392 ANIMAL BIOCHEMISTRY 



toxic quantities. At any rate himian cases of selenium poisoning have 

 not been definitely identified. 



Chronic poisoning in livestock is manifested by apathy and lack 

 of vitality, emaciation, roughness of coat, anemia, lameness due to 

 erosion of joints of the long bones, sore feet and partial loss of hooves, 

 loss of long hair from cattle and horses and body hair from pigs, 

 atrophy of the heart, and atrophy and cirrhosis of the liver. Acute 

 selenium poisoning is characterized by blindness, partial paralysis, 

 abdominal pain, excessive salivation, grinding the teeth, and death, 

 usually by respiratory failure. 



Adult fowl are not so drastically affected, but there is a reduction 

 in food consumption, growth, and egg production. Hatchability is 

 reduced, perhaps by levels too low to produce other symptoms in ani- 

 mals. The eggs are fertile but the embryos either fail to live to hatch- 

 ing or are grossly deformed monstrosities. 



The mechanism of toxicity has not been identified. Rather obvious 

 possibilities include interference with the metabolism of sulfur com- 

 pounds and the replacement of the sulfur of enzymes. In the latter 

 case the catalytic activity of those enzymes depending on — SH groups 

 would be modified or destroyed. 



Prevention and treatment are most unsatisfactory. Removal from 

 or fixing of the selenium in the soil has not been accomplished. Feed- 

 ing high-protein diets to some extent raises the level ingested without 

 toxicity and ought to be of practical value where the diet contains 

 borderline quantities of seleniimi. Administration of subtoxic levels 

 of arsenic as arsenite or arsenate prevents selenium poisoning at the 

 lower range of intake. In view of the potential hazard from this 

 treatment, it is not very useful in the field. Thus no procedure can 

 be recommended other than avoidance of the affected areas. 



Sodium 



This ion is closely associated with Cl~ in its ingestion, excretion, 

 requirements, and most of its functions. Therefore much of the mate- 

 rial discussed under chloride (page ?il?)) is directly applicable here. 

 In addition to its roles in salt and water balance, depending on 

 osmotic concentration and control of protein solubility, sodium ex- 

 changes with potassium ions during nerve and muscle operation. Al- 

 though the mechanism is in doubt, these functions are essential to 

 animals. Furthermore, about a quarter of the Na+ in the body oc- 

 curs in the skeleton in an insoluble, rather inert form presumably 

 necessary for the well-being of the animal. 



