water, there should be no ill effects on bathers' eyes, ears, etc. Are the costs of silver sterilisation the same as for chlorine?

Have the experiments with silver sterilisation been checked as to their effects? It had been found that minute quantities of some substances may be quite harmful to health.

Dr. Rothmann: There are no swimming pools in New Zealand equipped with silver sterilisation.

Operating costs for swimming pools depend largely on the operating cycle. They are roughly the same as for chlorine or a few per cent. higher.

As to effects on eyes, etc.: Chlorine must be very carefully regulated if these are to be avoided. However, even so some people are very sensitive to chlorine, and get inflammations, etc.

Even if the residual chlorine concentration is low and similar to silver it must be remembered that weight for weight one obtains a higher concentration for chlorine, which is a gas, as compared with silver, which is a metal.

Concerning the effects on health: My information goes only up to 1939. Until then all the facts reported in this paper had been checked frequently and in various countries and had all been confirmed.

Experiments on rats with very strongly activated water given for long periods showed conclusively after dissection, that no alteration in their tissues took place, nor did the general appearance of the rats indicate any different development from that of the control animals.

Mr. McLennan: Has silver been used for the sterilisation of city water supplies?

Dr. Rothmann: No, only for small communities. The cost of silver sterilisation for drinking water is higher than that for chlorine. On present-day prices it costs about 0.4d per 10,000 gallons of water with chlorine, but approximately 4d per 10,000 gallons with silver. This, however, is of minor importance, as the cost of sterilisation is only a relatively small fraction of the total cost of a water purification plant which includes pumps, filters, etc. (A diagram of comparative costs for three different projects for the city of Rome was shown on the screen.)

Mr. Korrick: Has silver been used for sterilising other liquids, such as, e.g., milk?

Dr. Rothmann: It is not suitable for milk as colloids would precipitate the silver ions. It can be used for washing cans and pipes, as in breweries.