432 PROTOPLASM 



Sulphur. — Sulphur is a constituent of, and therefore necessary 

 to, the synthesis of proteins in plants. It has occupied a promi- 

 nent place in the economy and thoughts of man for ages. We find 

 it referred to in the relation of fire and brimstone. Among the 

 alchemists, sulphur played an important role in their endeavors 

 to transmute base metals into silver and gold. In agriculture, 

 sulphur, as such or in simple compounds, has long been found of 

 value in aiding the growth of vegetation and in checking para- 

 sites. In medicine, it has been found of use in skin applications. 

 Within recent years, certain sulphur-containing organic com- 

 pounds, in particular cystine and its reduced form cysteine, have 

 become recognized as necessary ingredients in diet. A diet lack- 

 ing in cystine will not support life. (The hair, the skin, and the 

 nails are in large part made up of cystine in complex form.) 



Quite recently, it has been found that the cysteine complex 

 glutathione plays a prominent role in cellular metabolism. 

 Insulin, the pancreatic hormone regulating sugar metabolism, is 

 such a complex. Other sulphur-containing compounds have 

 come into prominence of late. The active principles of the 

 posterior pituitary gland (page 509) contain sulphur as a vital 

 part of their chemical constitution. It becomes more and more 

 evident that sulphur, free and combined, is exceedingly impor- 

 tant in health and disease. 



The significance of another sulphur combination, viz., the 

 sulphhydryl radical, SH2, will be considered elsewhere (page 520). 



The sulphur bacteria are an outstanding instance in which 

 nature has raised the element to a high position in the physiology 

 of the cell. These bacteria use sulphur instead of carbon in the 

 synthesis of higher foods. 



Sodium. — Sodium undoubtedly plays a more important role 

 than that usually ascribed to it, viz., as a physical agent in main- 

 taining equilibrium (osmotic, electric, etc.), but we are unaware 

 of its full role. Sodium chloride was early known to be 

 a constituent of all animal fluids and was experimentally used 

 as a medium in which to bathe organs and tissues for study in 

 the living condition. 



It has long been observed that in patients suffering with Addi- 

 son's disease, in which the adrenal glands are not supplying an 

 adequate amount of secretion for the body's needs, the amount of 

 sodium chloride in the blood is considerably below normal. The 



