PHYSIOLOGY 99 



That the ehmination of excess amount of water from the body 

 is one of the functions of the contractile vacuole appears to be 

 beyond doubt judging from the observations of Zuelzer (1907), 

 Finley (1930) and others, on Amoeba verrucosa which lost gradu- 

 ally its contractile vacuole as sodium chloride was added to the 

 water, losing the organella completely in the seawater concentra- 

 tion. Herf (1922) studied the pulsation of the contractile vacuoles 

 of Paramecium caudatum in fresh water as well as various salt 

 concentrations, and obtained the following measurements : 



Per cent NaCl in water . 25 0.5 . 75 1 . 00 

 Contraction period in 



second 6.2 9.3 18.4 24.8 163.0 

 Excretion per hour in 



body volumes 4.8 2.82 1.38 1.08 0.16 



The contractile vacuole also serves to remove from the body 

 part of soluble catabolic wastes, judged by numerous observa- 

 tions. Weatherby (1929) showed that the contractile vacuoles of 

 Paramecium and Spirostomum contain urea, and that of Didini- 

 um contains ammonia and occasionally trace of uric acid. The 

 number of the contractile vacuoles present in a given species as in 

 various species of Paramecium, is not always constant. Nor is its 

 size constant. According to Taylor (1920) the average size of the 

 contractile vacuole of Euplotes patella is 29/i at maximum dias- 

 tole, but may become 45-50^ in diameter upon disturbance or 

 after incision. The rate of pulsation is subject to changes with 

 temperature, physiological state of the organism, amount of food 

 substances present in the water, etc. For example, Rossbach ob- 

 served in the three ciliates mentioned below that the pulsation of 

 the contractile vacuole increased first rapidly and then more 

 slowly with the rise of the temperature of the water: 



Time in seconds between two systoles at 



Euplotes char on 

 Stylonychia pustulata 

 Chilodonella cuculhdus 



Aside from the soluble forms, there often occur in the protozoan 

 body insoluble catabolic products in the forms of crystals and 

 granules of various kinds. Schewiakoff (1893) first noticed that 

 Paramecium often contains crystals (Fig. 39) composed of calcium 



