72 GENERAL BIOLOGY 



of a circuitous course in avoidance of an obstruction, 

 etc., indicate this, and since there is only protoplasm present 

 and responsible for the actions, it follows that sensibility, 

 or at least, the capacity for responding to external stimuli, 

 is another property of protoplasm. We tap the slide 

 sharply and the amoebas contract, drawing in their pseudo- 

 podia, but soon, after a different interval in different indi- 

 viduals, they resume activity again. 



The larger amoebas live in the sediment on the bottom of 

 ponds and ditches, in the slime on the submerged leaves of 

 aquatic plants, etc., and while much more difficult to obtain 

 in sufficient numbers for class use, they are, on account of 

 their size, much more favorable for studies of some of the 

 phenomena outlined above. One gets specimens for study 

 by mounting the slime upon a slide and searching till 

 amoebas are found. Since these commonly devour diatoms 

 and desmids, which show their characteristic colors for a 

 time after being engulfed, the process of digestion (as ev- 

 idenced by the disappearance of the normal plant structures) 

 is in these species more easily observed. 



Study 10. The structure and activities of Paramoecium. 

 Materials needed: A hay infusion a week or more old 

 in which the surface layer of the bacterial jelly is breaking 

 up, being largely consumed, and in which Paramoecium has 

 appeared in large numbers : or, an old infusion that has 

 been kept going by occasional feeding with corn meal. The 

 paramoecia will be found about the edges of the culture 

 close to the surface. They are large enough to be seen as 

 minute oblong white specks in rapid motion. They must 

 be present in sufficient numbers for one to get a number 

 in a drop of water taken up by a pipette, and if not so 

 numerous, they should be concentrated, by some such sort 

 of filtering apparatus as that described in the appendix. 

 There will be needed also, besides the usual labora- 



