Decembeb 27, 1895.] 



SCIENCE. 



897 



ules occur as a rule only at the nodal points 

 of the net, since when lamp-black is added to 

 foam drops it collects at the nodes between the 

 vesicles. The striated appearances of gland 

 cells seem to indicate a fluid state and the oc- 

 currence of difiusion currents. Likewise the 

 radiating appearances seen in dividing cells and 

 caused by rows of meshes (alveoli) are like the 

 lines seen in artificial foams and caused, ap- 

 parently, by diffusion currents. So much do 

 some of these striations resemble those of the 

 artificial foam that Prof. Butschli is led to 

 assign diffusion currents as their cause in the 

 case of the striations about the contractile vac- 

 uole of an amoeba during diastole, and of the 

 suns at the poles of the spindle in caryokinesis. 

 The striated appearances in pseudopodia and in 

 strands of streaming protoplasm in plant cells 

 are due to rows of elongated meshes (alveoli), 

 and may be taken as evidence of the fluid 

 nature of the protoplasm since they appear to be 

 rows of vesicles stretched by tension. Similar 

 appearances in nerve fibers offer an obstacle to 

 the idea of the fluid state of protoplasm, for Ave 

 here have permanently elongated meshes with- 

 out apparent tension ; if their elongation were 

 caused by stretching in growth we would yet 

 have to grant considerable rigidity in the 

 lamellse or material of the net. 



Before considering the movements of foams 

 and of protoplasm we may point out the rela- 

 tionship of the foam theory to those cases of 

 apparently structureless protoplasm that re- 

 main for any theory to resolve after the actual 

 observations have reached their limit. In the 

 pseu-dopodia of Gromia and in the ectosarc of 

 Rhizopods there are clear areas of protoplasm 

 without granules, network or other discovered 

 structure. Such apparently structureless pro- 

 toplasm has been variously interpreted: By 

 Heitzmann as regions where the meshwork is 

 so stretched and attenuated as to be invisible; 

 by Frommann as regions in which the network 

 has become dissolved in the matrix; by Flem- 

 ming as due to crowding of filaments to the 

 point of indistinguishability, and by Lej'dig as 

 masses of the hyaloplasm crept out from the 

 framework of spongioplasm. On Biitschli's 

 theory such areas appear structureless because 

 the alveoli are widened with walls so stretched 



as to be invisible. The thinness of the walls 

 would make the mass physically more like a 

 solid, and, as a matter of fact, we find such 

 homogeneous protoplasm more rigid or viscid 

 than the distinctly reticular internal pai'ts in 

 rhizopods. 



Coming now to the movements of artificial 

 foams as bearing upon the probable structure of 

 protoplasm we find that such foam drops may, 

 under favorable conditions, exhibit movements 

 from place to place, changes in outline and cer- 

 tain internal currents. 



The change of place may be in an extreme 

 case as much as .45 mm. in a minute. The change 

 of form consist in outpushings here and there 

 that give the drop a decidedly amoeboid outline 

 that changes considerably in a few minutes' time. 

 Of the internal currents the most interesting are 

 the so-called ' extension currents ' that pass out 

 from the interior towards the surface, spread 

 out over the surface and tend to return towards 

 the point of origin. In a smaU drop there may 

 be thus an axial current moving towards one 

 end, which will be the anterior in progression, 

 while at the other end there is a dead region 

 where particles of India ink, if added to the 

 foam, tend to collect in a stationary state. Such 

 an extension current may die out and be suc- 

 ceeded by another with a different axis. Two 

 drops may run together and acquire a new 

 center of extension currents. In large drops 

 there may be several centers of extension cur- 

 rents and each runs out into a pseudopodium- 

 like outpushing of the mass. As one center of 

 streaming dies down and another appears the 

 outline of the large drop changes as above men- 

 tioned. 



Such streaming currents may continue to ex- 

 hibit themselves for a daj^, in one case for as 

 many as six days. The currents are more active 

 when the drop is heated, and electric shocks 

 may cause change in the direction of movement, 

 wrinkling of the surface and bursting of vesicles 

 in the interior. 



The probable explanation of these movements 

 of the artificial foam is to be sought in the 

 phenomena of ' superficial extension currents ' 

 that are generated whenever the surface tension 

 of a liquid in air or in another liquid is locally 

 diminished by bringing a spot on its surface in- 



