148 BACTERIA IN THE SOIL 



Lastly, we have the results of the investigations of Firth and 

 Horrocks, who conclude that the typhoid bacillus is able to assume a 

 vegetative existence in ordinary soils and in sewage-polluted soils for 

 as long as seventy-four days. They further maintain that the 

 controlling factor is an excess or deficiency of moisture in the soil 

 rather than organic nutritive material. From dry fine sand the 

 bacillus was recovered after twenty-five days ; from moist fine sand, 

 after twelve days ; from damp (rain-water) ordinary soil, after sixty- 

 seven days ; from damp (sewage) ordinary soil, after fifty-three days ; 

 and from ordinary soil dried to the state of dust, after twenty-four 

 days. In peat the bacillus lives apparently only a few days.* Firth 

 and Horrocks, therefore, arrive at a different conclusion from Martin, 

 namely, that the typhoid bacillus is able to assume a vegetative or 

 saprophytic existence for considerable periods outside the body; that 

 it can survive ordinary earth for over two months, whether the soil be 

 virgin or polluted with sewage, or frozen hard ; and that, therefore, it 

 follows that outbreaks of enteric fever may be due to the dissemina- 

 tion (for example by wind or flies) of infective soil dust. Pfuhl of 

 Berlin has arrived at results confirmatory of these experiments. 

 From moist garden earth he recovered the typhoid bacillus eighty-eight 

 days after inoculation, from dry sand after twenty-eight days, and 

 from moist peat twenty-one days.")* 



On the whole it would appear that whilst much valuable research 

 has been accomplished, it cannot be said that the relation of the 

 typhoid bacillus to soil is understood. Some further light on the 

 subject is obtained from researches carried out in relation to the 

 bacterial condition of sewage-treated land and made-up refuse soil, 

 and brief reference may be made to such work. 



Various workers have carried out experiments with the object of 

 ascertaining whether in the surface layers of soil, after it has had 

 sewage upon it, certain microbes characteristic of sewage retain their 

 vitality for any considerable length of time ; what, in short, was the 

 fate of such organisms as B. coli, B. enteritidis sporogenes, etc., when 

 sown broadcast on soil. For if their fate be known, not only would 

 light be thrown upon questions of sewage treatment, and the pollu- 

 tion of soil which might in turn affect water supplies, but indication 

 would be obtained as to the possibility of disease germs maintaining 

 their existence in soil, and eventually infecting man. Chief among 

 such investigations in England have been those of Dr A. C. Houston,! 

 whose conclusions are briefly as follows : 



(1) The addition of sewage to an ordinary garden soil does not 



* Brit. Med. Journ., 1902, ii., pp. 936-943. 

 t Zeti. f. Hyg., 1902, Bd. xl., Heft 3, p 555. 



$ Report of Medical Officer to Local Government Board, 1900-01, App. No. 4, 

 p. 405 ; 1901-02, App. No. 6, p. 455. 



