the electrodes connected to a high voltage alternating current circuit. Ozone generators are designed generally with a solid dielectric interposed between the electrodes. All ozonization plants for the purification of water consist of two parts, the generators where the oxygen. in the air is converted into ozone, and the scrubbers employed to bring the gas into intimate contact with the water. Nearly all of the many generators for the production of ozone have followed practically the same general design and operate in a similar way. They consist of an inside and outside electrode with a dielectric interposed between them. The elements are so placed as to permit air to be drawn or forced through the space between the electrodes. Usually the generators are cooled, and the air passing to the apparatus is dehydrated either chemically or by refrigeration. The amount of oxygen converted into ozone per unit of electrical energy expended varies with different machines.

The method employed to bring ozonized air into contact with the water is much the same in all systems. The ozone mixed with air is discharged into a scrubber chamber and thoroughly mixed with the water by passing through a bed of gravel, or by means of baffle plates. In the plant at Petrograd, Russia, gas scrubbing is used.

In 1919 there were between 60 and 70 municipalities in Europe employing ozone for the sterilization of public water supplies. The majority of these plants now in use are comparatively small, although some large units have been constructed and operated. The St. Maur system at Paris, with a daily capacity of 24,000,000 gallons, and the Petrograd plant in Russia, treating about 13,000,000 gallons of water daily, are notable installations.

Ozonization systems for the treatment of public water supplies in America have not proven successful, although many attempts have been made to use them. The efficiency of ozonization depends largely upon a thorough mixing of gas and water and an adequate contact period. The failure of many plants to function satisfactorily has been due to inefficient mixing. Water that contains suspended solids or is highly colored should receive preliminary treatment to remove these constitutents. Since ozone is an active ozidizing agent it may reduce the color in water, if it is of an organic nature. It is much cheaper, however, to remove such substances by filtration or treatment with chemicals, than by ozonization.

Ozone is a fairly efficient bactericide, but, for continuous effective

ness, the gas must come into direct contact with the organisms and must be in sufficient concentration. When these conditions are fulfilled complete sterilization is possible. Concentrations as low as one gram of ozone per cubic meter of air will sterilize some waters. The cost of ozone treatment is greatly in excess of chlorination.

CHAPTER XII

TREATMENT OF WATER WITH IODIDE FOR THE PREVENTION OF SIMPLE

GOITER

Introductory

A public health measure of absorbing interest and outstanding importance has gradually been introduced in this country during the last ten years. In the prevention of simple goiter by the administration of minute quantities of any form of iodin we possess an effective prophylactic against thyroid enlargement, especially during those periods of life when it is most prone to occur.

Simple goiter may be described briefly as an enlargement or swelling of the thyroid gland-a gland of internal secretion-which lies in the front part and somewhat to the sides of the neck. It may involve either one or both lobes of the gland and vary in size from the normal, which can scarcely be noticed, to the pendulous forms.

Two other types of goiter usually more serious in nature should be mentioned; one a definite nodular tumor which may undergo malignant changes and the so-called exophthalmic or toxic goiter associated with profound nervous symptoms and disturbed metabolism. With these forms iodin prophylaxis is not concerned. The treatment and cure of different kinds of goiter is strictly a medical and surgical matter. Many forms of treatment and prevention' have been tried all the way from incantations and amulets to radical surgical operation. No form of prevention, however, has given so much promise and proved so uniformly successful as the early administration of small quantities of some form of iodin. The prevention of simple or endemic goiter, therefore, may be considered a public health problem of prime importance.

Historical

The enlargement of the thyroid, now generally known as goiter, has been recognized as an abnormal condition for many centuries. There is some evidence that as far back as 2000 B.C. the Chinese were familiar with it and discovered that the eating of sea-weed and

the thyroid glands of animals, and the use of crude sea salt, would ameliorate or cure the condition. At any rate very little goiter has been noted along the China littoral. It is stated that one of the Hindu Vedas coming down from about 2000 B.C. contains a collection of incantations with certain religious rites against goiter. The early Greeks realized the seriousness of goiter and one of the methods advocated for its treatment was the giving of ashes from burnt sea-sponges, which we know must have contained considerable iodin. The Romans were quite familiar with goiter. Caesar in one of his descriptions notes the frequency of enlarged necks among the Gauls.

In Switzerland where goiter is endemic and has always been very prevalent Paracelsus, one of the most famous Swiss physicians who lived from 1493 to 1541, noted the relationship between endemic goiter and cretinism, a congenital condition associated with absence or deficiency of the thyroid gland resulting in dwarflike, dull, mentally inferior individuals. Captain Cook reported sporadic cases of goiter occuring among his sailors. In 1688 enlarged necks were described among the Indians of Peru and in 1787 we have descriptions of goiter in Mexico and soon afterwards from Central America. The early settlers in America noted the condition among the Indians in the western part of New York State and it was later described as occurring among the Indians in the Lake Superior region..

Geographical distribution

Enlargement of the thyroid has been observed not only throughout a long period of history, but it appears widely distributed geographically. It occurs so persistently in certain more or less circumscribed areas of the world that it has come to be known as endemic goiter. The most notable of these regions are in the Alps, particularly along the borders of south-eastern France, southern Germany, throughout Switzerland, southern Austria and northern Italy. In Asia the region of the Himalayas are especially affected, northern India and certain parts of western China and Mongolia. In South America the endemic goiter areas are along the Andes, on the high Peruvian plateau and in certain sections of western Brazil. North America also has its well marked regions where simple, or endemic, goiter is quite prevalent. The zone expands roughly from the basin of the St. Lawrence westward across the Great Lakes region and north

western United States to the Pacific Northwest taking in neighboring Canada, especially British Columbia and Alberta. The states of Washington, Montana, Michigan, Wisconsin and Minnesota are quite heavily affected. Nests of goiter appear in western New York State, in the foothills of the Appalachian mountains in northwest Pennsylvania and in western Maryland. In general, it is found most prevalent in mountainous regions or on high plateaus and in places some distance from the sea, although nests may appear at other places, for example in certain parts of Derbyshire, England where it has come to be known as "Derbyshire neck."

One of the most interesting observations regarding this disorder is that where it is prevalent among human beings it is liable also to affect widely the domestic animals. Thus it has been found in endemic goiter regions among the dogs, sheep, cattle, pigs, rabbits, and other species. Endemic goiter, therefore, is an economic as well as a sociologic and public health problem.

Iodin relation to the thyroid gland

Iodin was first isolated from sea-weed in 1811 by a Frenchman named Courtois, but it was not until 1895 that Baumann detected its presence in the thyroid gland. Iodin was used empirically in the treatment of goiter as early as 1820 by Dumas and Coindet. In 1850 Chatin began to publish the results of his epoch making investigations into the distribution of iodin in nature and its geographical relation to the presence of endemic goiter. On the basis of his preliminary studies he ventured the opinion that endemic goiter and cretinism were due to a lack of iodin in food and water and could be prevented by the continued administration of minute doses of iodin. Chatin proceeded to test his theory by systematic analyses of food products and waters from various districts for their iodin content. He was able to demonstrate that iodin was present in small quantities in a variety of natural foods, in waters from certain sources and even in the air near the sea-shore.

Chatin made a careful study of the iodin content of fresh water plants. On account of the scarcity of iodin in certain river waters which he examined he held that this must bear a causal relationship to the prevalence of goiter in the regions supplied by those rivers. He analysed the public water supplies of Turin and London to determine the amount of iodin and made studies of the Rhone water