732 DH FRASER ON THE PHYSIOLOGICAL ACTION 



for other twenty minutes ; with the same negative result in the case of the uncut nerve, and with 

 continuation of activity in the cut one. The energy of the contractions then gradually 

 diminished ; hut the distal portion of the cut nerve was not paralysed until twenty-eight 

 minutes after the loss of motor nerve conductivity in the portion of its trunk proximal to the 

 spinal cord, as well as in all the other nerves of the hody. 



Experiment XXXII. 



In a second experiment, the distal portion of the divided nerve retained its conductivity 

 forty-five minutes longer than the undivided nerve. 



Another experiment contains some further results, which are worthy of being 



shortly mentioned. 



Experiment XXXIII. — {Temperature of Laboratory, 56° F.) 

 Performed in August 1866. 



I exposed a small and equal portion of each sciatic nerve in a frog weighing 515 grains, 

 and cut through the right nerve-trunk. One grain and a-half of extract was then injected into 

 the cellular tissue under the skin of the hack. 



In one hour and thirty minutes, no variety of stimulation could excite reflex movements : and 

 when the left, or uncut, sciatic was then gently galvanised," faint contractions of the left toes were 

 all that was produced ; while the same interrupted current caused vigorous contractions when 

 applied to the distal portion of the cut nerve. This condition continued, the contractions produced 

 by the left (uncut) nerve becoming gradually fainter, until three hours and twenty-two minutes 

 after the poison had been injected, when this nerve became perfectly paralysed, as well as all the 

 other motor nerve fibres and the proximal portion of the cut sciatic. The distal portion of the 

 cut (right) sciatic seemed all this time quite unaffected ; and when it was galvanised, the muscles 

 with which it was connected contracted with vigour. This condition lasted for fifteen minutes, 

 when galvanism of the uncut nerve again produced a faint twitch of several of the left toes. By- 

 and-by, it recovered all its former activity, and the return to vitality was shared in by the 

 other temporarily paralysed nerves. On the following morning the frog was perfectly well and 

 jumping about. 



From such data it cannot be concluded that the motor nerve fibres are para- 

 lysed by a centripetal progression of the poison. There seems only to be a connec- 

 tion between the rapidity of paralysing effect, on the one hand, and the subdivision 

 of nerve substance with facility of contact of poison, on the other ; as the motor 

 trunks were undoubtedly affected when it was impossible that they should be 

 influenced by an extension of the poisonous action from their endorgans. I can- 

 not advance any very satisfactory explanation of this delay in the action. Pro- 

 bably it is caused by the irritation of the vaso-motor nerves in the trunk of the 

 sciatic, which the section of the latter at first produces, and which is followed by 

 contraction of the capillaries in the parts supplied by them.* During this con- 

 traction, a much smaller quantity of poison-bearing blood is brought in contact 

 with the endorgans of the cut than with those of the uncut nerve, and, as a very 

 prolonged contact of the poison appears necessary, this may be sufficient to account 

 for the delay ; while the recovery from the irritation of the section, which soon 



* Such contraction has been directly demonstrated by Ltster and others after division of the 

 sciatic nerve. See " An Inquiry regarding the parts of the Nervous System which regulate the 

 contraction of the Arteries;" Philosophical Transactions, 1858, vol. cxlviii., p. 607. 



