CH. II.] CEREBRAL IMPRESSIONS. 69 



worthy of acceptance ; still, in the course of this work, I shall 

 only consider it as a mere opinion, so that what is true, and 

 what is only probable, may be kept perfectly distinct. 



Note. — Haller seems to object to this doctrine, but his 

 objections appear to be of little importance. He observes, for 

 example, that tubuli of two kinds in the same nerve are not 

 to be distinguished by our senses, and all ganglia seem to be 

 identical with each other. But on similar grounds we may 

 deny the existence of the vital spirits themselves, as they also 

 are invisible. Other arguments of no greater validity are also 

 brought forward as well by Haller as by Monro.^ 



128. When a nerve is compressed by a ligature, or divided, 

 sentient actions are no longer produced by internal impressions 

 in the parts separated from the brain, but are observed only in 

 those still in connection with the brain (31) ; but if the ligature 

 be removed from the nerve, they are again manifested as before, 

 provided the ligature have not destroyed the structure of the 

 nerve. (Haller's ^ Physiology,^ § 367.) But if the nerve be 

 injured by the ligature, its sensibility is destroyed (43) ; hence 

 neither class of impressions can be propagated along either 

 kind of fibril, their progress being impeded by the divided or 

 ligatured portion of the nerve (126, 127). If the brain itself 

 be compressed, as it often is, that portion of the body supplied 

 with nerves from the compressed part of the brain, becomes 

 incapable of sentient actions. The capability returns, however, 

 so soon as the compression of the brain is taken off. When 

 the whole brain is compressed, all animal operations caused by 

 impressions acting on the brain, cease throughout the whole 



' In this paragraph and elsewhere ($§ 487, 488), Unzer advances the hypothesis, as 

 he terms it, of afferent (aufleitenden) and efferent (ableitenden), fibrils in the same 

 nerve. His Gottingen reviewer (probably Haller) thus objects to it : " Herr Unzer 

 considers that it is probable there are afferent and efferent nerves going to and re- 

 turning from the brain ; and that the objections raised against the doctrine are not 

 of much weight. He forgets that the proof rests with himself, for neither experi- 

 mental nor anatomical researches support his conjecture." Unzer replies : " Neither 

 anatomy nor experiment can determine the question; for it is so microscopically 

 minute, as to escape the cognisance of our senses. It was no part of my plan to 

 prove the existence of the two kinds of fibrils. I meditated on certain phenomena, 

 and found that it was absolutely impossible to explain them, except by assuming 

 that afferent and efferent fibrils do exist. The doctrine cannot be absolutely 

 demonstrated; it is but a hypothesis, and I treated it as such." (Physiologische 

 Uutersuchungen, p. 26.) — Ed. 



