THE AXIAL GRADIENTS IN HYDROZOA. 2O7 



(Figs. 73-74) and in Janus green are essentially the same as in 

 H. oligactis. The susceptibility of H. viridissima to alcohol, 

 however, is very low, muscular activity continuing for 24 hours 

 or more in 3 per cent., for 3-4 hours in 5 per cent, and for a min- 

 ute or two even in 10 per cent. Alcohol produced but little ex- 

 citation in this species and the disintegration gradient in alcohol 

 is either basipetal throughout or double, as in detached animals 

 in cyanide (pp. 200-202) . The reason for the very low susceptibil- 

 ity to alcohol of this species we have not been able to determine. 

 To cyanide and to ether it is somewhat more susceptible than H. 

 oligactis. In methylene blue H. viridissima shows less excita- 

 t : on than H. oligactis and the course of disintegration is like that 

 of detached animals in non-excitant agents. In Janus green, 

 however, marked excitation occurs followed by paralysis begin- 

 ning in the tentacles and hypostome and the course of disinte- 

 gration is like that in H. oligactis. In other words H. viridissima 

 shows this modification of the primary gradient only in those ag- 

 ents of this group which act most rapidly and most powerfully on 

 H. oligactis. 



H. vulgaris is apparently still less sensitive to the particular 

 effects of this group of agents,, and its motor behavior is less al- 

 tered by them and only in Janus green, the most irritating of all, 

 has the special modification of the gradient been observed. In 

 this agent there is marked excitation ending in strong contrac- 

 tion and rigidity, and the course of disintegration is like that in 

 H. oligactis (Figs. 68-72). 



The fact that alcohol, ether, methylene blue and Janus green 

 all produce the same modifications in the course of disintegration 

 and death in H. oligactis suggests the possibility of a certain sim- 

 ilarity in their action. All produce more or less excitation at 

 first and later paralysis, though the period and degree of excita- 

 tion differ widely. While the data are not adequate to permit 

 definite conclusions, it seems evident from the observed facts 

 that these agents act primarily upon the receptive or sensory and 

 perhaps the transmissive mechanism of hydra and that the modi- 

 fications of motor behavior and the course of disintegration are 

 the indirect results of this action. We should expect the action 

 of alcohol and ether to be of this character, methylene blue is a 



