94 MANUAL OF POISONOUS PLANTS 



The majority of organisms which have been recorded are of microscopic size. At first 

 sight it might appear that these organisms would be insignificent in proportion to their mass, 

 and that more attention should have been devoted to the larger plants and animals. Very 

 few cases have been observed, however, in which really serious trouble in water supplies 

 can be referred directly to the growth of large plants or animals; whereas, in many in- 

 stances, waters with very objectionable qualities contain nothing to which these qualities 

 can be attributed except microscopic organisms. Further, although the organisms here dealt 

 with are of such small dimensions, the immense numbers in which they occur more than 

 counterbalance their small size; and I am therefore, of the opinion that, of those organisms 

 which cause objectionable qualities in water, the microscopic ones are the more important. 



HOW GROWTH OF ALGAE IN WATER MAY BE PREVENTED 



The growth of algae may be prevented by covering the reservoir ; since 

 light is essential for their growth, they will not develop in a closed reservoir, 

 and we hear of little complaint under such conditions. Large reservoirs for 

 public water supplies are not generally covered. Often reservoirs are much 

 troubled by algal contamination; in some cases it becomes necessary to remove 

 these by a laborious method. The removal of organic matter by keeping the 

 source of the water supply in as pure condition as possible will no doubt do 

 something toward keeping algae out, but nearly all water contains sufficient 

 organic matter for the growth of algae, especially water coming from water 

 sheds. 



THE USE OF ALGICIDES 



Within recent years much work has been done in preventing the growth 

 of algae and bacteria by copper sulphate solutions. Moore and Kellerman in 

 a recent paper arrive at the following conclusions : 



The disagreeable odors and tastes so often present in drinking water are due almost 

 exclusively to algae, although the economic importance of studying these plants has not been 

 recognized until recent years. These algal forms are widely distributed, and reservoirs in 

 many states have been rendered unfit for use by their presence. It has been found that 

 copper sulphate in a dilution so great as to be colorless, tasteless, and harmless to man is 

 sufficiently toxic to the algae to detroy or prevent their appearance. At ordinary temper- 

 atures one part of copper sulphate to 100,000 parts of water destroys typhoid and cholera 

 germs in from three to four hours. The ease with which the sulphate can then be elimin- 

 ated from the water seems to offer a practical method of sterilizing large bodies of water 

 when this becomes necessary. The cost of material for exterminating algae will not exceed 

 fifty to sixty cents per million gallons and will usually be less. The destruction of patho- 

 genic bacteria requires an expenditure of from $5.00 to $8.00 per million gallons, not 

 including the cost of labor. 



It has been found that Spirogyra will die in water containing one part of 

 copper to one billion parts of water. Some of the algae like Anabaena are 

 destroyed in dilutions from one to five million, although Moore and Kellerman 

 found that one species of Spirogyra requires a greater strength of solution. 

 There is a wide-spread opinion that metallic copper and copper salts are in- 

 jurious, which is certainly true when the same are taken in larger quantities. 

 According to Tschirsch, .05 to .2 of copper sulphate causes vomiting and diar- 

 rhoea. In the paper cited, Moore and Kellerman write as follows : 



It is evident that there is still a considerable difference of opinion among eminent 

 authorities as to the exact amount of copper which may be injurious, but as a very con- 

 servative limit we may accept 0.02 gram as the amount that may with safety be absorbed 

 daily. According to Merck's Index, the National Dispensatory, and the United States 

 Dispensatory, the dose of copper sulphate for tonic and astringent purposes is one-fourth 

 grain, or 0.016 gram; as an emetic, a dose of five grains, or 0.33 gram. Thus it is seen 

 that even if the maximum concentration of copper sulphate necessary to destroy algae in 

 reservoirs were maintained indefinitely, the absorption from daily use would be very far 

 below an amount that could produce the least unpleasant effect. Taking a dilution of one 



