1893.] MICROSCOPICAL JOURNAL. l.U 



studied in considerable detail. The tollowintj statement of or- 

 <;anisnis in Lake Cochituate, one of the sources of supplv to that 

 citVi is based u|)on weekly observations f(jr two years, and gives 

 a list of the predominant organisms with the number per icx) 

 cubic centimetres sometimes reached or which may be commonlv 

 looked for :* 



Asterionella . . . 200,000 Anabiena (sterile) i-{,(XXi 



Tabellaria . . . 100,000 Cyclotella .... 10.000 

 Melosira .... 75,000 Microcystis .... 5,000 



Prott)Coccus .... 30,000 Monas 5,000 



Synedra .... 25,000 Cadospha-rium . . 2,500 

 Crenothrix .... 20,000 Clotliroc\ stis . . . 2,500 



In the foregoing is set forth some of the residts attained bv use 

 of the new method of quantitative enumeration of the microscopi- 

 cal forms present in potable water. Let us now brieflv examine 

 another j)hase of the cjuestion. 



At the present time the development of new and more exact 

 methods of water analysis has produced, in matteis relating to the 

 conservation of public water supplies, what mav be termed a 

 transition state, in which the progressive movement is, as we 

 have already seen, clearly in the direction of a study from every 

 possible point of view, rather than from one or two, as has been 

 until recently almost universally the case ; this cliange is so marked 

 that a review of some phases of the advance in methods of study- 

 ing the sanitary value of potable water may be profitably made. 



It is to England that we are chiefly indebted for the most of 

 our early knowledge of the sanitary properties of water. The 

 large amount of work in the way of study of the pollution or 

 streams by sewage and manufacturing which has been accom- 

 plished there within the last fifty years has easily placed Eng- 

 land first in the list for improvements in this branch of sanitary 

 knowledge. In proof of this we have only to consider (i) that, 

 until within the last decade, chemical analysis has furnished the 

 only scientific method of assisting judgment in the selection of 

 the source of a public water supply ; and (2) that of the three 

 methods of chemical analysis which have been generally used, 

 two, at any rate, are purely English developments, while the third, 

 though originating elsewhere, has perhaps received its most ex- 

 tensive application in the hands of an eminent English chemist. 

 The three systems of chemical analysis which are here referred 

 to are the '■ albimiinoid ammonia jjrocess" of Wamklyn, 

 Chapman tS: Smith, the '' combustion process" of Franklin iv: 

 Armstrong, and the "■ permanganate process" of Forchhammer, 

 which in England has been adopted and extensively uSed by Dr. 

 Tidy. All of them have been developed and reduced to practical 

 value within the last twenty-five to thirty years. Previous to that 

 time, about all attempted in water analysis was the determination 



* Sixteenth .An. Rept. o( the Boston Water Hoard for the 13 months endiog Jan. 31, 1892,9. 66. 



