2 INTRODUCTION 



sceptical of the patient's bona fides, when one reads that she 

 invariably concluded by ' chanting the Litany at full length in a 

 clear and beautiful voice'." (Lelean, 1904.) 



The maggots of flies undoubtedly do useful work in devouring 

 decaying matter of various kinds, but the flies themselves " do 

 not display the sort of intelligence we appreciate, or the kind of 

 beauty we admire, and as a few of the creatures somewhat 

 annoy us, the whole Order is only too frequently included in the 

 category of nuisances that we must submit to. It is therefore 

 no wonder that flies are not popular and that few are willing to 

 study them, or to collect them for observation." Thus wrote 

 Sharp in 1899 (p. 439), but since that time many of the blood- 

 sucking types, concerned in the transmission of protozoal 

 diseases, have been accurately studied, and attention has been 

 directed to some of the non-blood-sucking types. It has been 

 proved that various species of the blood-sucking or biting flies 

 are the necessary secondary hosts of the causative micro- 

 organisms of various diseases affecting both men and animals. 

 These diseases are clue to protozoon (animal) parasites, which 

 usually undergo developmental changes within the bodies of the 

 flies, changes which are necessary for the completion of their 

 life-cycles. Some of the most striking hygienic triumphs, as in 

 making the Panama Canal Zone habitable and even healthy, 

 have been due to the knowledge derived from the study of the 

 habits of biting flies and their relation to disease. 



Since non-biting flies cannot act as agents in spreading 

 such diseases their study, until recently, has been neglected. 



In this book an attempt has been made to place before the 

 reader a summary of the more important experiments and 

 observations which have been made, relating to the distribution 

 of disease by non-biting flies. 



During the latter part of the last century a number of papers 

 were published dealing with this subject ; a few contained 

 accounts of careful observations, and a {q.\v produced evidence of 

 an experimental nature, but the majority only offered surmises. 

 Exact observations on the life-histories of flies, experiments 

 on the ways in which they carry and distribute bacteria and the 

 eggs of parasitic worms, and the collection of statistical data 



