Abstract
Procedure.—Cats were subjected to the action of dimethyl sulphate fumes in a concentration of 4.5 to 10,000 of air for one hour. The dimethyl sulphate, which is a liquid at ordinary temperatures with a specific gravity of 1.32 and a boiling point of 188° C., was vaporized by an electric hot plate in the gas chamber. An electric fan in the gas chamber kept the available fumes mixed with the air. The temperature of the gas chamber was maintained between 25-30° C.
With this strength of gas the cats usually succumbed in 30-60 hours.
In cats which are gassed as described above a strong generalized analgesia is observed within a few hours after exposure to the dimethyl sulphate fumes, and reaches a high degree within twenty-four hours. If the animal survives, the analgesia may still be well marked six months afterwards.
In such animals severe operations may be performed without any anaesthetic and without eliciting any or only slight indications of pain. Thus, for example, the femoral artery may be dissected free, tracheotomy performed, the vagosympat hetic trunk exposed in the neck, the tibialis anticus muscle dissected free, the peritoneum opened and the parietal walls rubbed by an inserted finger, or gentle traction exerted upon the gut, without causing any or at most only slight signs of pain. Severe compression of the tail, toe pads, nasal septum, lip, ears, cause no sign of pain, though the tail is twitched aside, the foot withdrawn, the head turned away or the ears flattened against the head when the pressure stimulus is stopped.
The loss of pain perception was, however, not complete in any animal : blunt dissection of a mixed nerve which stretched it or electrical stimulation of the sensory nerve, always caused more or less restlessness of the animal, but never to the degree which is obtained by the same manipulation in a partially anaesthetized cat.
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