NO. IO COCKROACHES—-ROTH AND WILLIS 45 
tanks, or privies. Several species have been found breeding in refuse 
dumps and have been found migrating from both sewers and dumps 
into nearby buildings. The predilection of cockroaches for human 
food and the contamination of food, dishes, and food preparation sur- 
faces by cockroaches are notorious. Thus the mechanism exists for 
the transference of disease organisms by cockroaches to man and his 
animals. 
Although natural transmission of viruses by cockroaches has not 
yet been proved, four strains of poliomyelitis virus have been found 
occurring naturally in wild-caught cockroaches. In addition, cock- 
roaches can harbor experimentally four strains of poliomyelitis virus, 
Coxsackie, mouse encephalomyelitis, and yellow-fever viruses. 
About 40 species of pathogenic bacteria have been isolated from 
naturally contaminated cockroaches. About 90 isolations of natural 
invasions in cockroaches with these organisms have been made. These 
and the following figures include only the reports by each investigator 
of the first isolation of an organism from each species of cockroach. 
Subsequent isolations of the same organism from the same species of 
cockroach by the same investigator are not included. In over 100 ex- 
perimental inoculations of cockroaches with about 40 species of patho- 
genic bacteria, these organisms were recovered from the insects’ feces, 
intestinal contents, or body surface. About 25 of the pathogenic 
bacteria are Enterobacteriaceae. A number of other bacteria of 
doubtful pathogenicity or of doubtful taxonomic status have also been 
isolated from naturally invaded cockroaches. 
Two species of fungi that are sometimes associated with pathologi- 
cal conditions have been isolated from naturally contaminated cock- 
roaches. One species of pathogenic fungus retained its pathogenicity 
after experimental passage through cockroaches. 
So far, only one species of protozoa that is definitely pathogenic to 
man has been found occurring naturally in cockroaches. It was iso- 
lated three times by different investigators. Three species of patho- 
genic protozoa have been used at least 15 times to inoculate cock- 
roaches experimentally. 
The eggs of 7 species of pathogenic helminths have been found 
naturally in cockroaches 11 times. The eggs of 4 of these species and 
of 5 additional species have been fed experimentally to cockroaches 
19 times. Cockroaches have been found to serve naturally as the 
intermediate hosts of 12 species of helminths in about 43 observations. 
Cockroaches were used successfully as intermediate hosts for 11 of 
these species and also for 11 other species in about 44 experiments. 
There is no question about the ability of cockroaches to carry patho- 
