180 



THE CELL AND PROTOPLASM 



tance for hydrated particles with a layer of 

 water molecules bridging the back-bone of 

 one chain directly to that of its neighbor. 

 In the other direction, perhaps at nearly 

 right angles, the side-chain spacing may 

 vary and be far less uniform. The distance 

 between chains may average up to 18 A to 

 20 A, if we may accept studies with gelatin 

 as a basis. The degree of hydration, or the 



single layers, resembling the monolayers 

 which have been shown experimentally to 

 exist (Langmuir 1938; Langmuir and 

 Schaefer 1939; Astbury, Bell, Gorter and 

 van Ormondt 1938). Or in contrast, these 

 packets of 50 A size could conceivably be 

 built up into much larger three-dimensional 

 particles. There is some experimental evi- 

 dence for both of these assumptions, but we 



HYDRATION OF GELATIN 



10.4 A 



O O 



o 



o 



•< 

 o 



o o 



I3.0A 



Fig. 7. Hydration of a protein chain shown in diagram. The end views of four chains are shown at A 

 where no water is present. At B, 15 per cent water produces a lateral spreading; the water is repre- 

 sented by the large circles. At C, 33 per cent water produces greater lateral spreading and in addition 



vertical separation also. 



amount of bound water, will affect consid- 

 erably the size of the particles. With 40 to 

 50 per cent water and a density equivalent 

 to about 1.15, the density of cytoplasmic 

 jDarticles, a protein particle of 36,000 mo- 

 lecular weight could take a globular oi- 

 cubical form of about 50 x 50 x 45 A ; while 

 if more highly hydrated it might be 50 per 

 cent greater along one or two axial direc- 

 tions. 



Conceivably this ]icirticle could become 

 completely subdivided into fiat discs of 



need much more before we should accept 

 them without reservation. It is conceivable 

 also that the flat discs of a single layer of 

 chains could become aggregated laterally 

 and form a so-called monolayer of about 10 

 A to 15 A in thickness, and of more or less 

 indefinite lateral extent. Although there is 

 a certain amount of experimental evidence 

 for this monolayer formation, no evidence 

 of its existence in cytoplasm has been pre- 

 sented up to this lime. 



These small pjii-lichN with llieir layered 



