14 Surgical Diseases and Surgery of the Dog 



quently it can not be regarded as a satisfactory test. The first effect 

 of chloroform on the pupil is dilation from excitement, varying in 

 degree and duration in different individuals. Coincident with the 

 approach of the stage of narcosis and fall of blood-pressure, the 

 pupil commences to contract and continues to do so slowly until 

 either the return of sensibility or the stage of asphyxia. The stage 

 of complete or operative narcosis is reached when the pupil no 

 longer dilates in response to otherwise painful stimuli. It is the 

 degree of contraction which must govern the administrator in the 

 exercise of his judgment as to the quantity of vapor permissible. 

 Should the pupil become strongly contracted and immobile the 

 danger point is reached and the vapor must be immediately with- 

 drawn and fresh air supplied. Otherwise, the pupil will be seen 

 to dilate suddenly and completely and almost at the same time the 

 breathing will cease, an indication of vaso-motor paralysis and as- 

 phyxia, a state from which it is difficult or impossible to resusci- 

 tate the animal. There 'is, therefore, no pronounced change 

 to give warning of impending danger, and as soon as the pupil is 

 strongly contracted the supply of vapor must be cut off and air sup- 

 plied until dilation again commences, when, if necessary, more vapor 

 may be supplied and withdrawn as before, and this procedure kept 

 up until the completion of the operation. 



To resuscitate from the asphyxial condition free access of 

 air to the lungs must be secured. The inhaling mask is cast aside 

 and the tongue grasped and drawn forward. Artificial respiration 

 Is then resorted to. The effect is twofold. It not only brings 

 fresh air to the alveoli, but acts as a mechanical heart-stimulant and 

 restorer of blood pressure. Hence to be effectual it should be mod- 

 erately vigorous to the point of compressing the chest. A good plan 

 is to suspend the animal with the head downward. It is believed that 

 this causes a determination of blood to the brain to stimulate the 

 flagging centers, and the vapor of the drugs being heavier than air 

 tends to gravitate. 



Some practitioners place much confidence in medicinal anti- 

 dotes, such as the vapor of ammonia, medicinal doses of official 

 dilute hydrocyanic acid, hypodermic injections of ether and strych- 

 nine, but it should be remembered that if the respiration and circu- 

 lation are nearly at a standstill, drugs have little chance of being car- 

 ried to the vital centers, and moreover, many valuable seconds may 



