BY N. A. COBB. 183 



overstate, aiid is easily illustrated by a calculation. Reckoning 

 fifty female worms to the individual, an average which I am cer- 

 tain is exceeded in many localities, we have for a population of 

 250,000, the enormous number of two hundred and fifty thousand 

 million eggs, which if distributed evenly over twenty square 

 miles would furnish four to five hundred eggs to the square Joot. 

 They are, however, not distributed uniformly. They are most 

 abundant in the fasces and on the persons of the infected — i.e., 

 about the anus, under the nails and on the clothing. Thence we 

 may trace them in ever decreasing abundance through wash- and 

 bathing-water, &c,, to a more general distribution, — facts so well- 

 known that I need only state them. 



Whatever moves and comes in contact with the eggs is likely 

 to transport them from place to place. Animals, especially flies,! 

 currents of water, currents of air carrying dust, all become agen- 

 cies in disseminating these minute eggs. 



+ On another occasion I have written concerning flies as follows : — 



" Nor are these latter agencies such remote causes as might at first be 

 supposed. It is well known that birds are great travellers, but at certain 

 seasons thej' are outdone by flies. They are, no doubt, in Sydney to-day 

 hundreds of flies that were born and brought up in Melbourne. This is no 

 rash statement. I know of some that arrived in the Iberia ; and they 

 arrive by every train from points more or less distant. I have had an indi- 

 vidual fly under observation for a hundred miles (Springfield to Boston, 

 Mass.), and often for shorter distances. Some flies shut into the waggon 

 with me one evening in Dresden arrived safely in Berlin at midnight, and I 

 have no doulit flew out when the cushions were dusted next morning. 

 Steamers several days at sea generally lose these unwelcome passengers, 

 but I have seen flies on a vessel in mid-ocean, thousands of miles from her 

 last port. 



" But, aside from being conveyed by artificial agencies, these little beasts 

 are no mean navigators of the air. They can fly as fast as a horse can trot, 

 and that for long distances. I have known them to arrive promptly at a 

 vessel anchored above a mile from any object that would aftbrd an alighting 

 place. I have set loose numbers of marked flies, and shortly afterwards 

 recaptured some of them at my neighbours' houses. 



" Do they carry typhoid germs ? Doubtless. Darwin found 537 seeds to 

 have existed in three teaspoonfuls of ordinary pond-mud taken at random, 

 and suggested that hastily flushed water-birds carrying such mud on their 

 feet must become distributors of such seeds. A fly is just as capable 

 of carrying disease germs as a duck of can-ying Juncus seeds. 



" I can advance no instance in which flies have been known to carry 

 typhoid germs, but that they carry about on their feet much larger objects, 

 namely, the spores of common mould, I have repeatedly observed. The 

 mould-spores are not large oljjects, are in fact invisible. Still a sufficiently 



