34 CEREBRAL FORCES. [i. 



be distinguished^ for otherwise the doctrines as to the recriprocal 

 influence of body and soul can only be indistinctly and inde- 

 finitely comprehended. We have, therefore, for want of more 

 elegant expressions, determined to designate sensations of the first 

 c\a,ssea^ternalj and of the second internal, and never to vary from 

 these terms, except when we use the verb to feel, in the third, 

 general, or indefinite meaning, when it is not necessary to say 

 whether external or internal sensations are meant. The reader 

 will sometimes find it necessary in the sequel, to remember these 

 remarks. 



35. A true external sensation is never excited without there 

 being an external impression on the nerves, and consequently 

 the latter is rightly considered the only primary animal force (6), 

 whereby the soul feels. But since external sensations are con- 

 ceptions which cannot possibly arise without material ideas in 

 the brain (25), it follows that in each case an external impres- 

 sion must excite a material external sensation in the brain, and 

 itself develop true external sensations, independently of the 

 co-operation of the conceptive force.^ 



» The Gottingen reviewer of Unzer's work, referring to this doctrine as to the 

 development of external impressions into material ideas (the "species" of Haller), 

 objects "that nerves pass from and to the spinal cord and enter it, and, conse- 

 quently, that the external impressions made on them ought to be developed therein 

 into material ideas ; yet it is certain that the soul neither feels nor has its seat in 

 the spine." This and other objections raised against Unzer's views in this review 

 are the more interesting, because it seems probable that Haller was the writer, and 

 because it gives Unzer an opportunity of explaining some points more fully. He 

 then replies to the objection : — " Although this is hardly advanced as an objection, 

 and although I have not only not neglected to notice the matter referred to, but 

 have entered into details in illustration ; still it is sufficiently important to merit 

 further consideration. It is not merely a change caused at the origin of a nerve by 

 impressions, that induces sensation and thought, but it is always necessary thereto, 

 that there be a cerebral tissue into which the nerve must penetrate. Since new 

 fibrils frequently pass out from the ganglia, it might be inferred that all might feel ; 

 but as there is that peculiar structure wanting in them, which is present in the brain, 

 and is subservient to the formation of material ideas, the change which the nerves 

 undergo in the ganglia from external influences, is only a motor force — a reflexion 

 of the impression upon other nerve-fibrils, — and which has been fully explained 

 already in my work (399, 421). It is the same with the nerves which arise from 

 the spinal cord, and which probably have the twofold function of transmitting to the 

 spinal cord the impressions they receive, that they may be sent directly forwards to 

 the brain and subserve to sensation ; or that they may be reflected in the spinal 

 cord on other nerves, and thus induce certain movements which otherwise would 

 not have resulted from these impressions." — Physiologische Untersuchungen, p. 24. 

 Compare also § 624.— Ed. 



