652 EAYMOND PEARL. 



TTjy per cent. — Negative reaction, but decidedly less pro- 

 nounced than with preceding concentrations. Does not 

 cause any movement whatever in resting specimen. 



^ per cent. — Negative reaction, less strong than in pre- 

 vious cases. In some cases positive reaction. Noticeable 

 tendency to give slight positive reaction just before the 

 definite negative response. 



•g\p per cent. — Well-marked positive response. 



Summary. — The same conclusions are to be drawn from 

 the experiments on organic acids as from those on mineral 

 acids, viz. that to strong concentrations of a given substance 

 the negative reaction is given, while weak concentrations 

 cause a positive response. Oxalic acid is rather peculiar in 

 that it appears to furnish in all concentrations a stimulus of 

 the proper quality to induce the positive response, but is at 

 the same time excessively harmful in any above the weakest 

 solutions. 



Al kalies. 



Sodium Hydrate, i per cent., j^jy per cent,,and ^V P^i" 

 cent. — Immediate strong negative response. Specimens 

 turn away very sharply. In — per cent, the reaction is 

 slightly weaker than in the other two. 



J^ per cent. — Negative reaction. Stimulus applied to pos- 

 terior end of body is sufficiently strong to cause crawling 

 movement. 



yL per cent. — Weaker negative reaction. Sufficiently 

 strong to start resting animal into movement. 



jjrjj- per cent. — Weak negative reaction. Ineffective on 

 resting worm and on posterior end of body of moving 

 specimen. 



-^^ per cent. — A^ery weak negative response. In one 

 specimen sharp positive reaction ; performs whole food re- 

 action on the end of the tube. 



-^^-^ per cent. — Positive reactions from all specimens. The 

 complete food reaction is given. 



