340 MEDICAL ENTOMOLOGY 



of bacteria were studied, with the following results : Two were strep- 

 tococci, a few staphlycocci and carcinae and two strains were of B. pyo- 

 cyaneus. Forty-one colonies of the colon group were studied, and were 

 found to contain B. acidi lactici type, B. coli communis type, B. nea- 

 politanus type, B. lactis aerogenes type ; one of the Salmonella group ; 

 one of Morgan's No. I infantile diarrhrea group ; and several of the pro- 

 teolitic group. 



2. The number of bacteria coming from flies, which fall into and 

 struggle in liquids, may be enormous, varying from 2,000 in five minutes 

 to 350,000 in thirty minutes. 



3. Flies caught in insanitary localities contain many more bacteria 

 than those captured in sanitary suburban areas. 



4. Flies caught in milk shops contain many more bacteria than those 

 from other shops where food is exposed for sale. 



5. Flies from the suburban areas have far less bacteria of the infant- 

 ile diarrhoea group than those in the city where the disease is much 

 more common. 



Ledingham and Bacot found that pupae and imagines of Mttsca dome- 

 stica, which were bred out of larvae infected with Bacillus pyocyanens 

 remained infected, although there was no chance of reinfection in the 

 pupal or mature insect stage. In the case of the imago, the infection is 

 at its maximum when it emerges, and it then slowly diminishes. Bacot 

 considers that the ingestion of pathogenic germs by larvae, and their 

 persistence through the pupal stage, as well as in the mature insect 

 which hatches out, are worthy of serious consideration. 



Later Ledingham infected the larvae of Musca domestica with B. typh- 

 osus, but he was unable to recover the bacilli either from the mature 

 larvae, the pupae, or the flies as they hatched out. From the larvae he 

 obtained other bacteria which had contaminated the eggs, and some of 

 these were also found in the flies. When the ova were sterilized with 

 lysol and the larvae which emerged then fed on B. typhosus, he was able 

 to recover the bacilli from the mature larvae and from a single pupa. 



In the same way Graham-Smith showed that, if the larvae of CaUiphora 

 erythrocephala were infected with B. anthracis, the bacilli could be re- 

 covered from quite a large proportion of the flies as they hatched out. He 

 failed, however, to recover B. typhosus, B. enteritidis, B. prodigiosus, and 

 the cholera vibrio from larvae infected in the same way. Nicholls has 

 carried out similar experiments with the larvae of Sarchophagula (a species 

 of Tachinid) infecting them with B. typhosus, B. prodigiosus and Sty- 

 phylococcus aureus, and a lactose fermenting organism ; he found that the 



