PRINCIPLES OF VETERINARY SURGERY 249 



fact that the toxicity of the chemical anjesthetics renders 

 their too free and too promiscuous application quite hazard- 

 ous. 



DEFINITION.— The term "local anaesthesia" refers to 

 the relief of surgical pain in a circumscribed area. It is 

 accomplished by the, use of drugs called local anaesthetics. 

 The area, although generally circumscribed, may by their 

 application to a large nerve trunk, extend over a considera- 

 ble surface. Thus, by injecting cocaine upon the plantar 

 nerve the entire foot may be rendered insensible. 



The local anaesthetics in general use in veterinary prac- 

 tice are cocaine hydrochlorate, in a 4% to a 10% solution; 

 eucaine hydrochlorate in a 5% to a 10% solution; ethyl 

 chloride; morphine sulphate in a 10% solution with cocaine 

 hydrochlorate 5%; adrenalin chloride 0.01% with chlore- 

 tone, I % ; mixtures of cocaine, morphia, carbolic acid and 

 sodium chloride in proper strengths; and stovane. 



The chief one is cocaine hydrochlorate in a solution 

 varying from 4% to 10%, according to the surface to be 

 anaesthetized. From the standpoint of efficacy it cannot 

 be easily supplanted, although excellent effects are ob- 

 tained when it is mixed with morphia, carbolic acid and 

 sodium chloride. Eucaine is somewhat less toxic, but also 

 less effectual as an anaesthetic. Ethyl chloride is admirable 

 as a spray to the surface after cocaine has been injected 

 subcutaneously, and to spray upon the tissues as the opera- 

 tion proceeds. It is practically non-toxic. 



ACTION OF COCAINE.— When cocaine at 5% is 

 applied to a mucous membrane or to the skin deprived of 

 its epithelium, it rapidly deprives the seat of application of 

 all its sensibility. After a fev/ minutes it produces an 

 anasmic condition of the part by constricting the vessels. 

 The sensibility begins to return in about twenty minutes. 

 The insensibility is very superficial, for cocaine does not 



