BACTERIA IN THE SOIL 175 



third series of investigations concluded in the same direc- 

 tion, viz., the researches of Dr. Ballard respecting summer 

 diarrhoea. This, it is generally held, is a bacterial disease, 

 although no single specific germ has been isolated as its 

 cause. Ballard demonstrated that the summer rise of diar- 

 rhoea mortality does not commence until the mean temper- 

 ature of the soil, recorded by the four-foot thermometer, 

 has attained 56.4 F., and the decline of such diarrhoea 

 coincides more or less precisely with the fall in soil temper- 

 ature. This temperature (56.4 F.) is, therefore, considered 

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

 say, the temperature at which certain changes (putrefactive, 

 bacterial, etc.) take place in the pores of the earth, with the 

 consequent development of the diarrhceal poison. 



After a very elaborate and prolonged investigation on be- 

 half of the Local Government Board, Dr. Ballard formulates 

 the causes of diarrhoea in the following conclusions: l 



(a) The essential cause of diarrhoea resides ordinarily in 

 the superficial layers of the earth, where it is intimately as- 

 sociated 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 mat- 

 ter, 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 air-borne, obtains opportunity for fastening 

 on non-living organic material, and of using such organic 



(d) a specific micro-organism in the soil. These four conditions have not, par- 

 ticularly in England, always been fulfilled preparatory to an epidemic of 

 typhoid. Yet the observations necessary for these deductions were a definite 

 step in advance of mere dampness of soil. 



1 Supplement to the Report of the Medical Officer of the Local Government 

 Board, 1887, p. 7. 



