difficulties are there, undeniably, but 

 that their importance may easily be overestimated. The tentative nature, therefore, 

 of the attempted explanations on many points, and the fact that no uniform con- 

 ception of the process can be offered, make it difficult, in these closing pages, to 

 summarise the foregoing study. Nevertheless, it is customary and desirable to 

 formulate certain conclusions, and the extent both of the histological examination and 

 the critical examination of the available literature seems to justify such an attempt. 

 The first group of these conclusions is related to those problems which are far from 

 being completely solved ; the second group rests on more definite histological data. 



As the initial conclusion, that related to the nature of the pathological process 

 may be selected. Its sequence, as it has presented itself to me in the normal 

 evolution of an area of sclerosis, is distinguished by several stages, which may be 

 briefly stated in terms of their dominant feature : (l) a commencing degeneration 

 of the myelin sheath and a simultaneous reaction of the glia in the immediately 

 peri-vascular tissue ; (2) an increasing glia cell proliferation and a commencing fat 

 granule cell formation; (3) the stage of so-called "fat granule cell myelitis"; (4) a 

 commencing glia fibril formation ; (5) an advancing and (6) a complete sclerosis. 

 It is possible, and the possibility has been allowed for in the interpretation, that 

 complications, e.g. septic fever, extreme decubitus, etc., may modify the presenta- 

 tion of the picture at any stage. The histological study has given overwhelming 

 evidence that the great majority of the areas in these cases, both in the brain and 

 spinal cord, have arisen on the basis of this evolution through a stage of fat granule 

 cell formation. On the ground, therefore, (l) of the nature of this evolution, 



