32 THE HOUSE FLY 



a short while his temperature will rise and he will be in the 

 throes of a struggle for life. It is generally supposed that 

 infection and the onset of symptoms of disease follow each 

 other after a very short interval, but this is not so. The 

 microbes need time to multiply and produce the poisons 

 which give rise to the symptoms by which we diagnose the 

 nature of the disease. In the case of typhoid fever, for 

 days before the onset of the characteristic symptoms of 

 the disease, the victim is a source of infection to others, 

 chiefly through the agency of House Flies. 



Although milk and water are at times sources of typhoid 

 infection, the House Fly constitutes the greatest source of 

 such infection. It has been shown that a fly which has. 

 recently fed upon matter infected with typhoid germs not 

 only carries the infection on its feet and body, but that its 

 excrement is a seething mass of typhoid germs. When it 

 is realised that a fly deposits its excrement on every kind 

 of food substance in shops and dwellings, it can easily be 

 understood how flies spread the infection of this dreaded 

 disease. 



Typhoid fever is described by Dr. Sedgwick as " a disease 

 of defective civilisation." Typhoid fever can be practi- 

 cally eliminated from a community by thorough up-to-date 

 sanitation and the destruction of flies. The cause of the 

 disease is a microbe (Bacillus typhosus), and the sources of 

 infection are the stools and urine of those sick with the 

 disease. It can thus easily be realised what a terrible 

 danger the House Fly is as an agent in the spread of this 

 disease. If the excrement of those suffering from typhoid 

 or those convalescent of the disease is accessible to flies, 

 they will most certainly, spread the infection throughout 



