1893.] MICROSCOPICAL JOURNAL. 187 



l)c as (.-asiK rccoj^iiizcd as arc other siil)staiiccs susceptible of 

 definite microscopical detei ininatioii. 



Hut this is not all. The researches of I'rof. I'idy in Eiij^land 

 and of Dr. Drown in this country have shown that sewaj^e. when 

 dischar<;ed into a stream, and especially into a slu^j:jish flowing 

 one, not oidy cpiickly removes the dissolved oxygen, hut its eflect 

 is, further, such as to keep the oxygen permanently, nearly, or 

 actually //// near the bottom.* Deposited sewage may. therefore, 

 remain at the bottom of a polluted stream for months almost 

 without change, and may be. by the use of the microscope, iden- 

 tified as such through the medium of the methcnl here discussed. 

 Thus far two English microscopists, namely, Drs. Beale and 

 .Sorby, are about the only persons to pursue this line of study to a 

 really practical conclusion. A paper by Dr. IJeale may be found 

 in the journal of the Royal Microscopical Society tor February, 

 iSS4.t In it Dr. Beale gives in detail the method of examining 

 sewage muds which he puisued i.i the case of twenty-five samples 

 from the Thames' mud banks, together with the more important 

 results which he obtained. His results are (jualitative purely. 



Dr. Sorby about the same time worked out a method of quan- 

 titativel}- determining by the use of the microscope the amount of 

 the fixed constituents of sewage in a given volume of water and 

 applied it in an elaborate investigation of the pollution of the 

 river Thames, undertaken at the instance of what is known in 

 sanitary literature as the Royal Commission on Metropolitan 

 Sewage Discharge of 18S4.:}: In his communication to that com- 

 mission Dr. .Sorby gives in great detail the results of a large num- 

 ber of determinations of the fixed constituents of human excre 

 ments, as foimd in samples of Thames' water taken at different 

 stages of the flow. Rather curiously, however, he fails to point 

 out just the method pursued in olitaining his quantitative results, 

 and in consecjuence the work has never received the attention 

 which its importance would otherwise havesecured for it. Never- 

 theless Dr. Sorby's great reputation as a working microscopist 

 may lead us to accept his results as essentially correct, even 

 though w^e lack the detail of the method pursued. Some of his 

 more important conclusions may be briefly stated as follows : 



(i) There is no serious difficulty in determining with the 

 microscope the relative amount of human fteccs or of horse 

 manure from street washings in any given sample of water or de- 

 posit of mud. 



(2) The moderately fine portion of human faeces, amounting 

 to about 31 per cent, of the whole, is the portion which yields 

 the greatest amount of valuable information. This portion con- 



* For a recent exposition of this part of the subject see as follows : (i) On the Amount of 

 Dissolved Oxygen contained in Waters of Ponds and Reservoirs at Different Depths ; and (2) 

 The Effect of the Aeration of Natural Waters, both by Dr. Thomas M. Drown. 23d An. Rept. 

 Mass. St Bd. Hc;<lili (1S91), pp. 373-394. 



t The Constituents of Sewage in the Mud of the Thames. By Dr. Lionel S. Beale. 



J See volume ii, Rept. of Roy. Com., etc., Report of Microscopical Investigation, with 

 detailed result-, by Dr. H. C. Sorby, pp. 169-184. 



