526 TRANSACTIONS OF SECTION I. 



reactions of nuclear material in other parts. Permanent sites of monotonous 

 nuclear activity are formed and maintained in such places until the moment 

 when some unusually extreme condition still further limits their activity and 

 terminates their existence. It is significant, too, that this may happen when 

 the condition is not sufficiently extreme similarly to cut short the reactions of 

 other parts. 



Now the latter case is typically illustrated by reference to the nervous 

 system, which is thus seen as the site of a severely limited quality of chemical 

 activity. That it is also restricted in amount may be further emphasised by 

 reference to the relatively minute quantity of nuclear material which is present 

 in this system. Thus it is probable that if a direct comparison between the 

 cells of the nervous system and the lymphoid cells to which I have alluded 

 were possible, the essential difference found would be a difference between the 

 stability of certain chemical material in the one case, and a frequently modified 

 wealth of chemical reaction in the other ; so that of the two, the nervous system 

 would be the more comparable with the red blood corpuscle. 



Thus, if when reviewing the wide array of function in which the nervous 

 system participates, we are led to foresee for each of its cells a great variety of 

 chemical change, or, if when surveying the great differences in function of the 

 organs of the body we are led to expect typical chemical differences between 

 those several parts of the central nervous system with which they are indi- 

 vidually associated, we are arrested by this clear evidence of a universally dis- 

 tributed monotony of simple chemical state. 



It is true that certain drugs affect some groups of cells within this system 

 more readily than others. None of these instances are, however, of such a kind 

 as to demand the inference that there was any essential difference between 

 different groups of cells. In most cases, indeed, it is probable that differences 

 in relative quantity, and in such simple factors as relative state of solution, 

 are responsible for these effects. Thus there is nothing to refute the statement 

 that all the cells of the nervous system contain chemical materials of an exactly 

 similar kind. Just as every liver-cell is like every other liver-cell in their 

 general chemical character, so in the nervous system are all the cells chemically 

 alike. 



Glancing from the liver-cell to the nerve-cell, however, there is at once seen 

 a marked difference of a kind we have not yet considered. The chemical ex- 

 periences of the liver-cell are multifold, but in the main alike for each cell, and 

 it is thus not surprising that the chemical reactions are in the main the same 

 in every cell, no matter how multifold they may be. The physical experiences 

 of the liver-cells are similarly the same for each cell, and we are not surprised 

 that in physical appearance there is as monotonous a similarity between all the 

 cells in the liver as there is monotonous chemical similarity between all the 

 cells in the nervous system. In the nervous system, however, there is no mono- 

 tony in the physical character of the cells. It is a notable physical fact that 

 the cells of the nervous system have diverse shapes and sizes, and still more 

 so that these are such as to bring them into a kind of physical relationship 

 observed in no other epithelial organ. It is a notable physical fact that cells 

 originally separated by considerable distances are brought into close contact 

 by a growth of processes, and that they are in this way arranged into chains 

 forming definite paths for the transmission of physical influence through this 

 system. 



Before attempting to explain the manner in which physical conditions give 

 rise to this arrangement, I must briefly sketch the differences in physical state 

 which may be met with in these cells. Thus there are the states of excitation, 

 of rest, and of inhibition. I may simplify matters by saying that there are 

 reasons for considering excitation as associated with an increase in pressure, 

 either due to a temporary increase of particles in motion within the solutions 

 of the cell or to some acceleration in the motion of particles initially present. 

 In rest these particles are in their normal quantity and have their normal 

 motion. During inhibition the particles are decreased in number, or have a 

 retarded motion. Associating excitation with an increase, inhibition with a 

 diminution, and rest with normal degrees of molecular activity, we shall not be 

 far away from the facts. 



Everyone is aware that increased molecular activity is associated with a 



