CH. III.] EXTERNAL SENSATIONAL ACTIONS. 105 



201. If external sensations develope actions directly in me- 

 chanical machines, they re-act by means of their material ideas 

 along the same nerve that received the impression (188). 

 Hence it would follow (contrary to observation), that all me- 

 chanical machines, in which a branch of the same nerve is dis- 

 tributed, must be all put into action at once by every external 

 sensation of the nerve, unless it be granted, either that the 

 impression which excites an external sensation in the brain 

 at the point of origin of the nerve, can only act upon certain 

 fibrils of the brain in connection with one or a few branches 

 going to certain mechanical machines, which fibrils do not 

 accompany other twigs of the same nerve (188); or, that (136 

 et seq.) there are certain natural hinderances to the transmis- 

 sion of the cerebral impressions (136, iii), or, that it is turned 

 aside, or conducted away, in its course along the nerve from 

 various mechanical machines, and permitted to reach only those 

 appropriate to it, as is detailed ante (136 — 139, also 165, vi). 



What influence sleep (49, 136, iii), and habit (51, 139), and 

 the ganglia (48, 137), may exercise in this respect, ought also 

 to be considered. It is probable, that all these hinderances 

 actually occur in nature. 



202. The mechanical machines can develope nerve-actions 

 (183), but no sentient actions, if the brain, or the cerebral 

 origin of its nerves, or of those special fibres of the nerve 

 which receives and transmits the external impression appropriate 

 to the sensation (126), be compressed, or their function des- 

 troyed ; or if the course of the nerve or of the fibrils be inter- 

 rupted between the brain and their terminating fibrils (128, 

 164, iii, iv): also when the function of the mechanical machines 

 themselves are interrupted (129, iv). 



208. The direct sentient actions developed in the various 

 mechanical machines by external sensations, are as varied as 

 the adaptations of the machines themselves to impressions (193). 

 We will consider their functions more in detail with reference 

 to this point. 



204. The sentient actions of external sensations excite con- 

 tractions in muscular tissue which, when violent, are termed 

 spasms. Spasms, frequently repeated, are . convulsions ; if con- 

 tinuous, they are tetanic [Erstarrungen] . The limbs moved 

 by the muscles thus aff'ected, and the other functions which the 



