Pulsating vacuoles

Fig. 2 Electron micrograph of N. ovalis (a) with a hydrogenosome (b). The scale bar in (a) represents 10 micrometers, the scale bar in (b) represents 0.5 micrometers. H hydrogeno-somes, Ma macronucleus, Mi micronucleus, Cs cytostome, PV pulsating vacuole...

Contractile Vacuole (pulsating vacuole) A vesicular reservoir in protozoa in which water and waste products collect and are discharged to the outside by means of a contraction of the vacuole. 

Pulsating vacuoles are also observed in the complex coacervate gelatin — gum arabic if small drops are subjected to a d.c. electric field In this case also the drop is smaller than the original one after a pulsation. 

Many cells of the tissue have been injured whereby the gum arabic has wholly or largely left them. Only three cells have not been injured and have accumulated toluidine blue to a maximum extent, a Initial state the toluidine blue arabinate coacervate is on the wall. The white streaks and spots in these cells are places where because of folds in the celloidin membrane the coacervate on the wall is very thin and thereby transparent, b and c successive stages of the change in the wetting caused by treatment with 5 m. eq. per I NaCl. Pulsating vacuoles are formed in the coacervate drops in c. d In a later stage and after application of a direct current field (anode on the left, cathode on the right) see text. 

The phenomenon of pulsating vacuoles which accompanies the dissolving of the coacervate drops (Fig. 43c), seems also to be related to the negativation of the coacervate. Such a negativation also occurs under the circumstances described in 4 a (p. 454, contact of the coacervate drops with excess of gum arabic sol). 

At a certain instant the coacervate shell bursts and changes into a coacervate drop which is smaller than the original one. This can again swell up with the formation of a vacuole and then burst once more. As a rule there is then not enough coacervate over for the whole phenomenon to repreat itself so that the pulsating system is already ruined after a few pulsations (compare also Fig. 43 c, p. 476). 

Here we encounter again a similar case to that above with gum arabic + toluidine blue since here also under conditions in which the coacervate will go wholly or partially into solution (in the former case by a change of the mixing ratio colloid anion / dye cation, in the present case by the action of the added salt) a large central vacuole is formed. A point of difference is merely that the vacuole does not break through in the present case and thus no pulsation phenomena occur, at least when one chooses the salt concentration so that the complex coacervate just does not go entirely into solution. 

The central vacuole is here produced (see Fig. 236—d) by the coalescence of a number of primarily formed smaller ones, whereby the abnormal feature does not lie in the vacuolation itself but rather in the succeeding enlargement of the primary vacuoles and the peculiar contradiction which exists between the coalescence of these vacuoles among themselves and the absence of withdrawal of these vacuoles, or of the central vacuole formed from them, from the drop. This does not occur even after a fairly long time so that the pulsation phenomenon, which we discussed in 4 a, (p. 454) above, is absent here. 

Yet the most striking difference is that there the withdrawal of the central vacuole is a sudden happening which rightly deserves the name pulsation, here however it is a very slowly evolving process whereby it is possible to follow the path followed morphologically in the withdrawal. 

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