Abstract

1. In the intestine of cats cocaine produced depression mainly, which was sometime preceded by transitory stimulation, when the pH of Locke solution was 7.7 to 7.8. When the pH was increased up to 8.5 stimulation predominated, but occasionally this was followed by inhibition. Increased motility was more frequently produced by cocaine when the pH level was 7.5 to 7.0 and the movements of the intestine were practically always stimulated if it was below 7.0.

2. Cocaine, in the same concentrations as were used for the cat intestine, caused depression in the rabbit intestine when the pH of Locke solution was around 7.7. Stimulation occurred very rarely and was followed by depression. Depression likewise occurred when the pH was reduced to 6.5 but it was less than at the higher pH level, as indicated above.

3. In the rat intestine cocaine solutions of medium strength the pH of Locke being about 7.7 or 7.8 produced increased motility, which was less when the pH was about 6.5. A change in pH produced little or no effect on weak concentrations of cocaine.

4. The action of novocaine in any concentration on the rat intestine was not affected by changes in C_H.

5. The mechanism of the action of cocaine was discussed, but no satisfactory explanation of the effect of C_H upon its action in the isolated intestine could be found.