A. W. Bacot 
69 
a positive result. A second series was carried out with faeces contain¬ 
ing B. paratyphosus A which also gave positive results.” 
Although these results are perfectly consistent with the safe passage 
of bacilli (ingested by the larvae) through the metamorphosis they do 
not establish the hypothesis, since the experimental conditions were 
STich that the newly-emerged flies might have re-infected themselves by 
feeding on the contaminated material. There is no evidence in the 
paper that the author separated larvae which had fed on infected 
material and examined the pupa or imagines under conditions which 
would exclude the possibility of re-infection. 
The experiments about to be described were directed to the solution 
of the problem and the results seem fairly conclusive. The species of 
fly used was Musca domestica and B. pyocyaneus as the infecting agent, 
the reasons for choosing this bacillus being that it is not highly 
pathogenic, and is easily recognisable. 
About an inch of dry silver sand was placed in a one-pint card 
cream jar. A mixture of cooked food, consisting of baked milk, rice 
pudding, custard, boiled potato, gristle of meat, was chopped up, and, 
together with the contents of several agar tubes of pure cultures, of 
B. pyocyaneus, was placed on the sand, ova of Musca domestica being 
added. By the time the larvae were from half to two-thirds grown, the 
food was exhausted, so a small quantity of lean uncooked beef was 
minced, wetted with distilled water, mixed with the contents of a tube 
of pure B. pyocyaneus and allowed to remain at 29° C. for three or four 
hours. It was then given to the larvae. When the larvae were full-fed 
all remnants of food were removed and some clean sand added at 
the bottom of jar. 
{a) Experiments on Pupae^. 
1. Five pupae were placed in a 5% solution of lysol for five minutes and then 
washed in sterilized distilled water. Three of these were shaken up in a tube of 
sterile broth for one minute, then removed to a fresh tube of broth in which they 
were torn up with sterilized needles. The tubes were incubated at 29’ C. 
The first remained sterile, the second became turbid in 11 hours, producing an 
apparently pure culture of B. pyocyaneus. 
* Strictly speaking, the case in which the adults of the Muscidae develop is not a pupal 
ease but a puparium. It really consists of the larval skin which is not, as usual, moulted 
but shrinks and becomes hardened by a secretion. The pupal skin itself is of very 
delicate texture. The connection between the pupa and the outer air is by way of two 
semicircular openings at one end of the puparium, these openings are converted into 
efficient filters by an elaborate series of projecting papillae and filaments that would 
effectively prevent the ingress or egress of fluid for some time or until some suction of 
air or expulsion of gas took place. 
