TRACE ELEMENTS IN ANIMALS 143 



iodine in its molecule. In various parts of the world where 

 iodine is deficient in the soil and where, in consequence of this, 

 very little of this element is absorbed by pasture plants, farm 

 animals may be liable to goitre, as, for example, in parts of Cali- 

 fornia and the Middle Western United States. Affected animals 

 are born with necks swollen as the result of enlargement of the 

 thyroid gland and are generally weak or dead. According to 

 Maynard (1937) iodine deficiency in dairy cows can be cured by 

 adding 0-02 per cent to the food given to the animals. 



Actually man appears to be more liable to goitre than farm 

 animals, and in this country, where animals are rarely affected, 

 there are areas, particularly in Derbyshire, where the incidence 

 of goitre among the human population is quite high and where 

 special measures in the way of administering iodine have to be 

 taken to combat it. 



It should be noted that although there is no doubt of the 

 beneficial effects of iodine in the treatment of goitre doubts 

 have been expressed as to whether iodine deficiency is the sole 

 factor responsible for this condition. It has, for example, been 

 quite widely held that the presence of radioactive material in 

 the soil is also a factor responsible in part for goitre. 



Manganese Deficiency in Chicks. Perosis. The very wide 

 distribution of manganese throughout the animal kingdom 

 suggests that this element may be as generally essential to 

 animals as to plants. It is thought that manganese in small 

 quantity is necessary for man although its function in the 

 human body is not known. As a result of experiments with rats 

 it has been suggested that manganese may be an essential 

 catalyst in the utilization of vitamin B l3 since .deficiency of 

 manganese in the diet brought about similar changes, for 

 example, loss of maternal instinct and progressive loss of 

 fertility, as excess of vitamin B x (Perla, 1939). 



The effect of manganese deficiency in bringing about a disease 

 of young chickens known as perosis, hock disease or slipped 

 tendon was first shown by Wilgus, Norris and Heuser in 1936. 

 This disease is characterized by a deformity of the leg bones, 

 and to some extent of the wing bones, of the chick, particularly 

 of the tibio-metatarsal joint. The bones of the leg and wing are 

 shorter than the normal. The relationship of manganese deficiency 



