212 SECTIONAL ADDRESSES. 
similar and the sheep show symptoms which resemble those described 
by Aston. 
The effects of deficiency of iodine already referred to are interesting 
in this connection. In Montana there was a very high mortality among 
young pigs, the annual loss being estimated at a million pigs. It was 
found that thecause of death was deficiency of iodine in the food of the sows. 
The vegetation of the district is poor in iodine, but the high mortality can 
be completely prevented by administering very small doses of potassium 
iodine to the sows. 
These examples of malnutrition in stock, associated with deficiency of 
one or more mineral elements in the food, are sufficient to show that the 
dietary conditions which produce such forms of malnutrition are fairly 
widespread. They also show that there is a possibility of remedying the 
defects if the nature of the deficiencies be known. 
The best method of securing a sufficient supply of all the essential 
mineral elements is,’ of course, to feed foodstuffs containing ample amounts. 
Unfortunately, with the exception of milk and good mixed pasture, such 
are not available. Modern intensive methods of feeding depend on the use 
of ‘ concentrates’ which are in almost all cases poor in one or more in- 
organic constituents. Animal products containing bone, such as fish-meal 
and meat-meal, are rich in some of the constituents deficient in concen- 
trates, and the incorporation of these products in the ration helps to adjust 
its mineral content. The well-known beneficial results of including these 
in the diet depend largely on this adjustment. Successful attempts have 
also been made to supply deficient minerals by the addition to the food of 
inorganic salts. Calcium phosphate, chiefly in the form of bone-meal, 
chalk, sodium chloride, iron and iodine have all been used, sometimes in 
combination as mineral mixtures, and in a great many cases a remarkable 
degree of success has attended their use. 
In order to be able to make such adjustments, it is necessary to know 
the amounts of each of the minerals which should be present in the ration 
to meet the requirements of the animal. But this depends on the extent 
to which they are absorbed from the alimentary canal. There might 
be an abundance in the food, but owing to factors which affect absorption 
adversely, only a small proportion of what is present in the food may pass 
through the wall of the intestine into the metabolic field. For example, in 
the case of calcium, which is probably the element which involves most 
difficulty in this respect, the amount absorbed, as calculated from the in- 
take in the food minus the output in the feces, may vary from nil to 
over 80 per cent. of the amount ingested. 
It is thus obvious that the factors which affect the absorption and ; 
utilisation of minerals are as important as the absolute amounts of minerals — 
present in the food. Unfortunately these factors are imperfectly under- 
stood. Reference may be made to two on which a great deal of work is 
being done at present, viz. the ‘ balance’ of the ration, and ultra-violet 
irradiation. 
Excess or deficiency of one mineral element may interfere not only 
with the absorption but also with the utilisation of another. Thus, for 
example, excess of magnesium interferes with the assimilation of calcium, — 
the ratio of sodium to potassium affects the assimilation of both calcium 
