1 26 



HEALTH AND DISEASE 



es ®Q r . 



hardships of a water famine have constantly to be endured in consequence 

 of the absence of any means of storing. Presumably the question is one of 

 cost, and it unfortunately happens that those districts which suffer most 

 from scarcity of water in dry seasons are least capable of supplying funds 

 for the formation of the required reservoirs. 



A due recognition of the importance of a liberal supply of water for 

 hygienic purposes in thinly populated districts as well as in populous would 



be naturally followed by the adoption of a proper 

 system of inspection for the purpose of ascertaining 

 the quality of the water, including its degree of 

 hardness, whether arising from excess of carbonate 

 of lime or from other lime salts which cannot be 

 got rid of, and the employment of the proper 

 means for the purpose of correcting any objection- 

 able characteristics prior to the distribution of the 

 fluid. 



Means for these purposes are easily applied under 

 the circumstances referred to, but they are abso- 

 lutely impracticable so long as the supply of water 

 is drawn from ponds or from wells which in main- 

 places are open to pollution which can neither lie 

 prevented nor corrected. 



Natural Processes of Purification of 



Water. — Water in its most polluted form under- 

 goes certain chemical and physical changes which 

 have a distinct tendency to restore it to a wholesome 

 condition. Under all circumstances water contains 

 air, the oxygen of which acts with energy on septic 

 bodies, causing them to undergo a new form of 

 decomposition, resolving them into compounds of 

 carbonic acid and ammonia. Further and even 

 more destructive processes, the nature of which is not clearly understood, 

 also take place under the influence of oxygen. It has been observed, for 

 example, that water highly contaminated with sewage, so as to be quite 

 turbid, if left entirely at rest for a long period becomes absolutely odour- 

 less and perfectly transparent; and what is more remarkable, this change 

 is not the result of the subsidence of solid particles, but of the oxidation 

 and conversion of solid material into soluble compounds. It does not, 

 of course, follow that water under such circumstances will be fit for 

 drinking purposes, but the instance is a remarkable illustration of the 

 changes which are effected under the influence of oxygen. 



Fig. 478. — A Sewage Fungus, 

 Beffguitoa alba (sulphur bac- 

 terium) 



a, In a medium rich in sul- 

 phuretted hydrogen. b t Almost 

 depleted of sulphur granules by 

 twenty-four hours' immersion 

 in water free from sulphur, 

 c, Sulphur disappeared ; trans- 

 verse walls now visible, after 

 forty-eight hours' further im- 

 mersion. </, Decaying through 

 lack of sulphuretted hydrogen. 



