OSMOTIC GROWTH 127 



stains used for microscopy, in the liquids used for fixing pre- 

 parations. 



We now know that the physical force which builds up these 

 growths is that of osmotic pressure, since the slightest considera- 

 tion 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 milli- 

 metres 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 

 obstinatelv downwards once more, in opposition to the hydro- 

 static 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 Cad., in a shallow Hat- 

 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 



