186 



THE CELL AND PROTOPLASM 



enlarged faces. If, on the other hand, 

 random association is the rule, then the 

 faces of the large aggregate present mosaic 

 l^atterns in which all the three faces of the 

 super-molecule may appear. Of this form 

 of aggregate, then, there are man}- sizes, 

 and it is likely that these, for the most part, 

 produce the specks of light in the ultra- 

 microscope; and perhaps they may also be 

 responsible for the protein X-ray diffraction 

 rings which we obtained from the sediment 

 of various protoplasmic materials. 



The third form, the loose aggregate, is a 

 much less concentrated particle and really 

 is not a particle at all in the sense of the 

 first two forms, for it is merely a spongy 

 collection consisting of super-molecules and 

 compact aggregates with interpenetrating 

 water channels. This sponge also may 

 occur in many sizes up to visibility. It is 

 not at all a rigid structure ; the components 

 might readily have sufficient thermal move- 

 ment to produce the "shimmering haze" 

 which Bayliss describes as seen in the ultra- 

 microscope. Aggregates of this type, both 

 small and large, may have the inherent or- 

 ganization which biologists demand, and 

 still exist in a particulate state which would 

 permit the streaming of protoplasm or, on 

 the other hand, would permit the whole cell 

 or any part of it to become a gel, as con- 

 ditions might demand. 



The i^roperties of such particles, it seems 

 to me, with only slight modifications would 

 be extremely versatile in the formation or 

 organization of molecular mechanisms, or 

 the "wheels" of Szent-Gyorgi 's discussion. 

 The versatility would result from the varied 

 types of surface mosaics of its denser com- 

 ponents; and the positions taken by these 

 particles within the sponge or net could 

 serve to hold enzyme systems in close prox- 

 imity, as, may be needed, for example, in the 

 respiration system described by Theorell. 



This, pei-liaps, is sufficient belaboring of 

 this three-dimensional network of siibmicro- 

 scopie particles consisting of two inter- 

 penetrating systems, one of water and small 

 dissolved molecules, and one mostly of ])ro- 

 teins. It may be worth while to summarize 

 briefly to see how much is speculation and 



how much has an experimental basis. The 

 weakest point is that which we have met 

 in almost every paper of this series ; that is, 

 our lack of well-defined knowledge of the 

 proteins. We have carried what little 

 knowledge we have from the molecular 

 range up into the range beyond reach of 

 most of our methods, and have deliberately 

 transplanted conceptions of atomic and 

 molecular structures into the field just be- 

 low visibility, where we have used them to 

 construct what might simulate replicas of 

 particles which we have strong reason to 

 believe exist there in enormous numbers. 



As a basis for our studies Ave have ac- 

 cepted chemical analyses of many kinds of 

 protoplasm and selected what seemed to be 

 the minimum essentials. We said that 90 

 per cent water, 7 per cent protein, 1 per 

 cent fatty substances, and the remaining 2 

 per cent of other organic and inorganic sub- 

 stances are acceptable as constituting such 

 minima. Of these the water molecule was 

 the simplest conception and the best under- 

 stood. The protein materials, however, oc- 

 cupied most of our time. This substance 

 is the least well known and subject to the 

 widest variations in interpretation. There 

 are certain characteristics, however, which 

 come in for less objection, and these Ave 

 have made use of to furnish a tangible 

 structure, a frame of reference, in a sense, 

 for the structures in protoplasm. 



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