204 INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ III, II

Smith (88) that premature birth and imperfect development of the young in pigs
could be prevented by administration of iodine to the sows. Stiner (89) and
Schropp (90) have both found that administration of iodine, either as an inorganic
salt or in pasture manured with iodine, had a beneficial effect on fertility, the
number of services required being reduced. Muller-Lenhartz and v-Wendt (91)
found similar results to follow the feeding of a mineral mixture containing cal-
cium, phosphorus, iron and iodine.

It has also been suggested that conditions of relative iodine deficiency might
arise in areas where deficiency of iodine is not thought to occur, under conditions
of intensive feeding. The results of a four years' experiment at the Rowett In-
stitute suggest that in stall-fed cows there may be a relative deficiency of iodine
adversely affecting reproduction (communicated).

Fluorine excess.—Experiments are accumulating to show that an excess of
fluorine in the diet may have a detrimental effect on fertility. Since excess of
fluorine occurs under natural conditions in at least two known areas (Morocco and
some districts in U. S. A.), the experimental findings may be of some practical
significance. In Morocco, excess of fluorine in the drinking water gives rise to
pathological conditions in sheep (52, 53, 54) and in the U. S. A. a similar excess is
held responsible for abnormal dental enamel in man (55).

McCollum and his co-workers (56) found that feeding fluorine as sodium
fluoride at a level of 0.05 per cent. of the ration had no effect on fertility.
Similarly, Schulz and Lamb (57) found no impairment of reproduction from feed-
ing 0.05—0.1 per cent. of the ration as sodium fluoride, but Bergara (58), feeding
5 mg. sodium fluoride per rat per day, failed to get reproduction. Del Castillo
(59) and Chaneles (60), also found injurious effects. Velu (61), on the basis of
experiments in which he has shown that continued administration of fluorine
to rats causes suppression of the cestrous cycle, suggests that similar effects
may be produced in domestic animals from long-continued consumption of
fluorine-containing water.

Protein deficiency and excess.—In natural grazings a deficiency of phosphorus
is usually correlated with a low nitrogen content of the pasture, especially in the
mature herbage and under drought conditions. Hart (37) from his observations
on range pastures, lays stress on the dual deficiency. In many cases it would be
impossible at present to judge what part of the effect of such grazing in reducing
fertility is due to under-nutrition and what part to deficiency of phosphorus or
protein.

Numerous experiments on small animals have been made which show the
great importance of both the amount and the quality of the protein supplied for