1802.] MICBOSCOPICAL JOURNAL. 5T 



Mr. Hogg in the tenth edition of his work on the microscope has 

 added a chapter on the microscopical examination of potable water, 

 hut without advancing any methods other than those previously 

 announced by McDonald. Likewise Tiemann and Giirtner, the recent 

 German authorities, have added nothing to our knowledge of this part 

 of the subject. 



The matter of qualitative examination of the micro-organisms in 

 potable water remained in about the state indicated by the foregoing 

 until a little less than a year ago. when Prof. Wm. T. Sedgwick, of the 

 Massachusetts Institute of Technology, worked out a method for 

 making the quantitative determination as well.* This consists, lirst, in 

 the concentration of the organisms from a large amount of water into 

 so little water that they nia}' be readily examined under the conditions 

 imposed by microscopical technique ; and, second, of an actual enu- 

 meration of all the organisms present in a given quantity of water. 

 The first point is attained by filtration through a short column of fine 

 sand in the lower end of the stem of a small funnel, the sand being sup- 

 ported upon some material which will allow the water to pass freely 

 and still retain the sand in position. After placing the sand, a measured 

 quantity of water is poured into the funnel and allowed to filter through. 

 The sand retains nearly all the organisms which were originally 

 distributed through the water. The enumeration is secured, according 

 to Prof. Sedgwick, by removing the supporting plug and washing the 

 sand and contained organisms into a cell, 50 x 20 millimetres in' area, 

 and about 2 to 2^ millimetres in depth. The glass bottom of this cell 

 is ruled into square millimetres, and by passing a number of these 

 squares through the field of a microscope their contents are counted 

 and from the counts so made the whole number present in the cell is 

 obtained. This method while far in advance of that of McDonald is 

 still somewhat unsatisfactory in this, that the sand and organisms are 

 both allowed to pass into the cell together, and inasmuch as the finest 

 grains of sand are much larger than many of the organisms, it follows 

 that the enumeration, however carefully made, is only a rough approxi- 

 mation to the number actually present, and usually falls short of the 

 number actually present. 



The method of Prof Sedgwick came to my notice about nine months 

 ago, and after examination it appeared quite evident that considerable 

 additional refinement was possible, and to this I addressed myself with 

 the result of finally perfecting the technique in the manner which I now 

 briefly lay before you. 



In the method, as I now use it, the sand is supported upon a plug of 

 wire cloth placed at the lower end of the funnel stem, as shown on 

 page ^6. After placing the plug the sand is run into the funnel, lightly 

 pressed to place with a glass rod, and from 20 to 40 c.c. of freshly- 

 filtered water allowed to run through in order to insure thorough set- 

 tling of the sand before actually beginning the filtration. The amount 

 of water to be filtered is gauged by the number of organisms which it 

 contains, as ascertained by preliminary inspection. Generally, how- 

 ever, as large a quantity should be used as can be conveniently filtered 

 without clogging the sand so much as to render the completion of the 



*See paper on Recent Progress in Biological Water Analysis in Transactions of New England 

 Water-Works Association, September, 1889. 



