146 BACTERIA IN THE SOIL 



as the " critical " 4-foot earth temperature, that is to say, the 

 temperature at which certain changes (putrefactive, bacterial, etc.) 

 take place either, primarily, in the earth, or secondarily, in the atmo- 

 sphere, with the consequent development of the diarrhoeal poison. 



After prolonged investigation on behalf of the Local Govern- 

 ment Board, Dr Ballard formulated the causes of diarrhoea in the 

 following conclusions : — * 



(a) The essential cause of diarrhoea resides ordinarily in the super- 

 ficial layers of the earth, where it is intimately associated with the 

 life processes of some micro-organism not yet detected or isolated. 



(&) That the vital manifestations of such organism are dependent, 

 among other things, perhaps principally upon conditions of season 

 and the presence of dead organic matter, which is its pabulum. 



(c) That on occasion such micro-organism is capable of getting 

 abroad from its primary habitat, the earth, and having become ah'- 

 borne, obtains opportunity for fastening on non-living organic 

 material, and of using such organic matter both as nidus and as 

 pabulum in undergoing various phases of its life-history. 



(d) That from food, as also from contained organic matter of 

 particular soils, such micro-organism can manufacture, by the 

 chemical changes wrought therein through certain of its life 

 processes, a substance which is a virulent chemical poison. 



Here, then, we have a large mass of evidence from the data . 

 collected by Buchanan, Bowditch, Pettenkofer, and Ballard. But 

 much of this work was done anterior to the time of the application 

 of bacteriology to soil constitution. Eecently the matter has 

 received increased attention from various workers abroad, and in this 

 country from Eobertson, Martin, Houston, and others, and we must 

 now consider the new facts brought forward by these investigators. 



From the first, experiments on this subject have been more or 

 less confined to the behaviour of the typhoid bacillus than any other 

 pathogenic organism. This has been partly due to the importance 

 of this organism in relation to soil, and partly because it is more 

 convenient than, say, the tubercle bacillus for experimental work. In 

 1888 Grrancher and Deschamps showed that the typhoid bacillus was 

 able to survive in soil for more than twenty weeks,f and Karlinski 

 arrived at a similar conclusion. | In 1894 Dempster published the 

 results of his work on the same subject, in which he obtained the 

 typhoid bacillus from sand after twenty-three days, from garden soil 

 after forty-two days, and from peat not later than twenty-four hours. § 

 Four years later came Dr Eobertson's valuable researches into the 



* Supplement io the Report of the Medioal Officer of the Local Oovernment Board, 

 1887, p. 7. 



t Arch, de Med. Exp. et d'Anat. Path., 1889, 7th January. 

 t Arch. f. Eyq., Bd. xiii., Heft 3. 

 § Brit. Med. Jour., 1894, i., p. 1126. 



