MAGNETIC CONTROL OF GEOTROPISM IN 

 PARAMOECIUM 



E. H. HARPER 



From the Zoological Laboratory of Northwestern University 



In a preliminary paper the writer showed that cultures of 

 Paramoecium caudatum which have ingested iron particles show 

 an increased negative geotropic response for a temporary period. 

 It was observed that the particles are at first lodged in the 

 posterior end, and that the changed response is coincident with 

 this condition and tends to disappear as the particles become 

 more evenly distributed through the endoplasm. In an animal 

 so loaded the posterior end tends to sink more rapidly so as 

 to cause it to assume an upward orientation, provided that it 

 is moving in a narrow spiral or nearly straight path, i. e., in the 

 absence of any marked deflections of the anterior end such as 

 occur when the animal is stimulated. This is readily observed, 

 particularly in individuals which start to move in a horizontal 

 direction. The action is to be interpreted as a passive orienta- 

 tion to gravity not involving response to a stimulus. 



This result naturally suggests the possibility of experimenting 

 with the magnetic control of the movements of Paramoecia 

 containing iron. In this paper follow some experiments with 

 the combined effects of gravity and magnetism. 



APPARATUS AND METHODS 



An electro-magnet was employed wrapped for a length of 

 27.5 cm. with seven turns of wire, 57 turns to the cm. The core 

 was of ten pieces of a diam. of. 4.5 mm., 31 cm. in length. An 

 alternating current from the lighting circuit was used, which 

 was passed through a 50 w. incandescent lamp in series. A 

 direct battery current was also tried for comparison, but its use 

 gave no different results. 



A half -gram or so of iron by alcohol is rubbed up fine in an 

 agate mortar with a few drops of water. From 1-2 cc. of water 

 containing a dense culture of Paramoecia, free from sediment, 

 is added and the iron kept in suspension by drawing the water in 



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