POSSIBLE CAUSAL ORGANLSMS 261 



increasing, the diarrhoea curve begins to fall. The (Ussemination 

 of summer diarrhoea is brought about chieHy owing to the activity 

 of the Hies outside the houses as well as inside. A fall in tem- 

 perature or a spell of dull weather decreases considerably this 

 outside activity and will, therefore, cause a decline in the number 

 of diarrhoea cases. The number of cases of diarrhoea is dependent 

 on the activity of the flies and this is dependent on climatic 

 conditions, chief of which is temperature. Considered in the 

 light of these facts this seeming difficulty is not an argument 

 against the idea that we hold on the relation of flies to summer 

 diarrhoea, but rather one in support of it. 



The relation of temperature and the activity of the flies has 

 also been commented upon by Nash (1909). 



The great difficulty with which we are faced in discussing the 

 question of the .relation of flies to the prevalence of summer 

 diarrhoea is that it has not been proved to the satisfaction of 

 most investigators w^hat the specific pathogenic organism is; or 

 perhaps there are associated organisms. It is possible that more 

 than one etiological factor exists. Various organisms have been 

 found in the diarrhoeal stools. Some epidemics in the United 

 States have been associated w4th the dysentery (Flexner's) bacillus 

 in the stools ; in other epidemics dysentery bacilli w^ere not found. 

 Metchnikoff (1909) believes that Bacillus vulgare may be the 

 causative organism. Morgan (1906-7) isolated a bacillus which 

 he designated " No. 1," and which may be an important factor in 

 the causation of the disease. In a further paper Morgan and 

 Ledingham (1909) give a more complete account of their researches 

 on Morgan's bacillus which belongs to the non-lactose fermenting 

 gi'oup, to Avhich gi'oup all the pathogenic bacteria inducing affec- 

 tions of the intestinal tract belong, namely, the typhoid and 

 paratyphoid bacilli, the dysentery and food-poisoning organisms. 

 In 1905, 58 cases of infantile diarrhoea were examined and 

 Morgan's bacillus was found in 48-2 per cent. ; in 1906, in 54 

 cases it was found in 55 "8 per cent. ; in 1907, 191 cases were 

 examined and it occurred in 16"2 per cent., and in 1908 it occurred 

 in 53 per cent, of the cases, numbering 166 that were examined. 

 It was found that rats and monkeys were susceptible to infection 

 by feeding and that they succumbed after a period of diarrhoea. 



