328 LECTURE XIV. 



particles of the internal matter, the cell-contents. In these 

 cases therefore it is not so much the real cell in its pure 

 form which decides the question, as the specific matters 

 with which it is provided internally ; the chief agent is 

 not so much the membrane or the nucleus of the cell, as 

 the contents. It is these which, when exposed to cer- 

 tain influences, become comparatively rapidly changed, 

 without our being always able morphologically to de- 

 tect any trace of a change in the arrangement of the 

 contained particles. The utmost that we can observe in 

 the shape of a palpable result is a real locomotion of 

 small, visible particles, but we cannot push our analysis 

 to such an extent, as to enable us to form any opinion 

 as to the internal cause, in virtue of which this locomo- 

 tion is effected by the ultimate particles which compose 

 the cell-contents. When an excitation takes place in a 

 nerve, we now know that a change in its electrical state 

 is connected with it, a change which, from all that is 

 known to us concerning electrical excitation in other 

 bodies, must of necessity be referred to a change in the 

 position which the individual molecules 

 assume to one another. If we conceive 

 the axis-cylinder to be made up of elec- 

 trical molecules, we can easily imagine 

 that every two of these molecules take 

 up an altered position with regard to 

 one another at the moment the stimulus is applied. Of 

 these processes we see nothing. The axis-cylinder looks 

 just as usual. If we watch a muscle during its contrac- 

 tion, we remark, it is true, that the intervals which sepa- 

 rate the individual so-called discs (p. 82) become shorter ; 

 and as we now know that the substance of the mus- 



Fig. 97. Ideal diagram of the condition of the molecules of a nerve when it is 

 at rest (in a peripolar state, A), or in an electrotonic (dipolar) state, B. From Lud- 

 wig, ' Physiolog.,' I, p. 103. 



