SUMMER DIARRHCEA 15I 



'■ The essential problem in summer diarrhoea is the summer 

 wave, ascending as it does steeply, and descending with but 

 a little less abruptness. It is to this period that the fatality is 

 due. Broadly speaking it corresponds to a similar upward 

 movement and descent of the temperatures registered at a depth 

 of 4 ft. in the soil. The readings of the air thermometer do not 

 correspond closely to the course of the wave of deaths, being 

 subject to considerable fluctuations." 



It has been conjectured that under favourable conditions 

 micro-organisms in the earth multiply and cause diarrhcea. 

 After a full consideration of this subject Niven concludes that 

 " one is driven to abandon the idea that the growth of bacteria, 

 whether in or on the soil, has to do with the annual wave of 

 diarrhoea." 



Another hypothesis is that fruit may be responsible. "But, 

 in the case of diarrhoea, the disease appears first in the infant 

 in house after house, and it is certain that the infant has no fruit ; 

 the effect produced by fruit in the annual course of the disease 

 can therefore only be partial." 



" Another view is that heat may itself cause the disease, or 

 if not the disease at any rate the fatality.... Clearly, however, 

 heat can in no way account for the rapid spread of the disease 

 among particular classes of the population" (see also p. 158). 



Transmission by dust is also an inadequate explanation. 



" What we require for the explanation of the facts of summer 

 diarrhoea is the presence of some transmitting agent rising and 

 falling with the rise and fall of diarrhoea, the features pertaining 

 to which must correspond to and explain the features of the 

 annual wave of diarrhoea." 



" None of the other factors of which we have cognizance do 

 afford such an explanation, and we come by exclusion to 

 consider the house-fly. The process of conveyance of infection 

 is not striking and arresting as it is in military camps abroad ; 

 nor does the number of flies usually approach that observed in 

 tropical and subtropical countries. We are therefore obliged to 

 attack the question de novo, and examine such evidence as we 

 possess to see whether we may rest reasonably confident that in 

 flies we have found the transmitting;' a^ent sought for. 



