Forty-two atropinized dogs of both sexes were given a standard dosage (3.0mg/ kg of body weight) of xylazine subcutaneously and divided into 4 groups. When fully sedatated, the dogs were given ketamine intramuscularly : Groups A and C 5.0mg/ kg, and groups B and D 10.0mg/ kg. Then at the stage of surgical anesthesia, dogs in groups A and B were given the combination of 4-aminopyridine (4-AP; 0.3 mg/ kg) and yohimbine (YO; 0.125mg/ kg) intravenously. Dogs in groups C and D free from 4-AP and YO were used as the control.
In group A, the mean initial response time (RT ; time from administration of combination of 4-AP and YO to cognition and ability to lift up head) decreased to 2.8 min compared with 47.6 min in group C (control) . Mean alert time (AT; time to cognition and ability to wake up) decreased to 4.3 min (control 53.0 mm) . Mean stand-up time (ST; time to cognition and ability to stand-up) decreased to 7.0 min (control 60.0 mm) . And mean walk time (WT; time to cognition and ability to walk) decreased to 11.3 min (control 65.4 mm) .
In groups B, administered the combination of 4-AP and YO, mean RT decreased to 4.3 min compared with 59.7 min in group D (control) . Mean AT, ST and WT decreased to 6. 5, 15.5 and 24.2 min, compared with those of 64. 0, 71.6 and 79.0 min respectively.
In comparison with respiratory rates observed at the surgical stage of anesthesia (8-36 breaths/min), rates after the initial response time were increased about two times (25-54 breaths/min) . And respiratory depth was increased clinically. Relapses to unconciousness did not occur. No signs of anxiety, excitation and convulsant tendencies were marked.
Result of this study shows that the combination of 4-AP and YO is a safe, fast-acting and specific antagonist of xylazine and ketamine combination anesthesia in dogs.

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Measurement of the trachea of 10 mongrel dogs (8 males and 2 females), each weighing 10 kg, was carried out to study the general length of the trachea and the amount as well as the lengthwise and breadthwise diameters of the cartilagines trachealis. Observation was also made on the appearance of the endotracheal tube using radiograph and endoscope.
The results are outlined below:
1. Study was made to discover a constant in the ratio of the length of the trachea in comparison with the body weight, the body length, the body height, the circumference of the neck and shoulders, and the length of the neck. A constant of 0.6 to 0.7 was obtained on the ratio of the body weight to the length of the trachea. However, a constant ratio on other comparisons was not possible. Moreover, the number of cartilagines trachealis varied widely from 33 to 46 in the animals.
The breadthwise diameter of the cartilagines trachealis gradually increased in size from the 1st to the 5th and 9th, which were the largest, then gradually decreased in size. As to the lengthwise diameter of the cartilagines trachealis, the 1st was the largest with subsequent ones gradually decreasing in size toward the tracheal-biffureation.
From the foregoing, it can be concluded that an endotracheal tube with an exterior diameter of 10 mm is suitable for the trachea of dogs weighing 10 kg.
2. Observation using radiograph and endoscope indicates the area between the 1st to the 12th cartilagines trachealis as being the position suitable for the placement of the call. Moreover, to obtain airtight sealing point, a minimum Gaff air pressure of 2 to 3 ml was found to be suitable.

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