654 DR JAMES W. DAWSON ON 



conceptions of disease do not admit of primary importance being attached to the 

 influence of cold, injury, strain, and emotion in the production of diseases of the 

 nervous system, but such influences, recent or remote, are repeatedly brought into 

 relation to the onset of such diseases. As a rule we cannot go beyond the " post hoc 

 ergo propter hoc " argument, for there are no other data available, yet it is necessary 

 to consider briefly whether the histological data throw any light upon the mode of 

 action of such influences, which are at least admitted to bring about a lowered 

 resistance of the nervous system to the causal agent. 



(a) Trauma. — Slight degrees of dystocic lesions of the infantile spinal cord 

 may lead frequently to slight degrees of haemorrhage, and it is thought not 

 improbable that these may be the basis of the diseases of the spinal cord which are 

 related to the formation of multiple areas of sclerosis, or to the formation of cavities 

 and later syringomyelia. Mendel is one of the principal advocates of the traumatic 

 etiology of disseminated sclerosis. He believes that as a result of the trauma an 

 impulse of movement is transmitted to the cerebro-spinal fluid, that this leads to 

 pressure effects in the most delicate channels of both brain and spinal cord, and that 

 through these alterations of pressure there may occur minute ruptures (of capillaries) 

 and haemorrhages. From the assumption that small haemorrhages are sufficient to 

 evoke symptoms of disease, there justifiably follows, therefore, the view that in the 

 case of cerebral and spinal " commotio," intra-medullary haemorrhages are responsible 

 for the symptoms. That the symptoms frequently pass away rapidly must be 

 ascribed to a rapid resorption of the poured out blood, but Schmaus argues from the 

 fact that, since permanent disturbances frequently remain after shock, processes of 

 degeneration in the nerve elements, which are beyond our present methods of 

 recognition, have occurred. Hence his expression " molecular alteration of the 

 nerve elements." The slighter degrees, he thinks, lead to transient symptoms, the 

 severer to focal areas of degeneration, which thus have their rise in a molecular 

 alteration resulting from " commotio." 



The assumption of a molecular alteration of the nerve elements is hypothetical, 

 since it does not rest on demonstrated microscopic findings at the time, but in the 

 opinion of many writers intra-medullary haemorrhages or outpourings of lymph into 

 the tissue, of traumatic origin, may be followed by swelling and degeneration which 

 lay the foundation of a " locus minoris resistentiae " for toxic infective agents. It is 

 also thought possible that in such damaged areas, still capable of functioning, the 

 damage may be completed by any other factors which lower the resistance of the 

 tissue. In relation to multiple haemorrhages, it is relevant to mention the view put 

 forward by Taylor and others, that at least a portion of the spinal cord degeneration 

 found in some cases of pernicious anaemia is due to primary focal degenerations 

 caused by haemorrhages similar to those which occur in the retina and elsewhere in 

 this disease. In the literature on disseminated sclerosis there are several cases 

 reported in which the association between trauma and the onset of the disease was 



