1894.] MICROSCOPICAL JOURNAL. 377 



A Standard Unit of Size for Micro-Organisms. 



By GEORGE C. WHIPPIvE, 

 BIOLOGIST, BOSTON WATER WORKS. 

 WITH FKOKTISPIECE. 



The Sedgwick-Rafter* method of microscopically ex- 

 amining water is now in quite general use. Experience 

 has proved that it is a most satisfactory and valuable 

 means of studying the micro-organisms found in water. 

 But in spite of the excellent precisionf of the methods, 

 the results of the examinations as they are generally 

 stated are sometimes quite misleading ; that is, they do 

 not always correctly represent the amount of animal and 

 plant life present in the water. It has usually been the 

 custom of biologists to record the number of organisms 

 present in a cubic centimeter of the water examined, 

 without regard to their character or size ; single cells, 

 filaments, colonies, irregular masses have been counted 

 as units and the same value assigned to each. 



This was the method first used in the Biological Lab- 

 oratory of the Boston Water Works. The results were, 

 in some respects, unsatisfactory. When one compared 

 the number of organisms found at the different seasons 

 of the year it was found that the largest numbers did not 

 occur at the times when the water, judged by its appear- 

 ance, taste and odor, was manifestly the poorest. 



Furthermore, the microscopical results did not always 

 compare well with the chemical analyses. This was 

 found to be largely due to the different sizes of the or- 

 ganisms. Coelosphaerium, for instance, was found to 

 contain more than a thousand times as much organic 



*W. T. Sedgwick. — Reyiort of the Biological Work of the Lawrence Experiment station. Spec- 

 ial Report of the Massachusetts State Board of Health on the Purification of Sewage and water 

 1890. 



Geo. W. Rafter. — The Microscopical Examination of Potable Water. Van Nostrand Science 

 Series, No. 103. 



+Gary N. Calkins. — The Microscopical Examination of Water, 23rd Annual Report of the 

 Massachusatts State Board of Health, 1891. 



