THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 525 



nervous system, and, further, its relation to the different processes, e.g. diffuse 

 cerebro-spinal syphilis and diffuse arterio-sclerosis, which have as their terminal 

 product a sclerosed area. 



In addition to its unexplained cause, nature, and origin, numerous other problems 

 are met with in the study of disseminated sclerosis. A few of these falling within 

 the scope of this paper, which is primarily concerned with histological data and 

 those questions on which the anatomical picture may throw any light, may now 

 be mentioned. 



Disseminated sclerosis has been attributed to a variety of causes, some of which 

 must be considered later, but, as has been stated previously, the etiology remains 

 unexplained. A study of the cerebro-spinal fluid in disseminated sclerosis has as 

 yet thrown little light on the disease, but investigations along this line have not 

 been extensive. No culture has been obtained from the fluid, and such organisms 

 as have been found in brain and cord sections must be regarded as having an 

 accidental and not a causal relation to the disease. In the absence of any specific 

 organism the morbid changes have been attributed to the action of a toxin. This 

 hypothetical toxin has not been isolated, but it is suggested that it forms either in 

 the body, possibly in the course of an infective disease, or is brought there from 

 outside of it. For the distribution of this infective agent we have three paths : 

 the blood-vessels, the lymph-vessels, and the central canal of the spinal cord. In 

 view of the importance of the lymphatics of the central nervous system in the 

 distribution of infective agents, and the distinction, emphasised in numerous recent 

 works, between hsematogenous and lymphogenous infection of the central nervous 

 system, the histological data which give any aid in understanding this problem of 

 the path of infection will be considered. Amongst the further questions raised by 

 this consideration will be the following : why and how the toxin becomes circum- 

 scribed, and why, if it is carried by the blood-channel, it does not spread diffusely but 

 should act arbitrarily on detached smaller blood-vessels or a portion of the distribution 

 of such a blood-vessel. 



Further, clinically, the course of the disease is marked by remissions and exacerba- 

 tions, and histologically we find in nearly every case chronic areas side by side with 

 areas of a more acute process. Two questions arise : what relation have these more 

 recent areas to the original pathological process ; and, if related, is it that the 

 injurious agent has remained in the body for years or is re-formed there, or is it that 

 the original "noxa" lowered the vitality of certain portions of the nervous tissues, 

 so that, later, other exciting factors overturned the balance of repair and waste and, 

 in Weigert's sense (Wegfall von Wachstumhindernissen), disturbed the equilibrium 

 between parenchyma and supporting tissue and removed the normal controlling 

 influence which one tissue element of a complex structure normally exercises upon 

 the other tissue elements ? 



Finally, in this connection must be mentioned one striking characteristic of the 

 TRANS. ROY. SOC. EDIN., VOL. L, PART III (NO. 18). 75 



