A. W. Bacot 
73 
iVIoreover if it is true, as Sharpe supposes, that Miisca domestica hiber¬ 
nates as a pupa, the bacteria must find an asylum in the pupal fly 
during those periods when these diseases in man are in abeyance. 
I may add that I am engaged in similar experiments with fleas, the 
results of which I hope to publish in due course. 
Conclusions. 
1. Pupae and imagines of Musca domestica bred from larvae 
infected with P. pyocyaneus under conditions which exclude the chance 
of re-infection in the pupal or imaginal period undoubtedly remain 
infected with the bacillus. 
2. In the imago the infection is maximal at emergence and then 
diminishes suddenly. 
3. The possibility of a dangerously pathogenic micro-organism 
being taken up by the larva and subsequently distributed by the fly 
is one which deserves serious consideration. 
ADDENDUM. 
By J. C. G. LEDINGHAM. 
{Lister Institute of Preventive Medicine, London.) 
As Mr Bacot points out, the great difficulty in these experiments 
is the efficient disinfection of the pupal exterior before testing the 
bacterial content of the interior. There is a strong probability that 
some of the growth-effects immediately after disinfection are due not to 
organisms still present on the outside of the pupae but to organisms 
from the interior which have gained access to the broth during the 
shaking-up process following disinfection. 
Of those experiments in which disinfection of the pupae was carried 
out by means of 5 lysol acting for ten minutes, two were unsatisfactory 
as the broth tubes in which the disinfected pupae had been washed 
showed growth. From the luxuriant cultures obtained on the agar 
slopes inoculated with the mashed-up pupae, however, there could be 
no doubt that the interior of the pupae was always heavily infected. 
In the last experiment performed with pupae sent me by Mr Bacot 
another method of disinfection was employed. After washing the 
pupae in successive tubes of broth and saline solution, they were 
transferred to a Petri dish containing a small quantity of absolute 
alcohol, where they remained ^or three to four minutes. The alcohol was 
then ignited and allowed to burn out almost completely. Some of the 
pupae, as the result of the process, seemed to be slightly desiccated 
5—5 
