86 PARALYSERS OF SENSORY NERVES 



Sensory nerves are readily affected by many drugs ; their 

 local effects are comparatively easy to determine ; but when 

 the drug enters the circulation many structures are liable 

 to be affected, and definite results are difficult to obtain. 

 Much trustworthy information has, however, been got by 

 experiments on frogs, chiefly by ligaturing the sciatic artery 

 of one leg, injecting into another part of the body the drug 

 to be tested, and by pinching, pricking, heat, or electricity, 

 noting the difference in sensation between the poisoned limb 

 and the ligatured unpoisoned limb. By these and other ex- 

 periments it has been demonstrated that nervous sensibility 

 is diminished by aconite, veratrine, belladonna and atropine, 

 carbolic acid, and chloroform. Hydrocyanic acid exerts 

 topical paralysing effects on sensory nerves. Notable 

 reduction of the sensibility of sensory nerves is likewise 

 effected by several members of the aromatic series of carbon 

 compounds, such as exalgin (methyl-acetanilide), antifebrin 

 (acetanilide), and antipyrine (phenazone). Diminishing 

 excitability of sensory nerves, such agents relieve pain, and 

 are accordingly anodynes. Others exert marked paralysing 

 effects on the terminals of cutaneous nerves, temporarily 

 destroy sensibility, and hence are useful local anaesthetics. 

 Among these are cocaine and its allies, ether spray, cold, in 

 the form of ice or freezing mixtures, and carbolic acid. 



The irritability of sensory nerves is increased by topical 

 or cants. Aconite and veratrine, whether applied locally, 

 irritarried through the circulation, produce at first peculiar 

 numbness and tingling of the tongue and lips, and indeed 

 of all parts supplied by the fifth nerve, to be followed by 

 depression and lessened sensibility. 



Electrotherapy constitutes an important method of treat- 

 ment in human medicine, but in veterinary practice its 

 application is limited to the occasional use of Faradism or 

 Galvanism. The faradic, alternating, or induced current 

 is serviceable in peripheral paralysis where muscular stimula- 

 tion is required, as in the treatment of equine facial, radial, 

 or crural paralysis, and of similar conditions in the dog. 

 The Galvanic, Voltaic, or constant current is most useful in 

 cases where definite chemical change in the tissues is re- 

 quired. Insulated needles placed in the tissues and tra- 



