ANIMAL AND VEGETABLE 189 



remarked elsewhere, is fifth in the scale of electro-positives 

 and oxygen at the bottom of the list of electro-negatives ; 

 and providing that osmosis can take place and there is an 

 exciting solution, such electrical action may very well occur. 



Upon the assumption that it does so occur let us See 

 how the movements of the amoeba are affected by 'stimuli. 



" (1) CHANGES OF TEMPERATURE. Moderate heat 

 acts as a stimulant. The movement stops when the 

 temperature is lowered near the freezing-point or raised 

 above 45 C. 



" (2) CHEMICAL STIMULI. Distilled water first stimu- 

 lates, then stops amoeboid movement. In some cases 

 protoplasm can be almost entirely dried up, but remains 

 capable of renewing its movement when again moistened. 

 Dilute salt solution and very dilute alkalies stimulate the 

 movements temporarily. Acids or strong alkalies per- 

 manently stop the movements ; ether, chloroform . . . 

 also stop it for a time. 



" Movement is suspended in an atmosphere of hydrogen 

 or carbonic acid, and resumed on the admission of air or 

 oxygen ; complete withdrawal of oxygen will after a 

 time kill protoplasm. 



" (3) ELECTRICAL. Weak currents stimulate the move- 

 ment, while strong currents cause the cells to assume a 

 spherical form and to become motionless." 



I will repeat, but paraphrase, the foregoing 



(1) Change of Temperature. Moderate heat acts as a 

 stimulant by lowering internal resistance. The movement 

 stops when the temperature is lowered near the freezing 

 point because of the enormous increase of internal resist- 

 ance so created, and as protoplasm dies at 45 C. (or 

 thereabouts), that temperature would naturally bring 

 about cessation of movement by killing the protoplasm. 



(2) Chemical Stimuli. Distilled water, regarded as a 

 foreign substance or fluid, may bring about a momentary 



