FOOD 



129 



i/lobator (fig. 482), has on certain occasions appeared in enormous quantities 

 in the reservoirs which supply Rochester in the State of New York, 

 imparting to the water a fishy taste and odour, and apparently causing 

 sickness and death among the cattle which drank it. The stoneworts 

 (fig. 483), so called from becoming coated over with an earthy deposit, 

 when existing in large quantities give off sulphuretted hydrogen, which 

 is a highly poisonous gas. A variety of fresh-water sponge has been iden- 

 tified as giving a nauseous odour and taste to water, owing to the presence 

 of ammonia. Its removal from the places in 

 which it grew was followed by the restora- 

 tion of the water to a wholesome condition. 



Mr. Francis, of Adelaide, records that 

 in 1878 the lakes which form the estuary 

 of the Murray contained a plant which he 

 believed to be allied to the Protococcus, 

 which formed a thick scum like green paint, 

 some 2 or 3 inches thick, on the surface of 

 the water, and when swallowed by cattle, 

 which drank of it, it rapidly caused death. 



Numerous other instances might be re- 

 ferred to in proof of the fact that while 

 certain plants, probably without exception 

 all flowering plants, and to a large extent 

 all the high order of green plants which 

 flourish in water and give out oxygen, par- 

 ticularly during the daytime and when the 

 sun is shining, exercise a purifying influence 

 upon water, there are others, including a 

 number of aquatic fungi, which either exer- 

 cise an injurious influence or indicate by 



their presence that the water is unfit for use. It is, therefore, a matter 

 of considerable importance that the very common procedure of weed- 

 cutting should be exercised with discrimination. All the aquatic plants 

 which are beneficial, as well as those which are injurious, to water, are 

 distinguished by botanical characteristics which can be readily identified by 

 an expert. There will be no real difficulty, therefore, in determining, at 

 any rate within certain reasonable limits, what plants should be as far as 

 possible extirpated and which of them should be allowed to flourish. 



Examination of Water. — In works on hygiene which are exclu- 

 sively intended for professional readers it is usual to describe the processes, 

 both chemical and physical, for the analysis of water for the purpose of 



Fig. 483. — Stonewort (Chara fragilis) 



1, Plant. 2, Sporangium and anther- 

 idium. 3, Valve of antheridium. 4, 

 Enlarged branch. 5, Section of spor- 

 angium. 6, End of a filament. 



Vol. III. 



74 



