﻿86 LUCIUS NICHOLLS — THE TKANSMISSION OF PATHOGENIC 



actually touching them, and they will immediately return. If undisturbed, they 

 engorge themselves with pus, blood, serum or sebaceous secretion, until their 

 abdomens are greatly distended. 



Fig. 3. — Oscinis pallipes,lAW. x 16. 



The " vegetable fly " (Drosophila melanog aster, Mg.) is always found swarming 

 round fermenting cocoa, and I have obtained, by cultures and saccharine medium, 

 the cocoa yeast (SaccJiaromyces theobromae) 24 hours after the fly had fed. 



It is extremely difficult to carry on these experiments for any length of time 

 as most flies quickly die in captivity, and naturally, feeding introduces an error, 

 as the fly infects its food and thus reinfects itself. 



Limosina punctipennis* lives and breeds almost exclusively upon human excre- 

 ment, and in exposed places swarms of this little fly will be found. The only 

 other situations in which I have caught it have been water-pools, rivers, and 

 ravines in very dry weather, when it will fly a considerable distance in search of 

 water. After a long period of dry weather I placed a small pan of water in a 

 patch of " bush " to which labourers were accustomed to resort, and in which 

 these flies were consequently plentiful. Soon numbers of them were seen alight- 

 ing on the vessel at the edge of the water and drinking ; the next nearest water 

 was about 100 yards away, and here also the flies were seen. The pan of water 

 was left here for several hours ; it was then removed and examined for faecal contam- 

 inations by means of cultures, and Bacillus coli communis was obtained. This 

 experiment was repeated upon two other occasions, and in one of these cases the 



8 [Mr. E. E. Austen has kindly supplied the following note on Limosina punctipennis, Wied.: — 

 " This species occurs throughout the Tropics, from Brazil to Formosa. Originally described 

 from a specimen from the ' East Indies,' it has since been met with in South Formosa and 

 North-West India, Java (on excrement, apparently of a monkey : — J. C. H. de Meijere, Tijdschr. 

 v. Ent., LIY, 1911, p. 425), Hawaii (2,000-4,000 ft.), West Africa, Cuba, St. Vincent, and 

 Brazil. Osten Sacken, who found the fly " abundantly in Cuba," and redescribed it under the 

 name Borborus venaliclus, regarded it as probable that the insect had been carried from Africa 

 to Cuba in slave-ships, — a hypothesis which may be correct, but is naturally incapable of 

 proof."— Ed.] 



