274 University of California PuMications in Zoologij [Vol. 11 



the animal is scarcely able to respond to the stimulus by even 

 so much as local contraction of the area affected. At this stage 

 the leech becomes so flaccid that it can be removed from the dish 

 over a needle, much as might be done vpitli a piece of ribbon. 

 Within a couple of hours after removal of the specimen to a 

 dish of clean water the poisons have so far dissolved from the 

 system that the animal can perform slow co-oi"dinated swimming 

 movements in response to stimulation of the posterior end. By 

 the next day it has recuperated to the extent that its responses 

 appear normal. 



3. Nicotine 



Cushny (1910) says with regard to the effect of nicotine on 

 the lower organisms: "Nicotine has but little toxic action on 

 the lowest invertebrates, but as the nervous system begins to 

 be differentiated it causes paralysis, and still higher in the scale 

 paralytic action is preceded by a stage of stimulation." 



When a leech is placed in a 0.00066 per cent nicotine solution, 

 a much increased responsiveness to stimulation is produced. This 

 fact is very apparent upon comparing the curves of activity 

 (see fig. 9) produced by nicotine and strychnine. The strength 

 of nicotine used incites a much more vigorous activity even than 

 strychnine, depression also being produced more rapidly. A 

 clear gelatinous secretion, apparently of mucin, is produced over 

 the surface of the body upon its introduction into the nicotine 

 solution. This doubtless serves, to a certain extent, as a pro- 

 tective coat for the body. It makes stimulation somewhat more 

 difficult to gauge, but with ten individuals comparing so uni- 

 formly in general character of response, the source of error from 

 this cause must be extremely constant, or very slight. 



The movements produced by contact stimulation under the 

 influence of nicotine are decidedly more abnormal in character, 

 as well as in duration, than were those due to strychnine. Within 

 a short time after introduction into the dish the portion of the 

 body anterior to the clitellum became closely constricted. This 

 contraction of the circular muscles later extended to the pos- 

 terior regions of the body. Finally paralysis ensues, and the 

 animal becomes incapable of progressive movement. If the leech 



