636 DR JAMES W. DAWSON ON 



result of the development of patches in the optic tracts and chiasma. Later the 

 areas in the spinal cord became still more extensive, and the effects of a lower 

 neurone lesion became evident, resulting in muscular wasting and emaciation. 



V. 

 PATHOGENESIS AND ETIOLOGY. 



PA OK I PAGE 



Introduction 636 2. External : 



(1) The Nature of the Pathological Process : 



1. Developmental 638 



2. Inflammatory 644 



(2) Its Origin : 



1. In the Neuroglia 646 



2. In the Nerve Elements .... 647 



3. In the Blood-vessels and Lymphatics . 649 



(3) Etiological Factors : 



1 . Developmental ...... 653 



(a) Trauma 654 



(6) Psychical Shock . . .655 



(c) Chill 655 



(d) Exogenous Intoxications . . . 655 



(e) Infection and Endogenous Intoxications 656 



(4) Mode of Action of the Causal Agent : 



1. Irregular Distribution and Circumscription 661 



2. Further Advance of the Process '. 665 



3. Modifying Factors 666 



4. Route of Conveyance to the Nervous Tissues 669 



Introduction. 



To record these observations is the chief object of this paper : the secondary, but 

 more difficult, task is to try to interpret them and to correlate the various concep- 

 tions which emerge in the process. It may be stated at the outset that no satis- 

 factory explanation of the pathological process in all its bearings has yet been put 

 forward, and that all that can be done here is roughly to estimate the factors which 

 have been at work. It has been already pointed out that different investigators have 

 given a different meaning to the same histological picture, while others, working 

 solely or largely with individual elective staining methods, have laid stress on the 

 feature of the process which that staining method rendered prominent. One 

 important group, working with glia methods, considers that all the changes are 

 subordinate to the primary glia proliferation. Another group, working with 

 medullated sheath methods, equally forcibly maintains the primary parenchymatous 

 origin of the process ; and still others, working with diffuse stains, see in the changes 

 in the blood-vessels the key to the whole process. From the histological point of 

 view, therefore, the most important problems centre round the question of the role 

 which falls to the various tissue elements in the origin of the process. From 

 a clinical point of view, on the other hand, the question of the nature of the 

 process is of more interest. 



In the introduction it was briefly noted that it was necessary to discriminate 

 between the nature of the process underlying disseminated sclerosis and its origin. 

 In its nature it is due either to developmental causes, i.e. those inherent in the 

 individual, or to inflammatory causes, i.e. those due to infections, intoxications, 

 circulatory disturbances, etc., — these two groups not being necessarily exclusive, as 

 will be pointed out later. In its origin the primary change may arise in any of the 



