PRELIMINARY OPERATIONS 357 



some cotton sponges, a bottle of alcohol (95%), a bottle of 

 tincture of iodine, a large pan containing a liter of water 

 and a bottle of liquor cresolis compositus. Two or three 

 sterile towels may be used to advantage. 



The operator washes and scrubs his hands thoroughly 

 with soap and water and waits for the assistant to prepare 

 the animal. 



When all preparations are made a dog weighing prefer- 

 ably about ten kilos is gently placed on its left side on the 

 operating board and tied down. Do not excite or scare 



Fig. 303. Metallic muzzle (made of sheet brass) for administering an anesthetic to 

 a dog by the closed method. A heavy, perforated rubber membrane is tied (with wire) 

 over the rear end of the muzzle. The animal's nose and mouth are thrust through the 

 opening in the rubber membrane. 



the animal. Nitrous oxide and oxygen are then admin- 

 istered to the animal until it becomes unconscious. This 

 is best done with an apparatus like those shown in Figs. 

 116, 118, and 172. It usually requires at least ten minutes 

 to get a dog fairly deeply anesthetized with nitrous oxide 

 (and oxygen). It is assumed that the students have previ- 

 ously had some experience in giving nitrous oxide to dogs 

 in the experiments in the earlier part of the course. The 

 animal has the metal muzzle (Fig. 303) placed over its nose 



