SANITARY CHEMISTRY

an important sub-division of Sanitary Science (g.v.). The chemical laboratory offers valuable aid to the sanitary engineer and public health officer, enabling him, by means of chemical analyses, bacteriological examinations and investigations of various kinds, to control the purity of foods and water, and in some cases to discover the cause of epidemics. Periodic examinations of the water supplies of all large cities and of most of the smaller towns are now made by the various health departments concerned. These examinations involve firstly a chemical analysis for the purpose of discovering sewage contamination, if present, secondly, a bacteriological examination to ensure the absence of pathogenic organisms, and finally a biological examination partly as a check on contamination and partly to detect the presence of organisms likely to produce undesirable flavor or odor in the water. <A striking example of the last named trouble occurred in 1922 in connection with the New York City water supply. For several days the water had a marked odor and flavor of cucumbers. It was caused by an organism known as the synura, readily detected by aid of the microscope. The sanitary chemist also undertakes the analysis of milk and other foods. He examines milk for dilution with water, or for abstraction of cream, butter for adulteration with foreign fats, or for the presence of undesirable preservatives, sausages and other meat-stuffs for preservatives, and every kind of food for adulterations with inferior or harmful products. He also keeps a check upon sewage disposal, and in_ those cities where chemical or bacteriological purifying systems are used, he makes periodical examinations of the sewage effluent to ensure that the proce is working efficiently. Finally, in many instances he is called upon to make bacteriological examinations of sputums, throat swabs and so on, in order to enable the health officer to check the spread of tuberculosis, diphtheria and other infectious diseases.