E. E. Atkin and A, Bacot 
497 
more frequently a total mortality. The infection of a tube with bac¬ 
teria is generally followed by larval progress, usually rapid. The only 
exceptions are cases in which the larvae had existed under sterile con¬ 
ditions for long periods and seemed incapable of adjusting themselves 
to the change. Exceptions to the general rules of rapid larval develop¬ 
ment in infected tubes are most, noticeable in Experiments XII and 
XIII when the bacteria which caused the breakdown in sterility proved 
to be feebly growing species, which altogether failed to keep pace with 
the larval requirements. In Experiments XI, XVI and XVII adults 
were reared under sterile conditions, the greatest success (in Experi¬ 
ments XI and XVI) being attained in a medium of pure beef broth 
(without the addition of salt or peptone) which for some unexplained 
reason seemed favourable for slow but sustained growth. Two adults 
were reared in separate tubes of a 3 % solution of an autolyzed extract 
of brewers’ yeast in distilled water (Experiment XVII). One of these 
was reared under sterile conditions and the other ought, properly speak¬ 
ing, to be credited to these conditions as, although a mould was present 
in the tube when the adult emerged, all the evidence is against any 
suggestion that the larvae obtained any nutriment from this source 
—the presence of moulds being seemingly inimical or neutral to larval 
development; in this particular instance all the remaining larvae in the 
tube died. 
While in these, and in fact in all, cases of larval progress under 
what are apparently sterile conditions, the possibility must not be 
excluded of a slight infection occurring during a portion of the larval 
existence and then dying out, the only evidence in support of such a 
supposition is the fact that larval progress varied in what were appar¬ 
ently sterile tubes independently of the media. This has happened 
in one or more out of a batch of tubes of the same medium, the eggs 
being part of a number all sterilized together. Taking into con¬ 
sideration the variability exhibited by the eggs at a stage when they 
contain fully developed larvae, it will require a considerable body of 
positive evidence based on carefully planned ex;periments before such 
a possibility can be accepted as a probability. 
In Experiment XI a test was carried out to see if a change from one 
sterile medium to another had any effect in stimulating larval growth. 
Of two larvae withdrawn on the 15th day from a sterile tube of peptone 
broth, one was transferred to a tube of broth made from dead insects 
and the other to a tube of water in which horse dung had been steeped. 
After a pause of some 48 hours some evidence of quickened growth was 
