2O2 C. M. CHILD AND L. H. HYMAN. 



muscular activity, though how long has not been determined. 

 Sometimes, however, newly attached individuals of H. viridis- 

 sima and H. vulgaris remain quiescent and well extended and 

 show the primary basipetal gradient throughout. 



SUSCEPTIBILITY IN RELATION TO GENERAL EXCITATION, 

 ANESTHESIA AND MUSCULAR PARALYSIS. 



It was noted above (p. 191) that alcohol, ether and the dyes 

 used produce primarily more or less excitation, as indicated by 

 increased muscular activity. This condition is of course followed 

 sooner or later by depression and muscular paralysis, and, ac- 

 cording to the agent and concentration used, death and disin- 

 tegration may occur under conditions ranging from extreme 

 muscular relaxation to extreme contraction and rigidity. The 

 susceptibility relations under these conditions afford further 

 evidence that muscular activity is an important factor in the 

 susceptibility of at least the ectoderm of hydra. 



The degree of general excitation and the rapidity with which 

 depression and paralysis follow excitation and therefore the re- 

 gional differences in susceptibility depend to a considerable ex- 

 tent upon the concentration of the agents used. The lowest 

 killing concentrations of alcohol and ether produce but little ex- 

 citation, and in these disintegration and death usually follow 

 the same course as in detached animals in cyanide (p. 200). Neu- 

 tral red also, in the concentrations used, produces comparatively 

 little excitation, and the susceptibility relations in this agent usu- 

 ally show no special modifications. Methylene blue produces a 

 considerably greater degree of excitation and Janus green is an 

 extreme irritant, and since these dyes accumulate in the cells, 

 even when the external concentration is very low, a considerable 

 degree of excitation occurs sooner or later, even in very low 

 concentrations, but the higher concentrations bring about ex- 

 citation more rapidly and to a more extreme degree than the 

 lower. Only in extreme dilutions of these dyes is the course of 

 disintegration like that in detached animals in cyanide. 



In all these agents, the earlier bud stages preceding the devel- 

 opment of independent motor activity show, as already noted, 

 the same basipetal gradient as in cyanide, except where the bud 



