498 Mr. A. Bacot on the Persistence of Bacilli in the 
conclusively that certain species of Bacilli ingested during 
the larval period of IZ. domestica can retain their existence 
whilst their host is undergoing the process of meta- 
morphosis and continue their existence in the gut of 
the adult fly after emergence. 
M. domestica, therefore, from its first emergence from 
its puparia, may be an agent in the spread of infecting 
organisms. It is probable that JZ. domestica is not an 
isolated species in this respect. The process of histolysis 
as described by Lowndes in regard to the Blow-fly suggests 
that there is no necessary bar to the continued existence 
of bacilli in the insect’s gut from the larval to adult stages, 
and I have already some evidence that this may prove to 
be the case with insects of another order. The full details 
of the experiments are being published in the Jowrnal of 
Hygiene. 
There remains, however, a point, possibly of more interest 
to entomological than to medical science, as to the source 
of the infection of certain of the control tubes, after the 
inwardly infected but presumably outwardly sterile puparia 
had been allowed to soak for lengthy periods. From five 
to twenty-five minutes was not sufficient to cause infection, 
but periods of several hours or the passage through 
several different media seemed certain to produce infection. 
My own view is that this may be due to the slow passage of 
fluid through the stigmata of the puparia owing to an 
inward suction. It is noticeable that the growth arising 
from soakage as contrasted with pierced or cracked 
puparia is slow and feeble. Where puparia were passed 
through the Bunsen flame the growth in control was in 
comparison strong and rapid; this may have been due to a 
quicker and stronger suction through the stigmata owing 
to the cooling of the heated puparia in liquid or possibly 
to rupturing due to heat. There is another possible way 
by which infection might come about. When the larva 
shrinks into a blunt-ended oval at the close of its active 
existence, the mouth parts are retracted into a small pocket 
on the outward surface of the case ; it seems possible that 
the sterilising fluids do not penetrate freely into this 
intricate passage, with the result that some organisms 
survive, and come in contact with the broth of the control 
tube if allowed to soak for any length of time. In order 
to prevent any possibility of infection by way of the 
stigmata, a further series of experiments were carried out 
