310 BACTERIA AND DISEASE 



manure (Waldo). (5) The influence of the soil is a decided one. 

 Where the dwelling-houses of a place have as their foundation solid 

 rock, with little or no superincumbent loose material, the diarrhoeal 

 mortality is, notwithstanding many other unfavourable conditions 

 and surroundings, low. On the other hand, a loose soil is a soil on 

 which diarrhoeal mortality is apt to be high (Ballard). The pollution 

 of soil is probably the important element in the causation of diarrhoea 

 in towns on pervious soils. (6) Given two towns equally placed so 

 far as social and sanitary conditions are concerned, their relative 

 diarrhoeal mortality is proportional to the height of the temperature 

 and the deficiency of the rainfall in each town, particularly of the 

 third quarter of the year." 



Dr Newsholme concludes that " the fundamental condition favour- 

 ing epidemic diarrhoea is an unclean soil, the particulate poison from 

 which infests the air and is swallowed, most commonly with food, 

 especially milk." In other words, epidemic diarrhoea is a so-called 

 " filth-disease," preventable by improved sanitation in the broadest 

 meaning of the term.* 



From the facts and suggestions quoted above, and they are but 

 representative of many other similar views receiving the general 

 support of epidemiologists, it will be evident that at the present time 

 the cause of epidemic diarrhoea is to be found in four conditions, 

 which may be expressed shortly as two propositions, thus: (1) 

 Epidemic diarrhoea is a bacterial disease ; (2) its occurrence depends, 

 wholly or partly, upon surrounding temperature, deficiency of rain- 

 fall, and pollution of food, chiefly milk. The exact relationship 

 which these conditions have to each other is not known. Some 

 authorities hold that a certain temperature affects food, conducing 

 towards creating in it injurious properties. Others believe that it 

 is a question of pollution of milk by dust, which carries to the milk 

 the causal micro-organisms, and that deficient rainfall favours this 

 contamination, and increased temperature favours the growth and 

 multiplication of the bacteria thus conveyed to the milk. As Dr 

 ISTewsholme says, "Whatever be its mode of operation, a frequent 

 fall of rain during the summer weeks, even though its total amount 

 be not great, is one of the most effectual means of keeping down 

 the diarrhoeal death-rate "; f and whilst he considers temperature 

 conditions of great importance, "rainfall is more important than 

 temperature in relation to epidemic diarrhoea." Eain washes the air, 

 if the expression may be allowed, and carries to the surface aerial 

 dust. It, of course, also washes the surface of the soil and removes 

 surface pollution, and with it micro-organisms capable of infecting 

 infants, usually by food. Thus the relationship between these 



* Puhlio Health, 1S99-1900, vol. xii., pp. 139-213. 

 I Annual Report on Health of Brighton, 1902, p. 48 



