THE REACTIONS OF CRAYFISHES TO GRADIENTS OF DISSOLVED CARBON DIOXIDE AND ACETIC AND HYDROCHLORIC ACIDS

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Abstract
1. Crayfishes sense the increase in carbon dioxide and acetic and hydrochloric acids in a gradient. 2. Both propinquus and virilis are intoxicated by carbon dioxide; virilis is also intoxicated by acetic acid but to a lesser degree. 3. The four species are susceptible to high concentrations of carbon dioxide and when subjected to high concentrations die in the following order, virilis, propinquus, diogenes and immunis. 4. Propinquus reacts negatively to the higher concentrations of carbon dioxide in a gradient, but when the total amount of acid present is large, the negative reaction may be interfered with by the direct detrimental effect of the acid. 5. Virilis reacts less definitely to the higher concentrations of carbon dioxide in a gradient than does propinquus. This is true whether the total concentration of the acid is large or small. 6. Both diogenes and immunis react more or less irregular to carbon dioxide due possibly to the lesser sensitiveness of these two species to this acid. 7. Both propinquus and virilis react negatively to the higher concentrations of acetic acid in gradients of this acid; propinquus reacts definitely in the presence of both high and low total concentrations; virilis reacts definitely to low total concentrations, but not so definitely to high total concentrations; diogenes reacts irregular and less intense than the first two species while immunis reacts more definitely but with low intensity. 8. All four species react more strongly to hydrochloric acid than acetic acid and more strongly to acetic acid than carbon dioxide. 9. The intensity of avoiding reactions of all species to all acids tested as is shown by turnings only are in the following order; propinquus, virilis, immunis and diogenes. 10. The intensity of avoiding reactions of all four species varies directly as the total concentrations of the acids, and probably directly as the hydrogen ion concentration. 11. Rapid modification of behavior is shown by all four species. This modification may be due to the increased sensitiveness on the part of the animals, the increased sensitiveness being the result of higher ion concentration in the animal's blood. 12. The specific reactions of the crayfishes in gradients of carbon dioxide may be correlated with their habitats.

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