BY EDWIN H WILKINSON. 



101 



it is, indeed, difficult to describe the'm la 

 popular language. They vary in length 

 from one-five thousandth to one-twenty- 

 five thousandth of an inch. When view- 

 ed under the most powerful microscopes 

 they appear to be a little larger than dots 

 of ink on paper. "If," say Pearman and 

 Moore in their work on ''Applied Bacteri- 

 ology/' ''we could view an average human 

 being, under an equal degree of magnifi- 

 cation, he would appear to be about four 

 miles in height." 



In a volume equal to the GGth part of a 

 grain, Bujivid estimated no less than eight 

 thousand millions of microbes. 



With reference to the incredible rapid- 

 ity with which the bacteria multiply un- 

 der conditions favourable to their growth 

 and development, Cohn writes as follows: 

 — "Let us assume that a microbe divides 

 into two within an hour, then again into 

 eight in the third hour, and so on. The 

 number of microbes thus produced in 2i 

 hours would exceed 16^r millions; in two 

 davs they would increase to 47 trillions: 

 and in a week the number expressing them 

 would be made up of 51 figures. After 24 

 hours the descendants from a single bacil- 

 lus would weigh l-26661b.; after two days 

 over a pound; after three days. 7,366 tons. 

 It is quite unnecessary to scate that these 

 figures are purely theoretical, and could 

 only be attained if there were^no impedi- 

 ments to such rapid increase.'' 

 • "Fortunately for us," observe Messrs. 

 Pearman and Moore, "various checks, 

 such as lack of food and unfavourable 

 physical conditions, prevent unmanage- 

 able multiplications of this description. 

 Naturally the question will at once arise 

 as to what becomes of the dead bodies of 

 those bacteria which succumb in the 

 struggle for existence. A dead bacterium 

 is only so much food for his friend, who 

 evidently considers that all is fish that 

 comes to his net." 



The figures given fthow what a tremen- 

 dous vital activity niicro-organigms or 

 "bacteria" possess, and it may be seen at 

 what speed they can increase in water, 

 milk, broth, yeast, and other =nitable and 

 nutrient media. You can realise from the 

 foregoing remarks the enormous force 

 which the sanatarian has at his disposal 

 for the rapid and effectual destruction of 

 tvaste animal and vegetable matters by 

 the action of the life processes of these 

 minute scavengers, provided that the con- 

 ditions of their environment are carefu-Uy 

 arranged, so as to afford them the freest 

 possible scope. 



If any porous material, such as coke 

 breeze, "^burnt clay, etc., be placed in a 

 vessel or tank, and sewage water admit- 

 ted thereto, a large proportion of the filth 

 contained therein will adhere to the rough 

 sides of the coke or other material, and 

 the organisms will commence their work 

 Ijy feeding and multiplying so that in a 



short time the whole surface of each par- 

 ticle of coke or other material which may 

 be employed, will be covered with them. 

 Let the water be drawn off gently, after 

 sufficient time has been allowed for the 

 adherence of the fine particles of matter 

 to the coke. Air will be admitted as the 

 water is lowered, and a fresh impetus will 

 be given to the little workers, who will 

 soon be ready for another supply of food 

 to be given to them in the form of a se- 

 cond quantity of foul water. The organ- 

 isms at work'uuder circumstances such as 

 these are the serobic microbes previously 

 described. The anaerobic do not depend 

 on the air for their existence, and it is 

 this class that carries on the purification 

 process in what are known as septic tanks. 

 It will be seen these processes may con- 

 tinue indefinitely, and that we can bring 

 about the destruction of objectionable 

 matters completely and economically for 

 as long a time as may be desired. 



Such, then, is Nature's method of puri- 

 fication. 



The process is termed biological, but it 

 must not be supposed that because this 

 term is used in reference to the treatment 

 of sewage, it is intended to imply that 

 (he micro-organisms are provided by 

 the bed itself, and that the sewage does 

 not contain them. The organisms are to 

 be found in all sewage, and they are by 

 the sewage conveyed into the beds, where 

 large surfaces are provided, and on which 

 the bacteria are cultivated. 



Having, with these few introductory re- 

 marks, given an idea of the great activity 

 of micro-organisms, and of their enormous 

 power in working out purification of sew- 

 age, it will perhaps be interesting to hear 

 of what is being done with their assist- 

 ance in a few of the more important cities 

 of the United Kingdom. 



For much of my information on this 

 subject I am indebted to Mr. J. Davis, 

 M.I.C.E., late Engineer-in-Chief of the 

 Sewerage Construction Branch of the Pub- 

 lic Works Department of New South 

 Wales, who last year presented his report 

 to the Minister for Public Works on the 

 "Latest Methods in use^ in the United 

 Kingdom and elsewhere." 



In order that we may start at the be- 

 ginning I shall first deal with Scott-Mon- 

 crieff's methods. _ ,, ^_ 



It appears that Mr. W. D. Scott-Mon- 

 crieff commenced his experiments on a 

 practical scale in 1891. He erected what 

 he called a "cultivation tank," measuring 

 2ft. 9in. wide, 10ft. long, and 3ft. deep 

 at the deepest end. Excluding the grease 

 by means of a trap, he allowed the entire 

 sewage and waste water from one dwelling 

 house to enter the tank at the lowest end. 

 The sewage passed through a perforated 

 plate, which was fixed about one foot from 

 the bottom of the tank. Underneath this 

 plate the solids were arrested. Above the 



