944 guanoxan and the

aliphatic oxidation of phenacetin. Genetdetermined polymorphisms of oxidation at carbon centres of drugs may be more prevalent than hitherto realised, and it does seem that there is at least one component common to the oxidative metabolism of such structurally dissimilar centres -as aromatic, alicyclic, and aliphatic carbon atoms which is under genetic control and exhibits polymorphism. ically

R. L. SMITH Department of Biochemical and Experimental Pharmacology, St Mary’s Hospital Medical School, London W2 1PG

J. R. IDLE A. A. MAHGOUB T. P. SLOAN R. LANCASTER

HYDROGEN PEROXIDE IN PREVENTION OF WATER CONTAMINATION

SIR,-In an editorial on inhalation fevers (Feb. 4, p. 249) you note that in all reports "symptoms could be related to inhalation of air contaminated by microorganisms, usually from humidifiers". Bacterial contamination of water is not unusual: within hospitals sources of potentially contaminated water include cold nebulisers, mist tests, humidification water in ’Isolettes’ and Armstrong units in nurseries, eyewash bottles, water baths (especially those used for thawing frozen plasma and heating infant formulae), ’Blanketrol’ ice mattresses, partially filled bottles of "sterile" solutions, and flower vases. A statement by J. G. Davis’ that "from many points of view hydrogen peroxide is an ideal sterilant for the food industry, as it readily decomposes into water and oxygen" led to an investigation of this compound to control bacterial contamination in water sources. 3% commercial H202 in small quantities will prevent bacterial multiplication. 10 ml of 3% H202 added to 1 litre of water killed 106 colony-forming units/ml of a variety of microorganisms including the ATC strains derived from the Roche ’Bac-Chek’ set (E. coli, E. cloacce, Ps. ceruginosa, P. vulgaris, S. typhimurium, S. aureus, and S. pyogenes). An approximate 80% kill was found in an hour, with no viable organisms after overnight incubation (18 h) at either room temperature (22°C) or 37°C. 30-60 ml of 3% HP2 controlled contamination of water in flower vases.2 Smaller quantities will often be sufficient to prevent bacterial multiplication in water sources. In isolettes 5 ml 3% H202 per litre of water has prevented contamination of the water reservoirs at this hospital for the past 6 years. With many other water sources, 10 ml of 3% HP2 will control contamination, provided the same ratio is maintained as make-up water is added. With blanketrol units, approximately 750 ml must be added per unit. With heavy contamination, periodic cleaning must also be used. Since H202 slowly decomposes it must be renewed periodically, especially if foreign material is introduced. The germicidal properties of H202 are probably the result of nascent oxygen. The official aqueous solution (3%) has a low toxicity rating,3 and Schumb et al.4 state that H202 "is not toxic in the usual sense" and that "man is admirably adapted to withstand treatment with hydrogen peroxide, the skin being relatively inert and the tissue fluids having an efficient means for decomposing hydrogen peroxide encountered internally". H202 has been recommended for disinfection of water supplies.s In view of its safety, cheapness, and efficacy in controlling contamination in water H202 warrants an investigation in large-scale humidification systems. Department of Microbiology, Richmond Memorial Hospital, Richmond, Virginia 23227, U.S.A.

A. L. ROSENZWEIG

Davis, J. G. Chemical Sterilization. Progress in Industrial Microbiology, London, 1968. 2. Rosenzweig, A. L. Lancet, 1973, ii, 568. 3. Gleason, M. N., and others. Clinical Toxicology of Commercial Products. Baltimore, 1969. 4. Schumb, W. C., and others. Hydrogen Peroxide. New York, 1955. 5. Yoshpe-Purer, Y., Eyland, E. Hlth Lab Sci. 1968, 5, 233. 1.

SPLEEN SIZE AND PREVIOUS TONSILLECTOMY IN AUTOIMMUNE DISEASE OF THE THYROID

SIR,-Graves’ and Hashimoto’s diseases are thought to have an autoimmune basis.’ Splenic atrophy has been observed in thyrotoxicosis/.3 though it is not clear at what stage in the disease splenic atrophy takes place. We have assessed spleen size in patients with thyroid disease, and looked for other evidence of autoimmune disease. Splenic size was estimated from technetium-99m sulphur colloid scans in 32 consecutive patients admitted for thyroid surgery. No patient showed splenic atrophy, but 7 out of 13 patients with thyrotoxicosis, 3 out of 10 with Hashimoto’s disease, and 1 out of 9 with colloid goitre showed some splenic enlargement. No correlation was found between spleen size, duration of disease, or presence of circulating thyroid antibodies. We next looked for evidence of previous immunological disturbance in 138 thyroidectomy patients. Most patients were uncertain of the details of childhood illness, but a history of tonsillectomy was recalled by 80% of 15 patients with Hashimoto’s disease and 66% of 48 with thyrotoxicosis, but only 10% of 75 patients whose thyroidectomy was for colloid goitre (P