Meyer, Data of Modem Neurology. 305 



far as our symptomatological diagnosis goes, if we miss com- 

 pletely the segmental symptoms. 



All this shows an important rule on which H. Jackson in- 

 sists strongly, namely that it is impossible to say from the char- 

 acter of the symptoms, in which place of one neurone or sys- 

 tem of neurones the lesion is located. The symptoms give 

 evidence that the neurone is deranged in its function ; whether 

 in the dendrites or the cell-body, or the fiber or the final arbor- 

 ization, cannot be said from the symptom but merely from 

 association with other symptoms referable to other neurones or 

 mechanisms. Returning to the instance of the lateral sclerosis, 

 we would say that the absence of all symptoms which would 

 refer to some other neural system, limits us to the disease of 

 the cerebral efferent system and the limitation of the symptoms 

 to the legs makes us expect that only the pyramidal system be- 

 low the brachial segments is affected. If the process were one- 

 sided and involving the arm, it might be impossible to differen- 

 tiate a simple degeneration of fibers from the effects of a slowly 

 growing tumor. The writer has lately seen a patient in whom 

 the assumption of such a tumor becomes more and more im- 

 probable on account of the long duration (six years), slow de- 

 velopment of the hemiparesis and beginning affection of the 

 opposite side. Here it is empiricism that decides ; not the 

 symptom of the neurone-complex. 



This leads us over to the diffuse diseases which may be 

 called diseases of certain levels, following H. Jackson's nomen- 

 clature. There are certain etiological and pathological entities 

 which are limited in a peculiar manner to certain types of neu- 

 rones. Not all the cells of one type are affected (just as in the 

 experiments), nor are all the segments of the body equally apt 

 to be involved. Thus, to pick out a classical instance, locomo- 

 tor ataxia consists of a lesion largely of the intra-axial (central) 

 branches of the segmental afferent neurones, those elements 

 which are drawn in blue in our chart. Other cell-types, except 

 perhaps the intersegmental association-elements of the posterior 

 horns, are not regularly and systematically enough involved t6 

 command attention clinically. Now we know that this most 



