BEHAVIOR OF METR1DIUM. 4! 



accept filter paper (in some cases plain, in others soaked in meat 

 juice). After this first test, the same region of the disk was fed 

 successive pieces of meat, which were all readily taken. After 

 eight to twelve pieces of meat had been accepted, a piece of filter 

 paper like that originally accepted was given to the same region 

 of the disk. // tvas not accepted. This experiment was repeated 

 with many specimens, always with the same result. This result 

 was likewise reached if the animal was not allowed to complete 

 the swallowing of the meat, the latter being removed after it had 

 passed into the oesophagus. This, of course, shows conclusively 

 that loss of hunger is not the cause of the change of reaction 

 toward the paper. 



The placing of meat juice on a certain region of the disk 

 causes the food reaction, as Parker has shown. If this experi- 

 ment is tried successively a dozen times in the same region of the 

 disk, the animal comes to reject filter paper in this region, as in 

 the experiments described in the foregoing paragraph. 



Thus it is not necessary that weak stimuli should be repeated 

 in order that the animal shall reach a state in which it fails to 

 react to them. Repetition of strong stimuli (meat) causes failure 

 to react to weak stimuli just as readily as does repetition of the 

 latter. Repetition of strong stimuli alone, of weak stimuli alone, 

 and of the two in alternation, all have the same effect ; the animal 

 ceases to react to weak stimuli. 



In all cases in which meat is fed to a given region, moreover, 

 the reaction to strong stimuli ceases some time later than that to 

 weak stimuli. After giving a certain region sixteen to twenty 

 pieces of meat, meat is no longer accepted here, though other 

 regions of the disk take it readily. 



4. Fatigue. The facts brought out in the foregoing para- 

 graphs seem to make possible a clear interpretation of the rejec- 

 tion of the paper. It is evidently a case of plain fatigue. After 

 stimulating a certain region of the disk a number of times, it 

 ceases to react first to weak stimuli, then to strong stimuli - 

 though other parts react as before. The same results are pro- 

 duced whether the successive stimuli are all strong or all weak, 

 or partly strong and partly weak. It appears evident therefore 

 that it is the reaction of the animal, not the precise character of 



