296 THE CARRIAGE OF VARIOUS MICRO-ORGANISMS 



a fly which had been feeding upon the spores of this fungus left 

 tracks of fungal spores on the sides of the glass vessel in which 

 it had been contained. The spores from five of the tracks were 

 calculated and the number of spores per track was estimated to be 

 860,000. The possibility of the spores being carried by flies in 

 this way was indicated by the fact that such spores germinated 

 under suitable conditions. 



Bacteria on flies cajitured tinder natural conditions. 



In addition to the investigation of Giissow, which I have 

 recorded at the beginning of this chapter, a series of carefully 

 conducted experiments has been carried out by Cox, Lewis and 

 Glynn (1912) with a view to ascertaining the number and varieties 

 of bacteria carried by flies infected under natural conditions in 

 sanitary and unsanitary city districts in Liverpool. The flies were 

 captured in sterilised wire traps which were exposed for twenty- 

 four hours. Flies from various districts were allowed to swim in 

 measured quantities of sterile water to simulate the pollution of 

 liquids when flies fall into them and to estimate the rate at which 

 the bacteria are given off. This experiment also served to indicate 

 the comparative number of bacteria set free from the bodies of flies 

 from dirty or more cleanly areas. The same flies were afterwards 

 ground up in a sterile mortar with a sterile pestle to find the 

 gi-oss number of bacteria carried on and in a fly and to ascertain 

 whether the number carried inside a fly is always greater or less 

 than the number set fi-ee even after struggling in a liquid for 

 30 minutes. Over 450 naturally infected flies were caught during 

 September and the early part of October 1911 in different parts 

 of the city of Liverpool and the number and kinds of bacteria 

 carried and contained by them were investigated. Their experi- 

 ments showed that : 



1. The number of bacteria derived from flies while 

 struggling in a liquid may be very large and increase with 

 the time they remain in the liquid. The number of bacteria 

 varies from 2000, the lowest figure for five minutes, to 

 350,000, the highest figure for 30 minutes. This number 

 niay be taken as a measure of their capacity to pollute 

 liquid with their vomit, excreta or bodies. The number of 



