PARATHYROID GLANDS 75 



except in young children. Wells finds that the 

 amount varies with the locality, and in general is 

 inversely in proportion to the local prevalence of 

 goitre. In parenchymatous goitre the iodine content 

 is too low ; in exophthalmic goitre it is too high. A 

 principal function of the thyroid is to control the 

 iodine metabohsm of the body. 



PARENCHYMATOUS GOITRE. 

 Directing our attention now to enlargements of 

 the thyroid gland, we rule out those that are merely 

 due to tumour formation, such as adenoma or cystic 

 disease, and confine ourselves to the parenchyma- 

 tous goitres. It has long been known that there is 

 some connection between drinking-waters and the 

 incidence of goitre. The disease is extraordinarily 

 prevalent in certain districts, and especially where 

 the water-supply is derived from particular geological 

 formations, such as the molasse in Switzerland 

 and the carboniferous Umestone in Derbyshire. In 

 Khokand, Turkestan, a very large proportion of the 

 whole population suffers, and Russian soldiers 

 stationed there rapidly acquire the disease. The 

 introduction of a new water-supply has several times 

 induced an epidemic of goitre in a town, or, on the 

 other hand, reduced the number of cases in an 

 endemic area. Thus at Rupperswyl, near Aarau, 

 an endemic area in which 59 per cent of the 

 children were goitrous, in 1884 the water-supply was 

 changed for one from a non-goitrous district, and 

 in ten years the percentage had fallen to eleven. 

 There are on the Continent certain goitre wells called 



