Precipitated osmotic membranes are very widely distributed in nature. Professor Ulenhuth has seen iron growths in alkaline sodium hypochlorite (Javelle water), and Lecha-Marzo has demonstrated the osmotic growth of the various
stains used for microscopy, in the liquids used for fixing preparations.
(a) The sickle-shaped growth.
(b) The growth broken by the upward pressure of the solution.
(c) The wound having cicatrized, the stem continues to grow downwards.
We now know that the physical force which builds up these growths is that of osmotic pressure, since the slightest consideration will show the inadequacy of the usual explanation that the growth is due to mere differences of density, or to amorphous precipitation around bubbles of gas. These may indeed affect the phenomenon, but can in no way be regarded as its cause.
One of our experiments throws considerable light on this question. In a glass vessel we placed a concentrated solution of carbonate of potassium, to which had been added 4 per cent. of a saturated solution of tribasic potassium phosphate. Into this solution we dropped a fragment of fused calcium chloride, and obtained a vermiform growth some 6 millimetres in diameter. This growth was curved, at first growing upwards, then for a short distance horizontally, and finally downwards. The upward pressure of the solution, which was heavier than the growth, ultimately broke it at the top of the curve, as shown at b, Fig. 37. The liquid contents of the growth began to ooze out through the wound, but this after a time became cicatrized, and the stem continued to grow obstinately downwards once more, in opposition to the hydrostatic pressure. In consequence of this pressure the growth is sinuous, tacking as it were from side to side like a boat against the wind. We give three successive photographs of this growth, which attained a length of over 10 inches. We have frequently obtained these vermiform growths forming a series of such loops, growing upwards and falling again many times in succession.
Osmotic Growths in Air.—Certain of these artificial cells may be made to grow out of the solution into the air. For this purpose we place a fragment of CaCl2 in a shallow flat-bottomed glass dish, just covering the fragment with liquid. The best solution is as follows:—
| Potassium carbonate, saturated solution | 76 parts. |
| Sodium sulphate, saturated solution | 20 ,, |
| Tribasic potassium phosphate, saturated solution | 4 ,, |