GEOTROPISM OF PARAMECIUM AND SPIROSTOMUM. II 



plasm" (4, p. 181). The writer continued his observations for 

 about three hours and found that no such change in reaction 

 occurred. At the end of the time, almost all the animals in his 

 case were at the top of the tubes. 



About 1 6 hours later, in the treated tubes, all the paramecia 

 were dead except a few in tubes a and b. They may have died 

 earlier than this, as the writer did not have a chance to observe 

 them in the meantime. He examined the dead animals under 

 a microscope, but the iron particles were not noticeably "dis- 

 tributed through the endoplasm"; some animals were found 

 vacuolated and many must have broken into pieces, because few 

 dead animals were found. On comparing the above observations 

 w r ith Harper's, we find some differences. According to Harper, 

 'the paramecia rid themselves of the iron after the course of 

 a few hours without apparently harmful effects from a small 

 amount" (3, p. 995). It may be premature to assume a chemical 

 effect on the protoplasm of the iron-ingested paramecia, but we 

 may expect some abnormal reactions of the animals, besides the 

 purely physical; because we saw that all the paramecia treated 

 for 3.5, 5, and 10 minutes died within at least 16 hours, as already 

 stated. In other words, the more iron the animals ingested the 

 quicker their death resulted. 



From the above results it is clear that the iron-ingested para- 

 mecia are more apt to be negatively geotropic than the normal 

 ones, as Harper has shown. Since the iron is ingested in the 

 posterior region, which presumably is thus made heavier than 

 the anterior region, Harper's view r of a "passive orientation" 

 may be true in this particular case. The writer does not mean, 

 however, by "passive orientation," as Harper does, that the 

 "pull of gravity' "is too weak to stimulate" in any case. In 

 point of fact, the normal Paramecium orients its anterior end 

 upward not because that end is heavier but in spite of it. Of 

 course, therefore, when the posterior end is rendered heavy by 

 iron the orientation is easier. It is here that the "mechanical 

 theory" deserves some credit. It gives us one of the factors of 

 orientation of some animals like iron-ingested paramecia 

 against the force of gravity. The "stern-heaviness" or "bow- 

 heaviness, " therefore, may be one of the conditions of stimulation 



