If ATE R 



553 



Mineral or clicinical constituents m:iv cause epidemic i^oitre, 

 plumbism, lead colic, urinary calculi ( ?), cretinism, &c. 



Brackish water often causes diarrlicea in those newlv coming- into 

 the district. 



Excess of alkaline carbonates causes constipation. 



A large number of non-pathogenic bacteria will cause muco- 

 enteritis. 



Suspended clay, mica, quantities of sodium, calcium and mag- 

 nesium salts will cause intestinal disorders. 



Putrefying carcases of horses, cattle and humans will lead to 

 diarrhoea and dysentery. 



Dysentery is nearly always due to a contamination bv excremen- 

 titious matter, both bacillary and amoebic, but urine is another factor 

 in typhoid cases. 



The ova and embryos of entozoa and leeches pass to the body in 

 impure water. 



WATER— CONTROL. 



A suitable qualified Medical Ofificer must control the Avater supplies 

 on behalf of the Company or Sanitary Authority. 

 His supervision must include : — 



A knowledge of the " life-history " of the water. 

 The systematic inspection of the source, gathering ground, 

 reservoirs, means of conveyance and the control of the 

 storage tanks, filter beds, &c. 

 The physical, chemical and bacterial examination of samples 

 from various points of the supply. 



WATER— SOURCE OF CONTAMINATION. 



Elementary tests are very useful to ascertain the source of con- 

 tamination and often of its nature. This preliminarv being necessarv 

 previous to the adoption of purifying measures. 



Where apparatus and chemical reagents are not to hand obvious 

 contaminations should be dealt with at once without awaiting analysis. 



To ascertain source of contamination test by putting chemicals in 

 the water and searching for them later elsewhere, e.g., 



(i) Sodium chloride is traced by the silver nitrate test. 



(2) Lithium chloride is traced by the evaporation of quantities of 



the water, the residue gives a crimson colour. One part in 

 one million can be recognized. The test is expensive. 



(3) Ammonium chloride can be traced in one million gallons of 



water if seven pounds of the salt are used. 



