1923] Contractile Vacuoles in Amoebae 51 



Multiple Contractile Vacuoles 



In one experiment when Vahlkampfia calkensi were taken from 

 agar made up with sea water to agar made up with distilled water, 

 they developed two, three and even four vacuoles. These contracted 

 sometimes synchronously, sometimes at different rates. 



The presence of two or more contractile vacuoles seems to be quite 

 abnormal for amoebae. Hance (3) has noted the presence of multiple 

 contractile vacuoles in a certain line of Paramoecium caudatum, and 

 thinks it may be due to the fact that the paramoecium had been ex- 

 posed to high temperatures (40° C). In his experiments the extra 

 contractile vacuoles were passed on from generation to generation 

 with some variation in the inheritance. 



Calkins (4) suggests that an extra number of contractile vacuoles 

 may be due to a lowered vitality. This explanation seems applicable 

 to the case of Vahlkampfia calkensi which were certainly in a state of 

 lowered vitality as was shown by the fact that they were not repro- 

 ducing. The bacteria on which they lived multiplied very rapidly 

 and the amoebae were soon crowded out and died. 



Rate of Pulsation op Contractile Vacuoles 



It has been suggested by several investigators that the rate of pul- 

 sation of the contractile vacuole is probably influenced by the sur- 

 rounding medium. A good opportunity to study this offered itself at 

 Woods Hole when I was growing a Limax amoeba on media of differ- 

 ent densities to see what their effect w^ould be on its shape (Hogue 5). 

 Small pieces of agar containing amoebae were removed from the Petri 

 dish to a slide so that the amoebae were not disturbed and so as to be 

 able to study them with a higher magnification than was possible 

 when focusing through an inverted Petri dish. Ten successive read- 

 ings of the time of contraction of the vacuole in seconds were made 

 and the average calculated for each amoeba. These readings were 

 then averaged for the amoebae on each specific medium as shown in the 

 following table. 



