PROTOPLASM OF PROTOZOA 65 



2oa possess an interesting mechanism for controlling their osmotic state. 

 The protoplasm of these organisms possesses a much higher osmotic 

 concentration than that of the surrounding medium. For this reason 

 water tends continually to enter them, and, were it not for the controlling 

 mechanism of the surface membrane and the continuous bailing out 

 process of the contractile vacuole, the animals would swell up and burst. 

 Adolph ( 1931 ) has reviewed the literature dealing with the rate of water 

 exchange in Protozoa and has found that the fastest turnover is in 

 CryptochUum, which excretes its body volume in 2 minutes; the slowest 

 water exchange was in Amoeba, which requires 31.5 hours, while P. 

 caudatum eliminates its own body volume of water in from 15 to 

 20 minutes. 



Water, when injected in small amounts into an amoeba, readily dif- 

 fuses throughout the cytoplasm, causing a temporary cessation of ame- 

 boid movement (Chambers, 1924). However, if the injection be great 

 in amount i.e., equal to half the body volume, the water tends to collect 

 on one side in the form of a large blister, which is eventually pinched off, 

 and within a short time the amoeba resumes its normal activities (How- 

 land and Pollack, 1927). In addition, a marked increase in contraction 

 rate and water output of the contractile vacuole was noticed. 



In contrast to the above experiment. Mast and Doyle (1934) caused 

 A. proteus, A. duhia, A. radio sa, and A. dofleini to lose water by plac- 

 ing them in 3-percent egg albumen, hypertonic salt solutions, or solutions 

 of calcium gluconate. The organisms decreased in size and their surfaces 

 became wrinkled and covered with protuberances, folds, and crevices. 

 The crests of some of the adjoining protuberances and folds fuse, giv- 

 ing rise to tubes open at one end. The region of the fused folds push 

 out, forming a pseudopodium, thus extending the tubule, the mouth of 

 which was observed to expand and contract, drawing the fluid in. Later 

 the tubule disintegrates, releasing the fluid to the inside of the organ- 

 ism. This "drinking" of water by means of tubules seems to be an im- 

 portant mechanism, to compensate for the rapid loss of water in the 

 organism. Further experiments by Mast and Fowler (1935) showed that 

 when A. proteus was placed in Ringer solution containing various con- 

 centrations of lactose, it would decrease as much as 88 percent in total 

 volume without injury. The rate at which the water leaves the cell was 



