102 



SCIENCE 



[N. S. Vol. XXXIV. No. ! 



surface layer in greater concentration than 

 in the interior. Now in such a system as 

 we have imagined protoplasm to be, the 

 sum of the areas of the surfaces of all the 

 phases must be very great, and conse- 

 quently the concentration of the various 

 substances distributed through it must 

 vary greatly, not merely according as they 

 are distributed in one or the other phase, 

 but also as they are concentrated still more 

 at the surfaces of one or the other of the 

 phases. This concentration at surfaces 

 may be very great so that the substances 

 are present as though under great pres- 

 sure, and we must imagine that reactions 

 are facilitated at surfaces just as reactions 

 with gases are facilitated by high pres- 

 sures. Finally, we can imagine reactions 

 facilitated whenever conditions arise which 

 diminish surface energy, for in that case 

 free energy is produced in the narrow con- 

 centrated surface film, How this might 

 facilitate reactions we can only con.jecture. 

 So far we have considered only the 

 grosser phases. Finer phases, however, 

 exist in protoplasm. It is now pretty well 

 established that colloidal solutions are mul- 

 tiple-phase systems. Cells contain colloids 

 in solution, and these colloids usually are 

 of the type known as emulsion colloids, 

 which means that all the phases of the col- 

 loidal solution are fluid. We have then 

 here phases of very minute dimension. 

 Now it is well known that the energy act- 

 ing at surfaces increases relatively with 

 the increase in curvature of the surface. 

 The curvature of these minute colloidal 

 phases is very great, and the energy which 

 Hcts in these infinitely curved surfaces is 

 correspondingly powerful. It is quite pos- 

 sible that many of the phenomena which 

 are termed enzymotic are brought about 

 by forces of this type, for it is very prob- 

 able that the class of agents termed en- 

 zymes is not a uniform one, but includes 



many classes of quite difi^erent agents act- 

 ing by as many different mechanisms. 



We have seen how considerations of 

 structure have led to conceptions of cell 

 dynamics. Conversely, a consideration of 

 these dynamics can lead us back to a 

 deeper understanding of structure. 



Protoplasm ordinarily contains 80 per 

 cent., and upwards, of water. Some beings 

 may contain even more. For example, the 

 medusfe or jelly-fish, fairly firm structures 

 though they are, contain but 3.7-4.6 per 

 cent, of solids." Of these solids over 3 per 

 cent, are the sea salts, so that the bell of 

 the medusa, as solid as a firm jelly, can 

 almost be said to consist of organized sea- 

 water. Ordinary protoplasm is not as 

 thin as this. Still of its 15 or 20 per cent, 

 of solids a considerable portion is inorganic 

 salts and other electrolytes, for the greater 

 part in solution, so that they hardly pro- 

 duce solidity. The remaining substances 

 consist of fats, proteins, lipoids and other 

 colloidal material. Built of such materials, 

 it is hard to see how an organism can have 

 so nearly solid or rather semi-solid a struc- 

 ture as protoplasm. If, however, we im- 

 agine the materials of which protoplasm is 

 composed as distributed in different phases, 

 the difficulties are not so great. If we 

 imagine the fat and the lipoid as present i-n 

 a different phase from the water, being 

 present as an emulsion, perhaps rendered 

 permanent by some such substance as soap, 

 and if we think of other substances such as 

 the proteins present in a colloidal and vis- 

 cous state, and, if we imagine both the 

 crystalloids and the colloids distributed 

 between the various phases, we can get a 

 structure which will be as firm as proto- 

 plasm is known to be. Thus it is easy to 

 take egg-albumen, oil and sugar solution 

 and mix them so thoroughly that the re- 



° Krukenberg, ' ' tJeber den Wassergelialt der 

 Medusen," Zool. Ameiger, 1880, S. 306. 



