1913] Gee: Behavior of Leeches 273 



placed in fresh tap water and allowed to revive. This it did 

 in every case except following magnesium sulphate, which for 

 some reason, though slowest of action, seemed to produce the 

 most disastrous results. The necessity of dermic penetration in 

 all of the substances used made the process sometimes a bit 

 prolonged, but the effect of most of the substances was imme- 

 diately apparent. In no case was the contact stimulus applied 

 sufficient to injure appreciably the animal on which the experi- 

 ment was being performed. 



2. Strychnine 



The effect of strychnine is at first to produce a heightened 

 tonus of the nervous system, accompanied by an increased refiex 

 irritability. In this condition a slight contact stimulus is suffi- 

 cient to cause marked movement, accompanied by tremor or 

 involuntary twitchings of the muscle. The terminations of the 

 motor nerves are paralj'zed by large doses. The enormous activ- 

 ity of the muscles produced as the result of strychnine stimu- 

 lation increases very greatly the consumption of oxygen and the 

 consequent output of carbonic acid, thereby influencing to a 

 great extent the metabolic condition of the animal (Cushny, 

 1910). 



In the experiments on leeches the strength of strychnine 

 found best to employ was a 0.0322 per cent solution. The ac- 

 companying table (see table VIII) and the curve of activity 

 (see fig. 8) plotted from the data in this indicate the general 

 effect produced by strychnine on the leech. The features of 

 the response to strychnine in Dina microstoma are very much 

 the same as recorded by other investigators for the higher ani- 

 mals. Almo.st immediately upon being placed in the solution 

 the leech will respond with marked swimming movements to even 

 a slight contact stimulus of the posterior end. In many instances 

 the animals show reactions such as quick jerks, driving the body 

 irregularly through the water. This type of response affords 

 a very clear example of the heightened reflex irritability. "Within 

 fifteen minutes to a half hour, varying with the individual, the 

 muscles of the specimen become almost entirely relaxed so that 



