42 GENERAL ANESTHESIA. 



in the vicinity of the eye, and for all serious operations on horses, whose 

 struggles are particularly violent. Moller recommends anaesthesia in 

 castrating horses with very powerful dorsal muscles. Tn ruminants 

 anaesthesia is seldom resorted to save in difficult parturition. In 

 carnivora, and especially in the dog, its principal indications are 

 in laparotomy, difficult parturition, amputations, and certain opera- 

 tions on the head. 



Anaesthesia is contra-indicated (1) in diseases of the heart (lesions 

 of the valves or myocardium, dilatation, and hypertrophy) ; 

 (2) diseases of the respiratory tract (emphysema, pneumonia, and 

 chronic pleurisy). 



Ether is the best anaesthetic for subjects with emphysema and 

 dilatation of the right heart, chloroform for those with affections of 

 the left heart, chloral when the pulse is intermittent (Arloing). 



Death may be caused by pushing administration too rapidly ; 

 in certain rare cases it may also result from accidents like vomiting, 

 the vomited material passing into the trachea and lungs, and producing 

 mechanical pneumonia. Such a termination is much to be feared 

 in man unless the patient be properly prepared, but it very seldom 

 occurs in the horse. If in operations on the face, such as trepanation 

 of the facial sinuses or nasal cavities, or extraction of molar teeth, 

 an anaesthetic be employed, the head should be placed in a depending 

 position, so as to favour escape of blood, which might otherwise 

 enter the respiratory tract and produce suffocation. 



GENEEAL ANAESTHESIA. 



Narcosis being the result of a special action exerted directly on 

 nerve-centres by the anaesthetic agent, the first necessity is to insure 

 a sufficient quantity of the anaesthetic arriving at those centres. 

 While fixed anaesthetics can be administered by various channels, 

 such as the veins, mucous and serous surfaces, the subcutaneous 

 tissue, etc., volatile anaesthetics must penetrate by the respiratory 

 mucous membrane. Injected into the tissues or veins, fixed anaes- 

 thetics traverse the pulmonary capillaries wit In ml sensible change, 

 and act promptly on the nerve-centres ; volatile anaesthetics, 

 similarly administered, escape in large measure through the walls 

 of the pulmonary vessels, are expired, and fail to reach their 

 destination in sufficient quantity to produce much effect. On the 

 other hand, volatile substances, introduced in a state of vapour into 

 the respiratory tract, are freely absorbed by the blood circulating 



