154 
Arthropods as Simple Carriers of Disease 
may pas's through their bodies and be scattered in a viable condition 
in the feces of the fly for at least two days after feeding. Similar, 
results have been reached in experiments with cholera, tuberculosis 
and yaws, the last-mentioned being a spirochaete disease. Darling 
(1913) has shown that murrina, a trypanosome disease of horses 
and mules in the Canal zone is transmitted by house-flies which feed 
upon excoriated patches of diseased animals and then pass to cuts 
and galls of healthy animals. 
Since it is clear that flies are abundantly able to disseminate 
viable pathogenic bacteria, it is important to consider whether they 
have access to such organisms in nature. A consideration of the 
method of spread of typhoid will serve to illustrate the way in which 
flies may play an important r 61 e. 
Typhoid fever is a specific disease caused by Bacillus typhosus , 
and by it alone. The causative organism is to be found in the excre¬ 
ment and urine of patients suffering from the disease. More than 
that, it is often present in the dejecta for days, weeks, or even months 
and years, after the individual has recovered from the disease. 
Individuals so infested are known as “typhoid carriers” and they, 
together with those suffering from mild cases, or “walking typhoid,” 
are a constant menace to the health of the community in which they 
are found. 
Human excrement is greedily visited by flies, both for feeding and 
for ovipositing. The discharges of typhoid patients, or of chronic 
“carriers,” when passed in the open, in box privies, or camp latrines, 
or the like, serve to contaminate myriads of the insects which may 
then spread the germ to human food and drink. Other intestinal 
diseases may be similarly spread. There is abundant epidsemiologi- 
cal evidence that infantile diarrhoea, dysentery, and cholera may be 
so spread. 
Stiles and Keister (1913) have shown that spores of Lamblia 
intestinalis, a flagellate protozoan living in the human intestine, 
may be carried by house-flies. Though this species is not normally 
pathogenic, one or more species of Entamoeba are the cause of a type 
of a highly fatal tropical dysentery. Concerning it, and another 
protozoan parasite of man, they say, “If flies can carry Lamblia 
spores measuring 10 to 7 [jl, and bacteria that arc much smaller, and 
particles of lime that arc much larger, there is no ground to assume 
that flies may not carry Entamoeba and Trichomonas spores. 
