﻿84 LUCIUS NICHOLLS — THE TRANSMISSION OF PATHOGENIC 



(e.) Another 12 pupae which were about to hatch out gave the following 

 colonies for two and a half cubic centimetres of the broth : — Five pupae gave 

 between 10 and 40 colonies ; seven pupae gave less than 10 colonies, and of these 

 two gave only two colonies each, and another was sterile. 



There are certain possibilities of error in this experiment, but it is at least 

 sufficient to show definitely that during development the fly possesses very great 

 powers of destroying micro-organisms. The experiment when repeated with 

 another species of fly {Sarcophaga) gave similar results. 



Experiment II. 



A number of faecal masses were mixed up with emulsions of Bacillus typhosus, 

 or an organism of this group which did not ferment lactose and which I had 

 recently isolated from a stool, or Bacillus prodigiosus, or Staphylococcus pyogenes 

 var. aureus. They were now exposed to flies and attempts made to trace the 

 organisms through the resulting larvae and pupae. 



When the organism could be isolated from the breeding material it could be 

 isolated from the larvae if they were used at once, but even in the faecal matter 

 these organisms became progressively less, though I obtained the typhoid organ- 

 ism for 17 days, using the malachite green method. 



If the larvae were removed for a few hours before experimenting with them, 

 the germ could not always be grown. Thus, after four hours the typhoid bacillus 

 was obtained five times in 12 attempts ; Bacillus prodigiosus was obtained twice 

 and the Staphylococcus seven times. In none of the experiments did I succeed 

 in isolating any of these organisms from the interior of a pupa. 



Experiment III. 



(a.) A very large number of pupae were transferred to a sterile glass basin. 

 On the day that the flies were due to hatch out they were carefully examined ; 

 one or two were seen to be about to hatch out ; these were removed, and as the 

 head of the fly appeared it was seized with sterile forceps, pulled out, and placed 

 in peptone broth, and from this plate cultures were prepared. In all, 12 flies 

 were examined ; from 10 one or two colonies grew ; two were sterile. 



(b.) Recently hatched-out flies which had not fed were transferred to a dry 

 sterile vessel for two days, then they were chloroformed, the heads and ends of 

 the abdomen were snipped off, the interior extracted and smeared upon agar- 

 agar. Not in one of 12 cases did a single colony appear. 



This complete sterility of starved newly hatched flies appeared so extra- 

 ordinary considering their recent associations, that another series was used, a 

 different fly {Sarcophaga) employed and killed by smashing the head between 

 forceps, to eliminate the possible action of a killing vapour. Ten out of the 

 12' were sterile to agar-agar, and only a few colonies appeared in the other 

 two cases. 



Thus, with flies hatching out from faecal matter, there are two important 

 points : — 



(1) their moving away from the matter in order to pupate ; (2) their power 

 of destroying micro-organisms during their development. 



