I CYTOPLASM 163 



hydrates it also acts as a protector of atom groups which should not 

 be affected (hexose diphosphoric acid, phosphorus glyceric acid, etc.). 

 It is possible that in the cytoplasm the phosphatides, which can 

 combine with various groups of the polypeptide chains, render a 

 similar service. The elements O and S of the sixth row are primarily 

 bridge-building elewenis, since they interconnect the C-N-polypeptide 

 chains. Apart from this, oxygen can act as a chain-building element 

 in the high polymeric carbohydrates, and conversely N and C are 

 capable of bridge formation. 



The elements of the first and second row: Na, K, Cu, Mg, Ca, Zn, 

 and also CI occur in cytoplasm as ions and act as hydration regulators. 

 They do not form stable bonds but only heteropolar salt bonds with 

 the molecular framework (metallic organic compounds like chloro- 

 phyll, haemoglobin, etc. are quantitatively of minor importance). In 

 this respect the most favourable ions in plants are K, Ca and CI of the 

 so-called argon type (in animals Na takes the place of K). Both in 

 mixtures and in pure solutions these ions are tolerated in concen- 

 trations at which other ions are detrimental to the cytoplasm structure. 

 This would also explain why the nutrition line takes its course towards 

 argon. The higher valent elements B, Mn and Fe presumably enter 

 into some relation with the protoplasmic frame. As regards manganese 

 and iron, it is usually believed that their capacity to change valency 

 is put to use in metabolism. 



The most important part is played by the element hydrogen, both 

 as an ion and as an element. It regulates p^ and ry, thus preventing 

 the molecular framework from soUdifying, and maintaining the labile 

 changeable state which is so characteristic of protoplasm. 



c. Physical Properties of the Cytoplasm 



Sol properties. Many cytologists suppose the cytoplasm to be a Hquid 

 (Rhumbler, 1898). Heilbrunn (1930), for example, writes about the 

 amoeba: "it is a tiny sac of fluid in motion" and Chambers (1925) 

 considers not only the cytoplasm but also the nucleus to be a liquid 

 phase. 



The flow of protoplasm, the relatively low viscosity, the large water 

 content, the soft consistency, the convex shape in plasmolysis and 

 other indications point to the sol character of the cytoplasm, i.e., to 

 a state in which all submicroscopic particles have free relative move- 



