SECT. III.] PROPERTIES OF THE VIS NERVOSA. 397 



being therefore undiminished, a slower motion of the humours 

 and an agreeable coolness from the diminished action of the 

 heart only ensues.^ The celebrated Fontana infers, from his 

 experiments, that opium does not diminish the amount of that 

 power by which the nerves move the muscles, but that it is the 

 spirit of wine which, whether used as a solvent of opium, or alone, 

 renders them insensible to irritation, and destroys that property 

 of the nerves which controls the muscles. ^ The latest opinion 

 of Haller as to these experiments is, that they partly require 

 confirmation, and partly admit of another explanation ; and he 

 ends his opinion with these words : " Lastly, from the remark- 

 able effect which opium produces on the stomach and intestine, 

 there is ground for suspecting that the vis insita is diminished 

 by opium as well as the vis nervosa.''^ But it has already been 

 abundantly proved by distinguished men (and it will be shortly 

 rendered more evident), that the vis insita of Haller, or irrita- 

 bility, is dependent upon the vis nervosaj and cannot exist 

 without it; and, consequently, as opium diminishes the vis 

 nervosa, it is thus only that it diminishes irritability, or the 

 vis insita. 



vi. The vis nervosa is divisible, and exists in the nerves in- 

 dependently of the brain, — Vis nervosa is as divisible as the ner- 

 vous system, so that it remains in each portion of a bisected 

 nerve, as if it were still entire and connected with the brain. 

 Nor does the vis nervosa of the nerves require continual supplies 

 from the brain, since nerves possess their own vis nervosa, 

 which never had a connection with the brain. The experiments 

 that prove this have long been perfectly well known ; namely, 

 that if a nerve be cut or tied, although by these means its 

 connection with the brain be destroyed, it is still as able, if 

 irritated, to cause the muscles to contract as if its connection 

 with the brain were entire. Haller clearly states this fact in 

 many places.* He observes : " a nerve compressed or tied, and 

 then irritated below the ligature, excites those muscles to con- 

 vulsive contraction, to which it is distributed, just as if it was 



• Dissert. Demonstrans Opium vires Fibrarum cordis Debilitare, et Motum tameii 

 sanguinis augere. Monasterii, 1775. 



2 Vid. Halleri Oper. Min., torn, i, p. 487. 



3 De Part. Corp. Hum. Fabr. et Usu, tom. ii, pp. 391, 392. 



* El. Phys., tom. iv, p. 337. 



