EEVIEW — TEOPICAL MEDICINE, ETC. 227 



suspected area of contamination and to pump the neighbouring wells with a view to Water- 

 detecting the presence of fluorescein. These observers frequently found that, by ordinary coniinited 

 examination, fluorescein could not be detected unless the fluorescein-containing sample 

 was first concentrated by boiling and the remaining deposit filtered off. 



McCrae and Stock state that for the recognition of fluorescence caused by fluorescein, 

 it is preferable to examine the solution against a dark background rather than against a white 

 one, and that the use of magnesium light is unnecessary. Further, they found that the 

 addition of an alkali to the fluorescein was essential, as in acid solution fluorescein does not 

 give a characteristic green fluorescence. Copeman states that fluorescence is appreciable 

 in a dilution of 1 in 100,000,000, and if the concentration method for detecting the presence 

 of fluorescein be used, the delicacy of this recognition can be increased. 



MoCrae and Stock found that 2^ litres can be concentrated for this purpose, 

 evaporation of the water rendering the detection of fluorescein more delicate. They state 

 that concentration should not be carried too far, the best results being obtained when the 

 volume was not reduced below 5 c.c. It is usually necessary to filter the concentrate and to 

 wash the filter paper in 1 c.c. or 2 c.c. of water. 



If the water contain iron, care must be taken not to confuse in the concentrate the 

 greenish colour due to the presence of this metal with the green tinge of fluorescein. 

 The appearance of the fluorescein wiU be the longer delayed the finer the material through 

 which the water passes. 



Lake waters are as a rule very pure, this being chiefly due to the fact that the 

 suspended matters subside, while, owing to the great expanse of water, free oxidation occurs. 



The lower forms of plant life, such as algx, are liable to develop, but this difiiculty can 

 be got over by screening and filtration. The natural condition of the country surrounding 

 surface waters affects tlie purity of these waters. The ground around the collecting area 

 should if possible be free from cultivation and should not be inhabited. There is some 

 advantage in having trees planted over the collecting grounds, as they prevent water 

 rushing down in torrents to the lakes and reservoirs, holding it up and allowing of a 

 constant flow. 



The system of carrying water from open reservoirs to towns and villages by means 

 of open conduits is one to be condemned as dangerous, owing to the great risk of contamina- 

 tion by the insanitary habits and customs of natives. 



Rivers as a source of water supply are not liable to so much pollution in the Tropics as 

 one would imagine, owing to their greater volume, but during a period of heavy rain, they 

 frequently become contaminated by I'eceiving the contents of sewers and the excreta and 

 filth of towns and villages on their banks. Small and shallow rivers are very liable to be 

 polluted, owing to the fact that during the dry season the river beds are liable to become 

 dry and filled up with all kinds of filth and pollution, so that at the commencement of the 

 rains the water in them contains a large amount of filth. It often happens that the river 

 is used for purposes of ablution at the same spot that water is obtained for drinking 

 purposes. This can be avoided by setting aside the part of the river highest up stream for 

 drinking purposes, and that for ablution lowest down. 



Ponds and tanks are frequently used, especially in India, as a source of water supply. 

 They are liable to contamination owing to the filthy habits of the natives, periodically become 

 infected with cholera germs, and form a suitable nidus for all kinds of parasites. 



In tanks and wells infected with the cholera germ, disinfection by means of potassium 

 permanganate gives excellent results. For an ordinary well four ounces of potassium 

 permanganate is about the net amount required, but more may be necessary. Eoughly 

 speaking, the correct amount is that which will colour the well-water pink for half-an-hour. 

 It is an advantage to dissolve potassium permanganate first, before adding it to the well, 

 and a further advantage to add it to the well in the evening. 



Lime has also been used for disinfecting purposes, the strength being one ounce to a 

 cubic foot of water. 



A new method for the disinfection of drinking-water is described by Paterno and 

 Cingolani.' These authors have applied silver fluoride (Tachyol) for the purpose of 

 sterilising water. In a strength of 1 in 400,000 it was found to destroy all organisms 

 except the B. subtilis and a few others of no importance, its action being more effectual than 



' Paterno, E., and Cingolani, M. (October, 1907), "A New Method for the Disinfection of Drinking- Water." 

 Journal of Ihe Royal Institute of Public Health. 



