Water 43 



pulsation of the c. vacuoles in very dilute sea water. In concentrations higher 

 than 12 per cent sea water all pulsations stopped.'-'^ Euplutes patella kept 

 in 65 per cent sea water often contained a large vacuole which did not con- 

 tract. 25^ 



More adaptation experiments have been carried out with Paramecium 

 caiidatum than with any other species. When Paramecium is lirst put into a 

 hypertonic solution the body becomes flattened as water is withdrawn but 

 later recovers its normal shape."' ^-^' In increased external concentrations 

 the amount of fluid expelled by the contractile vacuoles decreases."''- '*■'■ ^-" 

 In Paramecium caudatum 1"^ the vacuolar excretion of fluid decreased in 

 salt solutions of increasing concentrations as follows: 



Vacuolar o^itpiit of 



fluid in equivalents Per cent NaCl 



of body volume per hour solutio7i 



4.8 



1.38 0.5 



1.08 0.75 



0.16 1.0 



Cultures of Paramecium xvoodruffi and Paramecium calkinsi were established 

 in several dilutions of sea water. ''^ After 5 months the average intervals 

 between pulsations of the c. vacuoles in P. woodruffi were 13 seconds in fresh 

 water, 22 seconds in 25 per cent sea water, 32 seconds in 50 per cent sea water, 

 47 seconds in 75 per cent sea water, and 65 seconds in 100 per cent sea water. 

 P. calkinsi showed an average interval of 23 seconds at all concentrations. 

 Paramecium ca^^datum acclimated much less readily to sea water, although 

 Frisch "^ did culture it in 5 per cent sea water and allowed the water to evap- 

 orate so that in 24 to 42 days the culture medium was equivalent to 40 per 

 cent sea water. The intervals between pulsations of the c. vacuoles lengthened 

 from 1 1 seconds to 89 seconds, although some recovery of rate occurred later 

 in the 40 per cent sea water. There may be specific salt effects in addition to 

 tonicity. For example, in Paramecium caudatum '^^' in glucose solution of 

 Af.p.=0.075 the c. vacuole pulsated at 2.4— 4.1/min., whereas in Ringer solu- 

 tion of the same osmotic concentration the rate was 3.8-4.7/1 min. and in 

 CaCl2 of the same osmotic concentration it was 4.2-7.2/min. Differences be- 

 tween pulsation rate in isosmotic NaCl and glycerol are reported for Glaucoma 

 colpoda (Degen, quoted by Metzner''")- It appears, therefore, that the c. 

 vacuoles of Protozoa have an osmoregulating function but that other factors 

 besides tonicity of the external medium may affect the amount of fluid ex- 

 creted. In marine Protozoa c. vacuoles eliminate water taken in with food and 

 may eliminate ions. 



Avenues of Water Entrance. Three routes of entrance for water have been 

 described: (1) across the body surface, (2) with food, and (3) through the 

 cytopharynx membrane. All water must enter through the body surface in 

 nonfeeding rhizopods and in mouthless parasitic ciliates (some of the Opalini- 

 dae). The values given previously for vacuolar output in different media 

 are largely nonfeeding determinations. The permeabiHty to water as given 

 above is great enough that if the cells in fresh water had no vacuoles they 

 could not survive long. For example, Pelomyxa carolinensis kept without 

 food decreases about 8 per cent in volume every 24 hours for 3 days-" 



