170 The Ottawa Naturalist [Feb. 



which have been stored. Such foods ma}' be and frequently 

 are consumed with fatal results. There is every reason to 

 believe that certain waters and rnore particularly stagnant 

 waters in which there is decaying vegetable and animal matter, 

 possess this poisonous property. Some of us may have experi- 

 enced the nauseating effects of water from a pond or lake contain- 

 ing the products of decaying algae It is scarcely necessary 

 to add that such water is unfit for consumption. Moving 

 water is, as a rule, free from this class of impurity. This is a 

 phase of the water question that has not received from sani- 

 tarians the attention it deserves, but I am convinced of its 

 importance in judging of the merits of a water for a city or house 

 supply. 



So far we have learnt that what we have to fear in our water 

 supplies, is, first, the presence of disease germs, due to contam- 

 ination with sewage, and secondly, those products of the decay 

 of organic bodies from certain classes of matter, excretal or 

 vegetable and which exert a toxic action on the system. A third 

 form of pollution met with is the waste waters of manufactories 

 which are run into the w r ater course without proper purification. 

 These refuse waters may contain organic or inorganic substances 

 detrimental to health. Fortunately in Canada this kind of 

 pollution is not often found, but in the protection of our lakes 

 and rivers legislation must take cognizance of it and the laws 

 preventing the discharge of such waste into possible sources 

 of water supplies rigidly enforced. 



In considering the role of rain and snow in Nature some 

 two years ago, we learnt two facts of a fundamental character. 

 The first was that the earth's moisture was in continual circu- 

 lation. The ascension of water in the form of vapour, due to 

 the heat of the sun, went on constantly, day and night, winter 

 and summer, from earth and water surface alike. Ice and 

 snow, as we saw, could be converted into vapour without visu- 

 ally passing through the liquid state. This vapour of water 

 ascends until it reaches the higher and colder strata of the atmos- 

 phere where it is condensed to fall as rain, hail or snow, accord- 

 ing to the atmospheric conditions prevailing at the time of the 

 precipitation. This process of evaporation and condensation 

 distillation, in fact is from the point of view we are considering 

 to-night one of the greatest importance, for it is primarily one 

 of purification. The sun, then, is the agent above all others 

 that renders it possible to obtain a wholesome supply of drink- 

 ing water, for the water in being converted into vapour leaves 

 behind all those substances mineral and organic which it 

 held in solution and descending gives us one of the purest forms 

 of water found in Nature. 



