MINERAL METABOLISM OF FARM ANIMALS                       285

tion. It was noted that there was an absence of udder development at parturition
and an obvious lack of milk during the suckling period. In a somewhat similar
experiment with cattle at Wisconsin, Hart and others⁵⁷ found that on a ration of
ground oats and oat straw, cows failed to breed or gave birth to dead calves. These
workers calculated that for normal reproduction, there should be 0.45 part of
calcium per 100 of the ration.

Much attention has not however been paid to other minerals. McGowan and
Crichton⁵⁸ studied the subject of iron deficiency in the case of young pigs. They
found that with a deficiency of iron, the young pigs gained in weight at fully the
normal rate, but were fat and flabby. The skin was paler than normal and in some
cases the hæmoglobin was as low as 25 per cent. of the normal. The death rate was
high. As a result of experiments on animals Hoslin⁵⁹ has also suggested that
deficiency of iron may be the cause of primary anæmia in children. Waddel and
others⁶⁰ recently showed the physiological function of traces of copper in hæmoglobin
building and Elvehyem, Hart and co-worker⁶¹ have shown the necessity of copper as
a supplement to iron in hæmoglobin formation in the pig. Orr⁶² states that a diet
containing too little salt produces in cows a staring coat, lustreless eyes and a
condition of general malnutrition with a decrease in milk yield. The condition
appears to be due to a lack of chlorine, and can be rapidly cured by giving either
sodium chloride or potassium chloride. An excess of chlorine however might lead
to pathological symptoms. Thus McCollum⁶³ regards an inflammatory condition of
the eyes, resembling xerophthalmia which he calls "salt ophthalmia" as due to
excess of chlorine in the food.

So far we have been considering malnutrition in cattle more or less under
experimental conditions. The importance of this mineral deficiency lies however in
the fact that some deficiency diseases, due to lack of minerals, are common in all
parts of the world. Thus Marine⁶⁴ studied the curative effect of iodine on goitre by
observations on sheep in Michigan. Severe losses occurred there through goitre
with which were associated certain pathological conditions and heavy death rate in
lambs. Ennis Smith⁶⁵ in Montana found a striking case of the effect of iodine in
preventing the birth of hairless pigs. Helmer⁶⁶ in British Columbia and Torrance⁶⁷
in Canada recommended administration of potassium iodide to sows, ewes and cows
as a prophylactic measure against goitrous conditions. Numerous other experiments
on the beneficial effect of iodine on a iodine-low ration have demonstrated its value
in the dieting of farm animals.

The most important of recent contributions to the study of mineral requirement
has been made on phosphorus deficiency by a group of workers in South Africa, and
a very recent paper by Theiler and Green⁶⁸ summarises the position of aphosphorosis