68 LIFE: ITS NATURE AND ORIGIN 



Hydro genation: According to Sabatier, traces of bromine adsorbed 



from the air of the laboratory, prevent the hydrogenation of 



phenol; and thiophene in benzene prevents its hydrogenation 



to cyclohexane. 



Dry Batteries: Iron in the pyrolusite ((Mn0 2 ) and copper in the sal 



ammoniac, both hurt "battery life." 



Since we are here most interested in the biological effects of 



"trace" substances, a few instances of the importance of mineral 



elements must be mentioned. Iodine is an essential constituent 



of thyroxine (4 atoms per molecule), an oxidation-accelerating 



hormone of the thyroid gland. Copper facilitates the formation 



of hemoglobin, and is a constituent of many oxidase enzymes 



(e.g., ascorbic acid oxidase, polyphenol oxidase, tyrosinase, laccase). 



Zinc is essential in carbonic anhydrase, which influences the 



equilibrium between the H3CO3 and C0 2 being carried by the 



blood. Cobalt is a vital element for sheep and cattle (seemingly 



not for rats). When some New Zealand sheep suffering from 



"bush sickness" were cured by administration of iron, it was at 



first thought that the illness was due to iron deficiency; but later 



investigation proved that a tiny amount of cobalt present in the 



iron as an impurity was responsible for the cure. 



Fluorine in minute amounts seems essential for proper tooth 

 structure, though in humans a slight excess causes trouble, such 

 as black and misshapen teeth. Vanadium is an important con- 

 stituent of the blood pigment of the ascidian Phallusia mammilata, 

 and F. Bernheim 7 found that vanadium stimulates oxidation of 

 phospholipids in the liver. Molybdenum is being recognized as 

 of biological significance; and some molds will not grow in the 

 absence of traces of gallium. Female rats fed on a manganese- 

 deficient diet gave birth to young but lacked maternal instinct; 

 and 97 per cent were unable to suckle their young, which were 

 also neglected by foster mothers, indicating that the latter detected 

 some deficiency. In fowls, manganese is essential to normal devel- 

 opment and is the inorganic factor preventing perosis ("slipped 

 tendon"). Professor E. V. McCollum of Johns Hopkins Univer- 

 sity and his collaborators have done noteworthy work on trace 

 elements in nutrition. 8 



Vitamins and Hormones 



These are considered together because they both represent sub- 

 stances essential in minute amounts for the normal development 



