150 TRACE ELEMENTS IN ANIMALS 



The possibility that cobalt deficiency may also be met with 

 in cattle in Kenya and in Florida has already been mentioned. 



It is now recognized that pining in sheep occurs in various 

 parts of England, notably in parts of Northumberland and 

 Cumberland and on Dartmoor and Exmoor in Devonshire. 



3. The Functions of Trace Elements 



in Animals 



The trace elements which have been shown to be essential for 

 animals of one or more species include iodine, manganese, 

 copper, zinc and cobalt. It has already been mentioned that 

 iodine enters into the composition of thyroxine, one of the 

 amino-acids of thyroglobulin, the protein of the thyroid gland. 

 This appears to be the only function of iodine in mammals, as 

 far as is known at present. Copper has long been known to form 

 part of the molecule of haemocyanine, a pigment concerned in 

 the respiration of certain Crustacea and some other lower 

 animals, while Mann and Keilin have shown that copper protein 

 compounds, haemocuprein and hepatocuprein, occur in the 

 blood and liver respectively of mammals. Although the actual 

 part played by these compounds in the physiology of the animal 

 is not clearly understood, it would appear to be established that 

 the functions of copper, wholly or in part, are to be found in 

 the roles of these copper-protein compounds. 



Although diseases are now definitely associated with defi- 

 ciencies of manganese and cobalt nothing precise is known of the 

 functions of these elements nor in what form they are present 

 in animals. With zinc, on the other hand, the reverse is the case, 

 for whereas no condition has been associated with deficiency of 

 this element, recent work by Keilin and Mann (1940) has thrown 

 considerable light on the function of zinc in animals. 



In 1933, Meldrum and Roughton showed that in the erythro- 

 cytes (red blood corpuscles) of mammals there occurs an en- 

 zyme which catalyses the reaction H 2 C0 3 = C0 2 -(-H 2 0. To this 

 enzyme they gave the name carbonic anhydrase. The enzyme 

 was shown by Davenport in 1939 to occur in relatively high 

 concentration in the gastric mucosa of mammals. It has now 

 been found by Keilin and Mann (1940) that preparations of this 



