NO. I0 COCKROACHES—ROTH AND WILLIS 23 
may play an important role in the transmission of leprosy. Yet, in 
their conclusions, they ignore their successful experiments in con- 
taminating cockroaches with leprous material which presumably was 
recovered as acid-fast bacilli for a period of two weeks following 
ingestion. 
The possible transmission of leprosy bacilli by insects has not yet 
been exhaustively investigated, but until the epidemiology of leprosy 
is determined, cockroach control should certainly be encouraged in 
areas where leprosy is endemic. 
Herms and Nelson (1913) found more Micrococcus pyogenes var. 
albus on the single pair of hind legs of the German cockroach than 
on the remaining two pairs of legs combined. They attempted to 
explain this heavy infestation as a result of the manner in which the 
cockroach uses its legs in walking; they stated, ‘The tibia and tarsi 
are in contact with the surface on which the insect walks, being 
parallel with the body. Very often the insect stands on the hind pair 
of legs, with the remaining legs barely touching the surface.’ Actu- 
ally, during the normal walking process, the tibiae of the cockroach 
rarely touch the substrate and contact with the surface is made with 
the euplantulae, arolia, or claws, depending on whether the sub- 
stratum is smooth or rough (Roth and Willis, 1952). Perhaps the 
difference in the size of the legs may be a factor in the greater number 
of micro-organisms found on the hind legs; the hind legs being larger 
than the others could harbor more bacteria. Jettmar (1935) found 
that, after Blatta orientalis had walked on a culture of hemolytic 
streptococcus, the cockroach transferred more of the pathogens me- 
chanically from the hind end of its body than from its feet. This 
observation may be related to those of Herms. The cockroach cleans 
its abdomen with its hind legs, using them like a scraper or brush 
(Turner, 1913; Wille, 1920), and in this way could pick up more 
bacteria on its hind legs than on the others. 
Cockroaches are naturally immune to many of the bacteria that are 
pathogenic to man. Most of the micro-organisms listed in Appendix 
B have no effect on the insects. In some instances, the numbers of 
micro-organisms decreased in the cockroaches and could not be re- 
covered from the feces. McBurney and Davis (1930) concluded that 
Salmonella typhosa is either killed in the intestines of Blatta orientalis 
by some unknown agent, or its ability to ferment and to agglutinate 
is destroyed. On the other hand, Morischita and Tsuchimochi (1926) 
tested the sterilizing power of the intestinal contents of Periplaneta 
americana, as represented by a solution of feces. S. typhosa did not 
die even after 3 hours in this solution. Possibly this was too short an 
