226 REVIEW — TROPICAL MEDICINE, ETC. 



Water— health of Indian stations by paying more attention to the geological formation of the 

 continued ground in the vicinity of the station, and especially to the origin, course and protection of 

 the sub-soil water. He further suggests that a contour map of the sub-soil water should be 

 made by an engineer, and that information regarding the rise and fall of sub-soil water and 

 other necessary geological data should be collected at every station and the necessary maps 

 prepared, so that if any building or entrenching is to be done, the direction of the flow 

 of the sub-soil water will be known. Entrenching of grounds should always be carried 

 out on the downstream side of the sub-soil water supply to a station. Shallow wells are 

 more commonly used than any other variety, and as they draw their supply of water from 

 the sub-soil water, certain conditions are absolutely essential before the sub-soil water can 

 be trusted. (1) the locality should not be thickly populated ; (2) the refuse disposed of 

 must be spread over wide areas and not placed in deep pits ; (3) there must be a living 

 surface, and on no account must this be removed ; (4) the porous filtering soil should be 

 of sufficient thickness. It is important also to know the character of the filtering media. 

 If of a sandy nature, purification is greatly assisted by oxidation ; but if, on the other hand, 

 the sub-soil consists of clay, purification is practically impossible, as the clay virtually acts 

 as a culture medium, especially in the case of a sub-soil consisting of black clay. The 

 formation of fissures and the presence of disused wells, which are frequently used by 

 natives for insanitary purposes, are other factors which constitute sources of pollution 

 for a water supply. 



The ever-present difficulty of surface well contamination in the Tropics can be 

 surmounted by the use of tube or Abyssinian wells. The tube well consists chiefly of an iron 

 tube of a diameter varying from 1\ to 4 inches, which has at its lower end a steel point for 

 boring purposes. Above the point the tube is perforated for some distance to admit water. 

 By means of a weight attached to a tripod the tube well is driven into the ground till water 

 is reached. The upper end of the tube is so constructed as to allow of another tube being 

 coupled on to it. Whenever water is reached a pump is attached. The tube well may 

 tap the ground water overlying the first impermeable stratum, or it may sink lower than 

 this so as to reach a second water-bearing stratum. The bore well has the advantage 

 over the tube well in rapidity in sinking. Deep wells and springs usually provide a pure 

 water, as the filtration through the soil has been so complete as to render the water free 

 from organic matter. 



Wells should always be efficiently protected, and should be lined and cemented. The 

 area of the ground around the mouth of a well should be concreted with a slope away 

 from the well, and a raised parapet can with advantage be built so as to prevent surface- 

 drainage flowing in at the top. The suction pipe should be placed at the side of the 

 well, not immediately over it. 



Kochi devised a method of converting a shallow well into a tube well, and thus 

 protecting it from contamination by means of an iron pipe reaching from the bottom to 

 the top of the well, and by filling up the well to the highest water point with pebbles 

 and gravel and the remainder to the surface with sand. 



Various methods have been employed for the detection of suspected sources of 

 contamination, and certain chemical substances are used at the suspected source of 

 pollution and afterwards looked for in the contaminated waters. As a control, it is 

 necessary to examine the water first to ascertain that there is not naturally in it any of 

 the substance to be employed in the test. 



The chief soluble chemical substances employed are fluorescein, lithium chloride and 

 common salt. The presence of lithium chloride in the contaminated water is detected by 

 spectroscopic examination, that of common salt by means of the silver nitrate test, while 

 fluorescein gives a green fluorescence in the presence of an alkali. Dr. Beam, of the 

 Chemical Laboratory, Gordon College, has introduced a new method of detecting the 

 slightest trace of fluorescein, an account of which is given in his report. As regards the 

 use of fluorescein as an agent for the detection of pollution of wells, if a connection can be 

 established by means of fluorescein between a spot known to be contaminated and the 

 source of water supply, such supply should be considered as dangerous and liable at any 

 time to give rise to a water-borne epidemic. 



McCrae and Stock- conducted a series of experiments in connection with the use of 

 fluorescein in South Africa. The method employed by them was to place fluorescein in the 



• Koch, R. (July 22nd, 1905), " Annotation." Lancet. 



" McCrae, J., and Stock, P. Q. (April, 1907), " Experiments with Fluorescein." Journal of Hygiene, p. 182. 



