12 Surgical Diseases and Surgery of the Dog 



elusion of the respiratory tract. When the head was depressed 

 slightly there was rattling in the throat, but the secretions did not 

 penetrate any further. When the head was allowed .to hang free, 

 the secretions escaped from the mouth and none were inspired, but 

 when with the head thus held the fluids were prevented from escap- 

 ing they were inspired. Hence, in the administration of ether the 

 position of the head is a matter of great importance and must be 

 such as to permit of drainage of the buccal secretions. Rattling in 

 the throat is significant of their inspiration, and is to be avoided. 

 Vomiting is also more apt to occur with ether, and this with labored 

 breathing is productive of inspiration-pneumonia. 



For the safe administration of either of these drugs a certain 

 proportion of air is necessary. This is particularly true of chloro- 

 form to which a large admixture is essential for safety. The pro- 

 portions have been worked out by Bert. He found that when the 

 anesthetic vapors and air were mixed in certain definite proportions, 

 and continuously inspired, safe anesthesia was established. If the 

 proportion of the medicamentary substance was increased, death re- 

 sulted. The interval between the anesthetic and lethal dose he 

 designated the "maniable zone." In carefully determining the 

 limits of this zone with various agents, he arrived at the singular 

 conclusion that in every instance the lethal dose is precisely double 

 the anesthetic. 



To illustrate, the following table is useful : 



The figures indicate the number of grams of the anesthetic 

 liquid mixed with loo liters of air, and then reduced to vapor. 



If an animal is made to inspire a mixture corresponding to 

 about the middle of the maniable zone, it is rapidly anesthetized and 

 will remain so as long as the administration is continued. But the 

 maniable zone is singularly limited, a few extra drops converting 

 the active dose into a lethal one. This is particularly true of chloro- 

 form. Eight grams volatilized in one hundred grams of air did not 



