36 THE POPULAR SCIENCE MONTHLY 



THE ROLE OF THE HOUSE FLY AND CERTAIN OTHER 

 INSECTS IN THE SPREAD OF HUMAN DISEASES 1 



By W. E. BRITTON, Ph.D. 



STATE ENTOMOLOGIST, NEW HAVEN, CONN. 



THE rapid progress during recent years in the knowledge and treat- 

 ment of human diseases has been marked by a number of dis- 

 coveries so important and fundamental in their nature that intelligent 

 people everywhere are paying homage to the discoverers, some of whom 

 have given the best part of their lives for the benefit of others. In no 

 line of scientific activity are the results of recent discovery more far- 

 reaching or have they a more important bearing on the daily lives of 

 men, women and children than in medical entomology — or the rela- 

 tion of insects to the transmission of human diseases. 



The diseases that may be spread by insects are of course those that 

 are commonly known as germ diseases, some of which are regarded as 

 contagious or infectious. They are in some cases blood diseases, and 

 affect the entire system, while in others perhaps only one part of the 

 body, or certain organs, are involved. Some, like typhoid fever and 

 tuberculosis, are caused by bacteria, the lowest forms of plant life, and 

 others, like scarlet fever and malaria, by protozoa, which are animals 

 low in the scale of classification. It is manifestly impossible in this 

 paper to place before you all of the evidence, or even brief descriptions 

 of the various studies and experiments which enabled the investigators 

 finally to obtain the facts that make up our present knowledge of the 

 subject. I shall therefore mention only a few of the strategic points 

 and striking illustrations, hoping that these may be sufficient to show 

 the importance of the subject and the necessity for action, and to enlist 

 your interest in it. 



The agency of insects in the spread of human diseases is of two 

 sorts — (1) mechanical carriers, (2) essential hosts. 



To the first group belongs the common house fly, and whatever 

 germs adhere to the body, feet, tongue or wings of the fly in its peram- 

 bulations in and over filth, or those that are swallowed by it, may be 

 deposited on food or in other places in such manner as to cause infec- 

 tion. 



The mosquito is a good example of the second group. One species, 

 Anopheles maculipennis, is one of the necessary hosts in the develop- 

 ment of the malarial parasite. Man is the other host, and in the blood 



1 This paper in substance was given, with lantern slides, before the Con- 

 sumers ' League, New Haven, Conn., May 4, 1911. A few paragraphs are 

 taken verbatim from previous papers by the author. 



