374 ANIMAL BIOCHEMISTRY 



ances. In severe cases cerebral edema causes mental confusion, and 

 there is collapse of circulatory function and death. 



An excess of salt raises the osmotic concentration of the extracellular 

 fluid and withdraws water from the cells. If extensive, drastic changes 

 occur leading to severe metabolic disturbances, hallucinations, and 

 death. Animals normally do not eat enough salt to produce this condi- 

 tion except when drinking sea water in the absence of fresh water. 

 Then, of course, the salts of the sea water merely dehydrate the cells 

 more quickly and intensify thirst. 



Of the ingested Cl~, 90 per cent or more is excreted in the urine, 

 about 5 per cent in perspiration except during heavy exercise in hot 

 weather, and perhaps 1 per cent in feces. None of these figures can 

 be considered fixed indexes because all are markedly affected by the 

 rate of ingestion, physical activity, liquid consumption, and environ- 

 mental temperature. 



Cobalt 



Since vitamin Bj^ (page 345) probably occurs in the cells of all ani- 

 mals and is essential for their normal metabolism, cobalt must be 

 supplied at least in this form. Certain peptidases from mammalian 

 tissues require metal activators, and Co++ is the most effective ion. 

 Since other metals do work in vitro, it is difficult to know whether 

 cobalt plays this role inside living cells or not. This same situation 

 exists for a few other known enzymes, so it is possible that cobalt 

 plays other required roles than that in vitamin B^o. 



Daily allowances have not been set with any degree of confidence 

 because of the exceedingly small amounts needed. Cobalt deficiencies 

 in Australian sheep have been prevented with only 2 mg. of Co++ per 

 year. Moreover, forage from pasture lands supporting healthy cattle 

 and sheep can contain as little as 0.1 part of cobalt per million parts 

 of dry matter. If the grasses contain less than 0.07 p. p.m., ruminants 

 are likely to suffer. For some reason, pastures incapable of providing 

 adequate Co++ for cattle or sheep maintain horses in perfect health. 

 Either the ruminants themselves have higher requirements, or more 

 probably the rumen bacteria have sizable needs of their own for jiroper 

 growth. In marginal areas 10 g. of cobalt sulfate per 100 lb. of sodium 

 chloride fed free choice is probably adequate. Since meat is an excel- 

 lent source of B12, man and the carnivores never show deficiencies ex- 

 cept in human pernicious anemia, discussed on page 346. 



Cobalt deficiencies in cattle and sheep have been encountered in 

 Australia, New Zealand, Africa, Canada, parts of Latin America, 

 Britain, Central Europe, Michigan, New England, North Carolina, and 



