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THE TRANSMISSION OF PATHOGENIC MICRO-ORGANISMS 

 BY FLIES IN SAINT LUCIA. 



By Lucius Nicholls, B.A., M.B., B.C. (Cantab.). 



The mechanical conveyance of germs by flies and other insects is of importance 

 not only to the sanitary officer, but to the agriculturist and even to the merchant, 

 for the more the matter is enquired into, the more numerous become the cases in 

 which the origin of fermentation or disease in plants and animals can be traced 

 primarily to this agency. Whatever may be the significance of this question in 

 temperate climates, it is obviously of far greater importance in the tropics, where 

 insects are present in greater profusion throughout all seasons of the year. The 

 subject certainly merits more attention than has yet been bestowed upon it. 



Flies undoubtedly plays an important role in those countries in which dysentery, 

 typhoid, cholera, yaws, ulcers, intestinal worms, &c, are common ; and when we 

 consider how often tubercle bacilli are found in the faeces of tuberculous patients, 

 it is quite possible that even such a disease as this may at times be conveyed 

 to the uninfected by the agency of these insects. 



The insects which come in contact with, and find nutriment in, human excre- 

 ment, obviously demand considerable notice from those engaged in the study of 

 sanitation. The degree of importance of each species in this respect varies within 

 wide ranges and is dependent upon a number of factors. The flies undoubtedly 

 head the list, for although there are a number of other insects, such as ants, 

 Psocidae and Coleoptera, which are also found in these surroundings, they are 

 not usually so likely to be a danger to man by coming in contact with his food 

 and water supply. 



In tropical countries where the lower classes are often unacquainted with the use 

 of latrines, swarms of flies are bred in the faecal deposits ; some of these will be 

 found upon food, and in dry weather numbers will be found flying around pools 

 and water supplies, and can be observed alighting at the edge of the water to 

 drink. Some of these species for filthy associations far surpass the common house- 

 fly {Musca domestica), which rarely, if ever, is found breeding in human stools, and 

 which does not naturally seek this matter when there is an abundance of other 

 food. Some species have become adapted to breeding in this situation and are 

 not found elsewhere. 



Musca domestica is not well adapted for experiments to discover the exact 

 relationship of micro-organisms to flies, on account of difficulties in breeding it. 

 Many other species are far more favourable for this work. I have now carried 

 out in Saint Lucia numerous experiments with flies and pathogenic organisms 

 in the attempt to ascertain how long flies are likely to be infectious and whether 

 the infection is present through more than one stage of their life-history. The 

 germs used were the typhoid bacillus and several others of those that do not 

 ferment lactose, besides such organisms as Bacillus prodigiosus and Staphylococcus 

 pyogenes var. aureus. 



The experiments were conducted by exposing human stools in various places 

 on different days for about ten hours, after which time it would be found that 

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