58 



KNOWLEDGE 



[March 1, 1894. 



Mr. Laws remarks, to become contaminated in every 

 possible way. One important peculiarity of this sewer is 

 that no lateral sewers or house drains enter it from one 

 end to the other, and that it is freely ventilated to the air 

 of the park. In length it is about three hundred yards ; 

 it is barrel-shaped, about eleven feet high and nine feet 

 wide, and is ventilated by open gratings in the crown of 

 the sewer. These open gratings could be closed for the 

 purposes of experiment, and sewage matter could be 

 poured through them at various distances from the 

 experimenter, so as to imitate as nearly as possible the 

 splashing and disturbing effect of matter entering a sewer 

 fi-om a house at a known distance. A wooden staging was 

 erected across the sewer, near to one of the entrances, from 

 which the experiments were made. 



Mr. Laws adopted the following process for determining 

 the number of micro-organisms in the air. A known 

 quantity of air was aspirated through a sterile tube, con- 

 taining two sterile plugs composed of powdered sugar and 

 glass wool. These plugs, which filter the air, were, after 

 the completion of the experiment, transferred to two 

 circular cultivating plates covered with nutrient gelatine 

 in a liquid state ; after careful mixing with a sterilized 

 platinum needle, the gelatine was allowed to solidify by 

 cooling. Each organism, therefore, becomes fixed, and 

 if capable of growing in the medium it forms a colony, 

 which, after the lapse of four to six days, is evident to the 

 naked eye. In almost every case the colony consists of a 

 pure growth of one species only. These colonies were 

 examined microscopically, and re-sown in sterile culti- 

 vating tubes, containing nutrient gelatine or agar-agar, for 

 further study. 



In a report '■' to the London County Council, recently 

 issued, Mr. Laws gives a list of the micro-organisms 

 detected by him in the air of the sewer above-mentioned 

 as well as in the air of other sewers. All the micro- 

 organisms tabulated by him belong to the class known as 

 non-pathogenic — that is, they are harmless bacteria — and, 

 with one exception, they are species commonly found in 

 air and water. 



He says : "There are two points with reference to the 

 organisms in sewer air to which I wish to call special 

 attention — firstly, the absence of bacillus roli communis and 

 micrococcus urea, two organisms which must be present in 

 sewage in immense numbers ; secondly, the almost entire 

 absence of any organisms capable of very rapidly liquefying 

 gelatine, the only exceptions being the common hay 

 bacillus (liacilhis snhtilis) and a micrococcus mentioned in 

 my first report. In sewage, on the other hand, a large 

 number of organisms, for the most part bacilli, possess this 

 property of very rapidly liquefying gelatine." 



In the splashing experiments conducted in the King's 

 Scholars Pond sewer, Mr. Laws found that when the 

 splashing was sufficiently violent to produce a very fine 

 state of division of the sewage, organisms from the sewage 

 were occasionally carried to a distance of from fifty to sixty 

 yards ; but, as a general rule, there is comparatively little 

 draught in the sewers, and the particles are carried no great 

 distance, and quickly subside again into the sewage at the 

 bottom, or are caught on the wet walls of the sewers, and 

 Mr. Laws found that, as a general rule, a decrease in the 

 number of organisms in the fresh air above ground was 

 followed by a decrease in the number of micro-organisms 

 in the sewer air. 



These espeiiments entirely sweep away the theory that 



* "Report to tlie Main Drainage Committee of the London County 

 Comieil on Sewer Air Investigations," by ,1. Parrv J.aivs, F.I.C. 

 Steel and .Jouc.-, 4, Spring Gardon?, S.AA' Trici' (id. 



zymotic diseases are spread by micro-organisms carried by 

 sewer air. It may be regarded as demonstrated beyond 

 dispute, that certain kinds of micro-organisms invariably 

 accompany certain diseases, and reproduce similar diseases 

 when introduced by inoculation into the bodies of men or 

 animals, even after one or more generations of such 

 organisms have been grown in sterilized media. So that 

 such diseases must be produced by the micro-organism, and 

 not by any organic matter or product of putrefactive 

 decomposition allied to the dangerous class of poisons 

 known as ptomaines. 



But as far as infection by micro-organisms is concerned, 

 it seems that the sewer rats have more reason to complain 

 of our ventilating their homes with the bacteria-laden 

 upper air than we have to complain of infection by micro- 

 organisms carried by sewer air into our streets and houses. 

 In a matter of such great importance, involving risks of 

 life, and — what is even of more importance — involving 

 the healthy condition, happiness, and working power of 

 milhons, we must proceed with all scientific caution, and 

 must not conclude without prolonged further investigation 

 that sewer air is not injurious. It may have an indirect 

 effect in lowering our vital power and rendering us more 

 liable to the attacks of micro-organisms derived from 

 other sources. 



We have at present very few accurate statistics to go 

 upon, but general observations seem to show that the men 

 who work in sewers are not more subject to zymotic 

 diseases than other classes of the community — in fact, 

 they seem to be rather less subject to them — and the 

 children of the sewer-men, who live at the outfall works 

 and who spend a great deal of their playtime upon the 

 ventilating grids of the sewers, seem to be very healthy 

 little creatures. As far as I can learn, there has been no 

 recent outbreak of zymotic disease amongst them, while 

 the rest of London has been passing through a long 

 period of feverish anxiety, and the permanent hospitals 

 and temporary fever hospitals have been crowded to over- 

 flowing with infectious patients. 



I have made what inquiries I can from Mr. Laws, and 

 others who have come into contact with workers in sewers, 

 to find what precautions the sewer-men take before they 

 eat their dinners. I am informed that much of their 

 work involves the plunging of their hands into offensive- 

 looking sludge, but it is only the more fastidious of them 

 who carry a rag or a handful of cotton waste in their 

 pockets, with which they give their hands a rub before 

 they sit down to eat. The rest, perhaps, give their hands 

 a rub on their trousers or coat, and set to work at their 

 food at once, without carefully cleaning their nails, or 

 washing their hands with disinfectants, as a doctor would 

 think necessary under similar circumstances, and yet these 

 men are comparatively healthy, and, if anything, are less 

 subject to zymotic diseases than their neighbours. Such 

 facts would almost lead one to doubt whether our theories 

 as to infection by sewage, and our dread of a whiff of 

 sewage air, may not be as mistaken as the superstitious 

 belief of the savage in the protecting power of his amulet, 

 or as unfounded as his terror of the evil eye. 



But we must proceed cautiously if we wish to follow the 

 scientific method, and must remember (as Mr. Charles 

 Booth, the present President of the Statistical Society, 

 forcibly pointed out in a very interesting address, delivered 

 in November last, on the results of the census of 1891 

 with regard to the statistics of life and labour in London), 

 that the results which the statician offers us need to 

 be very carefully analyzed before we dare to found exten- 

 sive theories upon them. To form a sure foundation for 

 1 reasoning by the inductive method, we need a series of 



