376 ANIMAL BIOCHEMISTRY 



these requirements. In areas with deficient vegetation, salt licks con- 

 taining 0.25 to 0.5 per cent copper sulfate prevent deficiency symp- 

 toms. 



Since copper plays a diversity of roles in animals, lack of it leads to a 

 variety of symptoms depending to some extent on the species and stage 

 of maturity. Anemia is a general response, and depigmentation of the 

 coat, retarded growth, bone disorders, diarrhea, abnormal hair growth 

 and structure, and nerve malfunction are more or less common symp- 

 toms. Black sheep, for example, turn to gray, and all sheep regardless 

 of color develop limp and shiny wool fibers. The animals find it 

 difficult to walk, staggering and falling because muscle control is im- 

 paired by lesions of the nerves. Death can occur quite suddenly. 

 When alternations of bones and nerves are not severe, administration 

 of Cu + + is rapidly effective. 



An excess of copper is dangerous, for Cu++ is fairly toxic. Hence 

 the indiscriminate feeding of this element is risky. Sheep given 30 mg. 

 of copper salts daily over an extended period develop hemolytic jaun- 

 dice as a symptom of copper poisoning. 



Excreted copper appears primarily in the feces, including the ingested 

 but unabsorbed fraction. That eliminated from body tissues seems to 

 be mainly lost to the intestinal tract by way of the bile. Urine is low 

 in copper except in kidney disorders. 



Fluoride 



Although this anion has probably received more attention than 

 any other trace element, its status is still much in doubt in most 

 respects. In fact, there is still no conclusive demonstration that fluo- 

 rine is essential to either animals or plants. One interesting recent 

 experiment indicates that rats fed plants and yeast grown in "fluorine- 

 free" systems grow more slowly than rats on the same diet supple- 

 mented with fluoride. Since the diets were not analyzed for fluorine to 

 permit comparison with other studies, the experiment should be re- 

 peated with all analyses and controls. Other work using diets very 

 low in fluoride gave erratic results or no signs at all of deficiency. 



Whereas fluorine may or may not be a strictly essential element, 

 there is no doubt about its occurrence in teeth, bones, and other body 

 tissues. In the case of teeth, at least, F- is beneficial when ingested at 

 certain levels and markedly reduces the incidence of dental caries, 

 especially in children. Apparently fluoride is most effective during the 

 formative stages of teeth, but the protection conferred carries over to 

 adulthood. In the laboratory, dental caries experimentally produced 



