388 THE FORMS OF CELLS [ch. 



dilute glycerine), the cell-sap tends to diffuse outwards, the proto- 

 plasm parts company with its surrounding and supporting wall, and 

 then hes free as a protoplasmic cylinder in the interior of the cell. 

 Thereupon it soon shews signs of instability, and commences to 

 disrupt; it tends to gather into spheres, which however, as in our 

 illustration, may be prevented by their narrow quarters from 

 assuming the complete spherical form; and in between these 

 spheres, we have more or less regularly alternate ones, of smaller 

 size*. We could not wish for a better or a simpler proof of the 

 essential fluidity of the protoplasm f. Similar, but less regular, 

 beads or droplets may be caused to appear, under stimulation by an 

 alternating current, in. the protoplasmic threads within the living 

 cells of the hairs of Tradescantia; the explanation usually given is, 

 that the viscosity of the protoplasm is reduced, or its fluidity 

 increased ; but an increase of the surface-tension would seem a more 

 likely reason}. 



In one of Robert Chambers's delicate experiments, a filament of 

 protoplasm is drawn off, by a micro-needle, from the fluid surface 

 of a starfish-egg. If drawn too far it breaks, and part returns within 

 the protoplasm while the other rounds itself off on the needle's 

 point. If drawn out less far, it looks hke a row of beads or chain 

 of droplets; if yet more relaxed, the droplets begin to fuse until 

 the whole filament is withdrawn; if drawn out anew the process 

 repeats itself. The whole story is a perfect description of the 

 behaviour of a fltiid jet or cy finder, of varying length and 

 thickness §. 



We may take note here of a remarkable series of phenomena, 

 which, though they seem at first sight to be of a very different order, 



* The intermediate spherules appear with great regularity and beauty whenever 

 a liquid jet breaks up into drops. So a bursting soap-bubble scatters a shower 

 of droplets all around, sometimes all alike, but often with a beautiful alternation 

 of great and small. How the breaking up of thread or jet into drops may be helped, 

 regularised, and sometimes complicated, by external vibrations is another and by 

 no means unimportant story. 



t Though doubtless to speak of the viscid thread as a fluid is but a first approxi- 

 mation; cf. Larmor, in Nature, July 11, 1936. 



X Kiihne, Untersuchungen ilber das Protoplasma, 1864, p. 75, etc. 



§ Cf. R. Chambers in Colloid Chemistry, theoretical and applied, ii, cap. 24, 1928; 

 also Ann. de Physiol, vi, p. 234, 1930; etc. 



