THE CELL AND PROTOPLASM 



The three concluding papers effectively 

 linked this Symposium with the National 

 Colloid Symposium which directly fol- 

 lowed. These include: "The Molecular 

 Structure of Protoplasm" by Sponsler, 

 "Protoplasm and Colloids" by Heilbrunn, 

 and "Structural Units" by Bernal. 



The general concept of the living cell as 

 an organized protoplasmic unit, which is 

 stressed in foregoing papers, evidently pre- 

 supposes for its protoplasm a fundamental 

 architecture, i.e., an integrated spatial 

 arrangement of the protoplasmic constitu- 

 ents. 



An analysis of this architecture is pre- 

 sented by Sponsler as based on the known 

 molecular constitution of protoplasm and 

 computed from fairly well-established di- 

 mensions of its protein chains and their 

 linkages through hydrogen bonds. Assum- 

 ing a degree of protoplasmic homogeneity, 

 it is concluded that the protoplasm com- 

 prises parallel protein chains, of dimen- 

 sions about 1000 A by 10 A by 4.5 A, which 

 are laterally united by water hydration 

 centers, and which in turn compose a 

 sponge-like framework intercalated with 

 water containing the various solutes. From 

 this elementary protoplasmic architecture 

 is derived the fundamental pattern of the 

 primordial cell which, through develop- 

 mental differentiation, gives rise to the 

 tissue cells and organs of the adult organ- 

 ism, as recounted in the earlier discussions. 



The colloidal properties of protoplasm 

 and its cellular differentiation are vari- 

 ously exemplified in the paper by Heil- 

 brunn. His recent investigations have 

 demonstrated especially a localization of 

 calcium in the cortex of the cell which, 

 upon appropriate stimulus, is released 

 within and so effects a gelation of the pro- 



toplasm involving contraction. Further 

 evidences of this gelating effect were found 

 upon exposing cut surfaces of cells to vari- 

 ous concentrations of calcium salts. There- 

 upon a reversible limiting membrane was 

 formed on the cut surface, or a bulb-like 

 contraction was locally induced, due to the 

 penetrated calcium. Thus the age-old 

 problem of contractility, a common prop- 

 erty of protoplasm, may find its solution 

 normally in the localization and release of 

 calcium in the cell's cortex. 



Recalling the emphasis given throughout 

 the Symposium to the structural aspects of 

 protoplasm, Bernal in the final paper urges 

 that consideration of the energy relations 

 is equally important since not only do the 

 energies involved determine the sort of 

 structure possible, but also their nature 

 must be known in order to account for that 

 structure. These energies relate primarily 

 to the protein constituents of the proto- 

 plasm, a model for which may be found in 

 the tobacco mosaic virus when contained in 

 known salt solutions. Here the virus enti- 

 ties, which are long protein molecules, be- 

 come oriented in striking spindle-like pat- 

 terns, or tactoids, and their regular dis- 

 tances apart vary directly with the concen- 

 tration of the salt solution. Evidently 

 long-range forces between the virus entities 

 are operative through the ionic atmosphere 

 of the surrounding medium with which 

 the former are in equilibrium. The magni- 

 tude and direction of forces inside the tac- 

 toid pattern are different from those on the 

 outside. These differences, in fact, account 

 for the pattern formation. Apparently 

 analogous forces may similarly account for 

 the formation of the mitotic figure and the 

 ensuing phenomena during the mitosis of 

 the living cell. 



