THE CONTRACTILE VACUOLE 4l7 



vacuoles and the simultaneous rupture of vacuole wall and papilla pul- 

 satoria represent sol-gel reversibility, it is obvious that exactly these 

 phenomena must be anticipated, on the basis of the concept of physiologi- 

 cal membranes such as described above. When two accessory vacuoles lie 

 touching each other, the cytoplasmic phase of the two-phase system is 

 pushed aside, at the same time removing the basic forces on which the 

 presence of these membranes depends. In the absence of these forces, 

 the membranes disintegrate at the site of contact, and the two vacuoles 

 fuse into one. Likewise, when the filled vacuole comes in contact with 

 the papilla pulsatoria, one phase (the cytoplasmic phase again) is pushed 

 aside, the membranes disintegrate at the site of contact, and the contents 

 of the vacuole are discharged to the exterior. After discharge the two- 

 phase system is again established, since there is cytoplasm on one side of 

 the pore (within the organism) and water on the other (outside the 

 organism), whereas prior to discharge there was water on the outside as 

 well as a fluid composed chiefly of water within the vacuole. The papilla 

 is formed in this manner from the vacuole wall, which readily accounts 

 for the similarity noted by Taylor. 



Other phenomena which can be explained in like manner by the pres- 

 ence of physiological membranes are easy to find in the Protozoa. The 

 ingestion of food by Amoeba is essentially the result of fusion of the 

 walls of the organism after they have been extruded around the food 

 particle in such a manner as completely to enclose it. The two-phase 

 system exists as long as there is water on one side of the cell membrane 

 and cytoplasm on the other; but when the engulfing process is complete 

 and cell membrane is in contact with cell membrane with no water 

 separating the two portions, the membrane disintegrates at the site of 

 contact, and continuity of cell structures as well as of the vacuole mem- 

 brane is established. The food-vacuole membrane persists as long as 

 there is water within to maintain the two-phase system. In a similar man- 

 ner one may explain the readiness with which an amputated fragment 

 of an amoeba unites with the parent body when the two portions come 

 together, although it has no bearing on the fact that a fragment from a 

 diverse strain is refused. It has also been observed that occasionally an 

 amoeba attempts to engulf a relatively large organism, such as P. cauda- 

 tuni, but is unable to accomplish this completely. The Paramechim is 

 squeezed in two, apparently, with half inside the amoeba and half out- 



