256 On the Effects of certain Physical and 



removing the head, the viscera, the integuments, and de- 

 nuding the brachial and lumbar nerves, so as to expose 

 them to the influence of the atmosphere, placing the frog on 

 a plate of glass, vi^ith its nerves raised and suspended as it 

 were, so as to be free from contact with the glass, or any 

 structure which could retain moisture, the arms and legs 

 being drawn laterally and downwards ; we watched the effect 

 of gradual desiccation of the nerves. In a moderate space 

 of time slight movements were observed in both anterior and 

 posterior extremities, but especially in the latter, and slight 

 flickei'ings of the muscles, gradually augmenting as the nerves 

 assumed the dusky colour and dulness of aspect induced by 

 evaporation . 



We now moistened the lumbar nerves (by laying over them 

 the viscera of the animal previously removed) ; all movements 

 ceased forthwith. We repeated the experiments on the same 

 animal, allowing the nerves to become di'y, and then re-apply- 

 ing the natural moisture, with precisely the same effect, seve- 

 ral times. 



We again allowed the lumbar nerves to become slightly de- 

 siccated, and when the movements in the lower extremities 

 wei*e most obvious and distinct, we divided the nerves, first 

 clt)se to the spine, without any effect, and then close to the 

 inferior extremities, with the instant and total cessation of 

 all movement. 



I need scarcely add, that these effects of desiccation must 

 be most carefully observed and appreciated, and distinguished 

 from the electrogenic effects of the Voltaic influence. 



We now prepared a frog, as represented in fig. 1, leaving 

 the lumbar nerves in contact with the posterior soft and humid 

 tissues of the back. It was now impossible, by any means, 

 to induce the sudden spasmodic tetanoid contraction of the 

 muscles on breaking the Voltaic circuit, after causing the 

 current to pass through those nerves, during periods of time 

 which would have cei'tainly produced those effects had the 

 animal been prepared as in fig. 3, the nerves being detached 

 and insulated from the humid tissues beneath. 



We prepared another frog, as in fig. 3, and, keeping the 

 nerves constantly wet with a layer of water applied over 



