Meyer, Data of Modetn Neurology'. 251 



arises because many nerve-elements are so large and spread 

 into so many types of tissues, that a great variety of lesions 

 must be considered ; ischaemic necrosis may involve tissue with 

 a cell-body, or only with a dendrite of one neurone or with the 

 fiber or its termhiation and a simple lesion to a particle of tissue 

 produces ' secondary ' reaction in the ' outlying ' part of the 

 neurone. Another general fact deserves attention. A poison 

 which is distributed by the circulation affects different elements 

 of the tissue in different manners ; and will even select different 

 parts of the cell-individuals. We know, for instance, that the 

 — final termination of fibers and the myelin sheaths show a pecu- 

 liar vulnerability to certain poisons (the metasyphilitic and the 

 diphtheritic). 



The general laws of interrelation of the chief constituents 

 of the nervous tissues have been first outlined in a classical ar- 

 ticle by Weigert. (Weigert, Centralblatt f. Pathologic, Vol. I, 

 p. 729). On the whole the following will represent the pres- 

 ent status of the problem. 



In the central nervous system there are three types of 

 constituents of the tissues : 



a. The nerve-elements proper, the highest type in the 

 hierarchy both from the point of view of functional complexity 

 and delicacy, and of difficulty of regeneration. 



b. The neuroglia, also of epiblastic origin, but being less 

 delicate and of the character of an interparenchymatous sub- 

 stance ; part of it, many of the fibrils, are even put into the 

 class of real intercellular substance (see page 129). 



c. The blood-vessels, of mesoblastic origin, like the mem- 

 branes (pia). 



I am not aware of any peculiarity of the circulatory tissue- 

 elements in the nervous system apart from the great tendency 

 towards cell-proliferations, and pass over its general architec- 

 tonic and pathological features. The claim of Hill and certain 

 English students, that the blood-vessels of the brain are devoid 

 of nerves has been invalidated by Obersteiner and I can adduce 

 preparations to the same effect. 



