1903.] 



in the Nerves of Warm-blooded Animals. 



267 



The question of temperature will be considered later. Assuming 

 for the present purpose that the conditions of experiment were equally 

 favourable throughout, and taking the sciatic nerve as a standard, 

 different animals gave the following values : — 





Milliv 



Maximum 

 observed. 



olts. 

 Mean. 







1 -1 



0- 66 



1- 05 

 1-2 



0-69 

 -50 

 0-42 

 0-89 



Mean of 11 experiments. 

 5 



9 



)> w >) 



All these are very much less than the frog, which gives 2 millivolts or 

 more. 



Different nerves in the same animal often show individual inequali- 

 ties, but as a rule the larger nerves give a smaller negative variation 

 than those of less diameter. The sciatic gives commonly the least, 

 but is the most resistant to adverse influences. The median and 

 ulnar nerves are more delicate, but give larger variation under favour- 

 able circumstances, e.g., the median nerves of the pigeon gave a mean 

 value of 0*54 millivolt (five experiments) as against 0-42 for the 

 sciatic. The greatest value I have yet measured was in a branch of 

 the anterior crural of the rabbit, which on the right side gave 2 - 5 milli- 

 volts and on the left 2*3. 



Boruttau* found the vagus in the rabbit to give a larger negative 

 variation than the sciatic, and obtained only very small responses from 

 the nerves of hens, ducks, or pigeons. 



The larger number of fibres not in contact with the longitudinal 

 electrode would appear to act as a deriving circuit of less resistance in 

 the larger nerves, and so less current passes through the galvano- 

 meter, and the greater amount of connective tissue in the sciatic 

 would have the same effect. It is possible that there are other causes 

 in addition to these ; there is at present no evidence for or against 

 such a possibility. 



Similar reasons probably also explain why a stronger stimulus is 

 necessary for the warm-blooded nerves than for the frog. The 

 difference is, however, not very great. The minimal effective excita- 

 tion I have so far observed is 6 units of the " Berne " coil, 500 units is 

 commonly a maximum, 1000 nearly always so. The smaller electrical 



* Boruttau (a), loc. cit. 



