PHYSIOLOGY 119 



the pulsation of the contractile vacuoles of Paramecium caudatum in 

 fresh water as well as in salt water and obtained the following meas- 

 urements: 



The number of the contractile vacuoles present in a species is con- 

 stant under normal conditions. The contraction period varies from a 

 few seconds to several minutes in freshwater inhabitants, and is, as 

 a rule, considerably longer in marine Protozoa. Kitching (1938a) 

 estimated that a quantity of water equivalent to the body volume is 

 eliminated by freshwater Protozoa in four to 45 minutes and by 

 marine forms in about three to four hours. The size of contractile 

 vacuole in diastole may vary. Botsford (1926) reported that the con- 

 tractile vacuole in Amoeba proteus varied considerably within a short 

 period of time in size and rate of contraction under seemingly identi- 

 cal conditions. The rate of contraction is subject to change with the 

 temperature, physiological state of the organism, amount of food 

 substances, etc. For example, Rossbach noted in the three ciliates 

 listed below, the contraction was accelerated first rapidly and then 

 more slowly with rise of the temperature: 



Time in seconds between two systoles at 

 different temperature (C.) 



5° 10° 15° 20° 25° 30° 

 Euplotes char on 61 48 31 28 22 23 



Stylonychia pustulata 18 14 10-11 6-8 5-6 4 



Chilodonella cucidlulus 9 7 5 4 4 — 



How much water enters through the body surface of Protozoa is 

 not known, but it appears to be the major portion that is excreted 

 through contractile vacuoles. Water also enters the protozoan body 

 in food vacuoles. In Vampyrella lateritia which feeds on the cell con- 

 tents of Spirogyra in a single feeding, many contractile vacuoles ap- 

 pear within the cytoplasm and evacuate the Avater that has come in 

 with the food (Lloyd, 1926) and the members of Ophryoscolecidae 

 show an increased number and activity of contractile vacuoles while 

 feeding (MacLennan, 1933). The amount of water contained in food 

 vacuoles seems, however, to be far smaller than the amount evacu- 

 ated by contractile vacuoles (Gelei, 1925; Eisenberg, 1925). Other 

 evidences such as the contractile vacuole continues to pulsate when 

 cytosome-bearing Protozoa are not feeding and its occurrence in 

 automatons ciliates, would indicate also that the water entering 



