13 



tion can replace. Thus I have little doubt that in two 

 rivers equally polluted, the one a torrent and the other 

 with sluggish waters, the fish would live much longer in the 

 one than they would in the other. But the contrary might 

 be the case with the human species, for any one would 

 naturally be tempted by the sparkling water of the torrent, 

 and if drunk before the dangerous properties had had time 

 to become consumed, consequences little dreamed of would 

 most probably be the result. 



It is in the summer, and particularly if it should be an 

 unusually hot one, that man and beast and fish life will 

 suffer most from the pollution of our rivers. The water 

 then is very low in our streams. At that period, therefore, 

 less surface exists for the development of the chlorophyl- 

 laceous growths, one of the means of their self-purification. 

 The same volume of sewage as in winter is mixed with a 

 greatly diminished volume of water, and therefore the 

 sewage pollution is stronger and more dangerous, also the 

 smaller volume of water flows less rapidly, and consequently 

 is not so thoroughly aerated ; and, besides, just at this time 

 the ova of the fish are coming forth, and, like the young of 

 every species, are less able to support an impure medium 

 of existence. Without doubt they also suffer from the 

 turbidity of the water intercepting the rays of light so 

 necessary to their healthy growth. 



Another question arises when the pollution of our rivers 

 is considered : what effect has the flesh of fish, not only in 

 a dying state, but even in a slightly sickly condition, upon 

 any individual when consumed as an article of food ? We 

 all know that the flesh of salmon, when out of season, is 

 not only unpalatable, but dangerous if consumed in a large 

 quantity : I remember a case where the eating of a portion 

 of a spent fish caused vomiting, accompanied by diarrhoea. 



