PARAMECIUM 133 



is carried by a streaming of the endoplasm around 

 the body, passing first backward along the ventral side, 

 then forward nearly to the middle of the body, then 

 through several turns of a short circuit in this region of 

 the body, and finally forward to the front end and back 

 so as to complete the circuit of the body. During these 

 wanderings the food is digested. The undigested remains 

 are then expelled at a spot just behind the end of the 

 gullet, where a passage through the ectoplasm, known as the 

 temporary anus, is formed when it is required. Two periods 

 may be recognised in the digestion. In the first period 

 the water taken in with the food is being absorbed. 

 Substances are secreted into the vacuole during this period 

 which give it an acid reaction and kill the prey. In the 



second period an alkaline 

 ' ; & ». c. digestive juice is secreted 



into the vacuole, which 

 increases in size. It 

 appears that Paramecium 

 cannot digest fat. 

 Fig. 82.— A diagram of the course of Like all other organ- 

 elle circulation of the food vacuoles isms, Para- 

 in Paramecium. Stimuli?* mecium is 

 I.e., Long circuit ; s.c, short circuit. automatic 



(p. 12). Its incessant 

 activity is spontaneous so far as immediate external stimuli 

 are concerned, but is continually modified by such stimuli. 

 The movements of Paramecium are much more active and 

 definite than those of Amoeba, and it is correspondingly 

 easier to observe the effect of various stimuli upon the 

 animal. These effects are of two kinds, upon the rate 

 of movement and upon its direction. (1) Many acids, 

 alkalies, salts, and other substances in dilute solutions 

 cause an increase in the rate of motion owing to a more 

 rapid working of the cilia. Moderate increase of tempera- 

 ture has the same effect. On the other hand, dilute 

 solutions of narcotics, such as alcohol, ether, or chloroform, 

 cause the cilia to work more slowly. All these reactions 

 are probably merely the direct effects which such stimuli 

 are known to have upon protoplasm. (2) In order that the 

 effect of stimuli upon the direction of movement may be 



