RELATION TO DISEASE 145 



to the development of the cholera spirillum, and under ordinary 

 circumstances it succumbs in the struggle for existence. Other 

 species of bacteria have also been isolated from soil from time to 

 time. 



Now whilst since the early days of bacteriology the three organ- 

 isms we have described have been looked upon as the typical bacteria 

 of soil, modern research has brought to light a new relationship 

 between soil and disease, which has greatly enhanced the importance 

 of our knowledge of the subject. Directly, it has been shown that 

 soil may harbour germs of disease, acting sometimes as a favourable 

 and at other times as an unfavourable nidus. Indirectly, it has been 

 shown that a right understanding of the bacteriology of water arid 

 its potentiality of disease production, depends upon a knowledge of 

 bacteria in the soil over, or through which, the water has passed. 

 The matter must, therefore, be briefly considered here. 



The Relation of Soil generally to certain Bacterial Diseases 



It is now some years since Sir George Buchanan, for the English 

 Local Government Board, and Dr Bowditch, for the United States, 

 formulated the view that there is an intimate relationship between 

 dampness of soil and the bacterial disease of Consumption (tuber- 

 culosis of the lungs). The matter was left at that time sub judicc, 

 but the conclusion has since been drawn, and it is surely a legitimate 

 one, that the dampness of the soil acted injuriously in one of two 

 ways. It either lowered the vitality of the tissues of the individual, 

 and so increased his susceptibility to the disease, or in some unknown 

 way favoured the life and virulence of the bacillus. That is one fact. 

 Secondly, Pettenkofer traced a definite relationship between the rise 

 and fall of the ground water with pollution of the soil and enteric 

 (typhoid) fever.* A third series of investigations concluded in the 

 same direction, viz., the researches by 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 diarrhoea mortality does not 

 commence until the mean temperature of the soil, recorded by the 

 4-foot thermometer, has attained 56 '4 F., and the decline of such 

 diarrhoea coincides more or less precisely with the fall in soil 

 temperature. This temperature (56*4 F.) is, therefore, considered 



* The conditions requisite for an outbreak of enteric fever were, according to 

 Pettenkofer, (a) a rapid fall (after a rise) in the ground water, (6) pollution of the 

 soil with animal impurities, (c) a certain earth temperature, and lastly (d) a specific 

 micro-organism in the soil. These four conditions have not, particularly 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 the idea of the 

 significance of mere dampness of soil. 



K 



